Macros in Nim – Tutorial — Macros in Nim

# nim c -d:release --nimcache:lixo -o:rd.x rd.nim
import os, strutils, sequtils, sugar
proc avg(xs: seq[float]): float =
  result= 0.0
  var n= 0.0
  for x in xs:
    result= result + x
    n= n+1.0
  result= result/n

proc main() =
  if paramCount() < 1: quit("Usage: " & paramStr(0) & " ")
  let s = readFile(paramStr(1)).splitWhitespace.map(x => x.parseFloat)
  echo "Sum= ", s.foldl(a + b), " / Average= ", avg(s)

main()

_processfile
figure:: Read and process a file

Let us find out how many students graduate from
medical schools in California. The grad.data
file gives the number of graduates from each
school. The rd.nim program prints the addition
and the average. Here is how to compile and run
the program of listing :ref:processfile –

src> nim c -o:rd.x -d:release rd.nim  # Compile 
src> cat nums.data                    # Check the data
190   45 23 34 89 96 78
97 14 17 54 345 3 42

src> ./rd.x nums.data                 # Run the program
Sum= 1127.0 / Average= 80.5

The predicate paramCount() < 1 checks whether the file name is
present on the command line. If it is not, the program quits with
a request for the file name. In the snippet below, taken from the
application @readfile, the paramStr(0) string contains the
application name.

  if paramCount() < 1:
    quit("Usage: " & paramStr(0) & " ")

The local variable s receives the result of a sequence of
operations on the file contents. The readFile(paramStr(1))
operation reads the file whose name is on the command line.
The nums.data file contains space separated numbers that
.splitWhitespace parses and produces a sequence of strings.
Finally, map(x => x.parseFloat) transforms this sequence
into floating point numbers that foldl(a+b) adds up.
The avg(xs: seq[float]) sums the floating point numbers
into the result variable and calculates the length of
the sequence into n. The average is result/n.

{width=250px}

The first computer was constructed by Konrad Zuse,
a German civil engineer, and his assistant,
Ms. Ursula Walk, née Hebekeuser. Ancient computers,
like those of Zuse and Walk, were based on relays.
These are bulky electrical devices, typically incorporating
an electromagnet, which is activated by a current
in one circuit to turn on or off another circuit.
Computers made of such a contrivance were enormous,
slow, and unreliable. Therefore, on September 9th, 1945,
a moth flew into one of the relays of the Harvard Mark II
computer and jammed it. From that time on, bug became
the standard word to indicate an error that prevents
a computer from working as intended.

Due to bugs, compilers of languages like Nim and Haskell
frequently return error messages, instead of generating
code and running the corresponding programs. The Steel
Bank Common Lisp language does not interrupt code
generation when the compiler spots a bug, all the same
it does issue warnings that help find the problem before
the embarassment of failure being manifest on the client’s
terminal.

# nim c -d:release -o:csv.x --nimcache:lixo csv.nim
import os, strutils, sequtils, sugar

proc main() =
  if paramCount() < 1: quit("Usage: " & paramStr(0) & "fname.data")
  let
    s = readFile(paramStr(1)).split(Whitespace+{','})
    xs= s.filter(x => x.len > 0).map(x => x.parseFloat)
  echo "Average= ", xs.foldl(a+b)/float(xs.len)

main()

#[ 
   Compile:  nim c -d:release -o:csv.x --nimcache:lixo csv.nim
   src> cat csv.data
   190, 180, 170, 160, 120,  100
   100,90  

   src> ./csv.x csv.data
   Average= 138.75
]#

The program above calculate the average of comma separated values.
Everything that comes between #[ and ]# is comments. Therefore,
the comments are giving an example of how to compile and use the
program. Text that comes after # and the end of line is a comment
as well. This second kind of comment is used is very common in shell
commands.

The split(Whitespace+{','}) operation splits a string with
values that can be separated by any combination of chars that
belong to the Whitespace+{','} set. Since split produces
empty "" strings, the program applies filter(x => x.len > 0)
to the result, in order to eliminate zero-length strings from
the sequence.

# nim c -d:release -o:ird.x --nimcache:lixo ird.nim
import os, strutils

iterator valid[T](a: seq[T]): T=
  for x in a:
     if x.len != 0: yield x

proc avg(xs: seq[string]): float =
  result= 0.0
  var n= 0.0
  for x in valid(xs):
    n= n+1
    result= result+x.parseFloat
  result= result/n

proc main() =
  if paramCount() < 1: quit("Usage: " & paramStr(0) & " fname")
  let
    s = readFile(paramStr(1)).split(Whitespace+{','})
  echo avg(s)

main()

#[
src> nim c -o:ird.x -d:release --nimcache:./lixo ird.nim
src> ./ird.x csv.data
138.75
]#

# nim c -d:release -o:xrd.x rd.nim

import os, strutils, sequtils, sugar
proc main() =
  proc avg(xs: seq[string]): float=
     var sm, n = 0.0
     for i, x in xs:
       try:
          sm = sm + x.strip.parseFloat
          n= n + 1.0
       except: discard
       finally: result= sm/n

  if paramCount() < 1: quit("Usage: " & paramStr(0) & " filename")
  let xs = readFile(paramStr(1)).split(Whitespace+{','})
  echo avg(xs)

main()

You will find exceptions in many languages, therefore I
believe that the program above will not pose difficulties.
The avg procedure does not try to eliminate invalid strings
from the sequence. Since the program is not sure that the
string represents a valid floating point number, it tries
to parse it. If the avg procedure fails to parse a string,
the error is captured in an exception section and discarded.
Let us compile and test it:

› nim c -o:excrd.x -d:release --nimcache:del --hints:off excrd.nim

~/nim/tutorial/src
› ./excrd.x csv.data
138.75

I defined the avg procedure inside the main procedure,
just to demonstrate that this is possible. The procedure strip
eliminates blanks around the string, before parsing it to floating
point numbers. This is not strictly necessary, but I did it just to
be on the safe side.

# nim c -d:release -o:rpn.x --nimcache:lixo rpn.nim
import os, strutils
type LL= ref object of RootObj
    car: float
    cdr: LL

template car(a:untyped) : untyped=
  if a == nil: quit("Empty stack")
  else: a.car
template `>>` (a,b:untyped): untyped= LL(car: a, cdr: b)

proc eval(x: string, s: var LL)=
  try: s= x.strip.parseFloat >> s
  except:
    case  x:
      of "+": s= (car s) + (car s.cdr) >> s.cdr.cdr
      of "x": s= (car s) * (car s.cdr) >> s.cdr.cdr
      of "/": s= (car s.cdr) / (car s) >> s.cdr.cdr
      of "-": s= (car s.cdr) - (car s) >> s.cdr.cdr
      of "neg": s= -(car s) >> s.cdr
      else: quit("Error in eval")

var stk: LL = nil
for i in 1 .. paramCount(): eval(paramStr(i), stk)
while stk != nil:
  echo stk.car
  stk= stk.cdr

3×25320+6×56750+2×136000+136000 

src> ./rpn.x 3 25320 x  6 56750 x + 3 136000 x +
824460.0

APP=

ifeq ($(APP),)
abort:
	@echo Usage: make APP=sourceFile
endif

all:
	nim c -o:$(APP).x -d:release --hints:off --nimcache:lixo $(APP).nim

ifeq ($(APP),)
clean:
	@echo Usage: make clean APP=file without extension
else
clean:
	rm -rf $(APP).x lixo
endif

src> make -f Makefile APP=rpn

	nim c -o:$(APP).x -d:release --nimcache:lixo $(APP).nim

CL-USER> (draw-cons-tree::draw-tree (list 2 4 8 16))
[o|o]---[o|o]---[o|o]---[o|/]
 |       |       |       |
 2       4       8       16

# make APP=quoteLoop
import macros, strutils, os

macro magicWord(statments: untyped): untyped =
    ## Designed by Steve Kellock
    result = statments
    for st in statments:
          for node in st:
                if node.kind == nnkStrLit:
                     node.strVal = node.strVal & ", Please."

macro rpt(ix: untyped, cnt: int, statements: untyped)=
  quote do:
    for `ix` in 1..`cnt`:
      `statements`

rpt j, paramStr(1).parseInt :
  magicWord:
     echo j, "- Give me some bear"
     echo "Now"

(@firstmacro) My first macro

Until not long ago, Lisp was the only language that had
macros. Not any more. Nim macros will allow you to design
new commands for the language.

The first thing to understand about macros is that they
don’t belong to the application that you wrote, but are
part of the compiler.

rpt j, paramStr(1).parseInt :
  magicWord:
     echo j, "- Give me some bear"
     echo "Now"

for j in 1..paramStr(1):
  magicWord:
    echo j, "- Give me some bear"
	echo "Now"

for j in 1..paramStr(1):
  magicWord:
    echo j, "- Give me some bear, Please."
	echo "Now, Please."

~/nim/tutorial/src
› make APP=quoteLoop
nim c -o:quoteLoop.x -d:danger --hints:off quoteLoop.nim

~/nim/tutorial/src
› ./quoteLoop.x 2
1- Give me some bear, Please.
Now, Please.
2- Give me some bear, Please.
Now, Please.

# make APP=rep
# Based on a model by Juan Carlos Paco
import macros

macro iter(i:untyped, c1:untyped,
            c2:untyped, stm:untyped): untyped =
  result = newNimNode(nnkStmtList)  # creates an empty result
  var for_loop=
    newNimNode(nnkForStmt) # creates a for-loop
  for_loop.add(i) # adds index `i` to the for-loop

  var rng = # creates a range
    newNimNode(nnkInfix).add(ident("..")).add(c1,c2)
  for_loop.add(rng)  # inserts the range into for_loop
  let spc= newLit("- ") # Creates a space string Lit
  var wrt = newCall(ident("write"),ident("stdout"), i, spc)
  var stmList= newNimNode(nnkStmtList)
  stmList.add(wrt)
  for s in stm: stmList.add(s)
  for_loop.add(stmList)
  result.add(for_loop) # insert for_loop into result

iter(i, 0, 3):
  echo "Hello, world."

› make APP=quoteLoop
nim c -o:quoteLoop.x -d:danger --hints:off --nimcache:lixo quoteLoop.nim
CC: stdlib_io.nim
CC: stdlib_system.nim

~/nim/tutorial/src
› ./quoteLoop.x 3
1- Give me some bear, Please.
2- Give me some bear, Please.
3- Give me some bear, Please.

Now, let us revisit the problem of writing an rpn
calculator. The previous calculator had a serious
problem, it quitted the program between one
calculation and the next, and the values stored
on the stack were consequently lost. This problem
was solved in the version shown in listing @calc.
The calculators of listing @rpn and @calc are
quite similar, and I believe that you will be able
to figure out what is going on in listing @calc
without further explanations.

The novelty in listing @calc is the stdin.readLine(s)
function that tries to read a line into s from stdin
and produces a Boolean true in case of success.
Then, the s var is tokenized and each token x is
presented to eval(x, stk) to be evaluated, as before.

import os, strutils, math

type LL= ref object of RootObj
    car: float
    cdr: LL

template car(a:untyped) : untyped=
  if a == nil: quit("Empty stack")
  else: a.car

template `>>` (a,b:untyped): untyped= LL(car: a, cdr: b)

proc eval(x: string, s: var LL)=
  try: s= x.strip.parseFloat >> s
  except:
    case  x:
      of "+": s= (car s) + (car s.cdr) >> s.cdr.cdr
      of "x": s= (car s) * (car s.cdr) >> s.cdr.cdr
      of "/": s= (car s.cdr) / (car s) >> s.cdr.cdr
      of "-": s= (car s.cdr) - (car s) >> s.cdr.cdr
      of "expt": s= pow(s.cdr.car, s.car)  >> s.cdr.cdr
      of "fv": s= pow(1.0 + s.cdr.car/100, s.car) *
                      s.cdr.cdr.car >> s.cdr.cdr.cdr
      of "neg": s= -(car s) >> s.cdr
      else: quit("Error in eval")

var s=  ""
var stk: LL= nil
var stack: LL= nil

stdout.write "> "
while stdin.readline(s) and s != "quit":
  for x in s.splitWhitespace:
    eval(x, stk)
  stack= stk
  while stack != nil:
    echo stack.car
    stack= stack.cdr
  stdout.write "> "

~/nim/tutorial/src
› make APP=rdwrt
nim c -o:rdwrt.x -d:danger --hints:off --nimcache:lixo rdwrt.nim

~/nim/tutorial/src
› ./rdwrt.x
> 2.5 100 /
0.025
> 1 +
1.025
> 3 expt
1.076890625
> 100_000.00 x
107689.0625

~/nim/tutorial/src
› ./rdwrt.x
> 1.0 0.08 + 2 expt 10000 x
11664.0
> quit

~/nim/tutorial/src
› ./rdwrt.x
> 10_000.00 8 2 fv
11664.0

In order to build a computer that performs medical
diagnosis, launch the Luna 3 to photograph the far
side of the Moon, or even to apply to medical
residency programs in 110 hospitals, you need three
things: Money, training and collaboration. If I had
not obtained the collaboration of Vindaar and Juan
Carlos Paco, I would not be able to write about
Nim macros. If the members of the Della-Vos group
were not trained in such fields as biotechnologies,
microelectronics and medicine, they would not be
able to build bioFETs or measure ion-drifts in the
ionosphere. Later, I will elaborate on training and
collaboration. For the time being, let us learn the
basics of money.

Money is a tool that provides three functions or
services: Medium of exchange, store of value and
unit of account.

To understand medium of exchange, let us perform a
thought experiment. What would the economy in a
Brazilian indian tribe look like, if that tribe
lived without any significant contact with modern
global civilization? Let us give this tribe a
name– Awa, since I lived among the Awaians for
almost three years and could observe their customs,
and became friend of many members of the tribe.

There are people among the Awaians that I will call
croppers, because they work in agriculture: they plant
manioc, corn, rice and beans. There are also breeders
that raise poultry for the eggs. The artisans produce
artifacts like bows, arrows, wicker baskets, hammocks,
etc. A potter provides ceramic ware, and also cups
carved from wood. The healer knows the secrets of
manufacturing medicines and alkaloid arrow poisons.
There are also the hunter-gatherers that obtain foods
and other goods by foraging, i.e., collecting plants
in the forest and pursuing wild animals.

A hunter-gatherer girl, my friend Jurema, uses
a blowdart for capturing small animals and defending
herself. Curare is a common name for various arrow
poisons that causes muscle weakness by competitively
inhibiting one of the acetylcholine receptors. Let us
assume that Jurema needs this concoction for her
blowdarts that she uses for defending herself against
the illegal gold panners that often invade the Awaian
territory in the eastern Amazon rainforest. She goes to
the healer and barters a parrot chick that she captured
in the woods for a small quantity of curare. If the
healer needs a ceramic cauldron for preparing chemicals
and herbs, he may go to the potter’s tent and trade
a quinine based malaria medication in exchange for the
ceramics. A cropper can provide corn to the artisan
and barters it for a hammock that she needs at home.

The aforementioned social organization is what
anthropologists call a barter economy. The idea behind
such an economy is that goods or services are exchanged
directly and immediately, without delay. Of course, long
term barter societies do not exist, and never did,
although they can appear for short periods in countries
plagued with rampant inflation.

To understand why a barter society would face serious
economic crisis, let us suppose that the healer arrives
with the quinine at the potter’s tent, but the potter
already has all the quinine he needs for the time being:

“I am sorry my friend, but I still have the whole lot
of quinine that you provided me the last time we bartered.
Since Madam Tu Youyou discovered artemisin and Chinese
merchants are providing us with the drug, quinine is not
much in demand anymore.”

In this case, he would not provide the cauldron that the
healer needs so badly. It is also possible that Jurema
will not be able to get the curare in exchange for the
parrot chick: The healer may not like parrot chicks, or
his daughter may already have five parrot chicks, and he
does not want to humor her and add a sixth chicken to
her collection.

The problem with a barter economy is that the buyer
pays with a very specific item that the seller may
not need or cannot store at that particular moment.
A small improvement to the barter economy that could
make it viable would be a gift exchange system, where
the buyer pays with a debt of gratitude. In such a social
organization, Jurema goes to the healer and obtains the
needed curare without any immediate exchange of goods.
This therefore means that she now owes a favor to the
healer, which is better known as a debt of gratitude.
How does one pay a debt of gratitude? In this case, in
the future, when the healer needs feathers for ceremonial
dress in a ritual, he can order Jurema to collect feathers
of color and type he needs during her next forage in the
forest. On the other hand, the healer would receive the
cauldron from the potter without immediate payment. When
the potter needs a mosquito repellent from the healer,
all he needs to do in order to obtain it is to remind the
healer of the cauldron received as a gift.

The Awa tribe actually exists as a gift culture. This is
only possible due to the fact that the Awaian population
consists of few individuals. Awaians can remember the
persons to whom they owe favors, and who owes favors to
them. If a society becomes large, it is difficult for a
seller to track the many people who have debts of gratitude
to pay. It is also difficult to decide what could be consider
as equal payment between debts of gratitude. How many times
does the healer need to provide medicine for a cauldron?
Is a repellent for mosquitoes equivalent to a bottle of
quinine? How many feathers are necessary to pay for a
portion of curare?

Therefore, large human populations created tokens to remind
people of their debts of gratitude. For instance, Mayans used
cocoa beans as debt reminders. The advantage of such a system
is that a Mayan did not have to receive the debt only from
the person to whom he provided a service. In such an organization,
a Mayan healer could take the cocoa beans that he received from
the hunter-gatherer girl and use them to pay the potter for
the cauldron.

Cocoa beans as a medium of exchange also have a problem: It is
very easy to cheat the system. For instance, a Mayan crook
could find a cocoa tree, harvest a lot of cocoa beans, and
tell the potter, the healer or the hunter-gather girl that
they owe him that many favors. To avoid this kind of dishonest
behavior, most civilization replaced simple tokens such as
cocoa beans with something harder to falsify, such as coins
of gold, silver and other rare metals.

Of course, falsifications continued even after the introduction
of metal coins. People minted coins of tin, and gold plated them.
Therefore, the gypsies used to bite the gold coins to check that
they had the consistency of gold. Another trick to cheat the
system was to scrape some gold from the edge of a coin. To prevent
this, minters added ridges to the edges. Now you know why coins
have ridged edges.

Coin is the name that experts give to metallic tokens for debts
of gratitude. Gold and silver provides a good method of preventing
people from counterfeiting coins. However, governments decided to
replace gold with a less expensive token. The substitution has the
added advantage of liberating gold reserves for other uses, such
as manufacturing gold nano particles for biomedical diagnostic
assays. In fact, gold is very good for building a device called
lateral flow assay, since it has low toxicity. Besides this,
there exist simple synthesis methods for producing Gold Nano
Particles quickly and inexpensively. If you don’t find a discussion
of the subject in this book, get in touch with the authors and ask
for a chapter on the subject.

For the reasons stated above, gold and silver coins were replaced
by banknotes. In order to defeatforgery, tampering and counterfeiting,
manufacturers of banknotes introduced many technological security
measures, such as special types of paper, micro printing, intaglio
printing, watermarks, guilloché, holograms, security threads,
magnetic ink, etc. One of the most famous security printers, who
helped in the creation of these technologies, was Thomas de la
Rue (1793 – 1866), who founded the De La Rue plc, which today sells
high-security paper and printing technology for over 150 national
currencies.

The function of banknotes, which a citizen holds in his or her
possession, is to remind the society that its members owe a certain
value of services and goods to that particular citizen. It was
introduced when the number of citizens became so large that a person,
like the Awaian girl, could not remember who should pay her a debt
of gratitude. The advent of computers permitted the storing of
commercial transaction records in a data base. The buyer and seller
can access the data base through a smart card personalized to the
buyer. This new technology is known as digital currency.

It is easy to forecast the type of technology that the future
holds for money: The seller and the banking system will not need
the smart card, in order to identify the buyer, since they can
easily be identified through their DNA.

# A syntax changing macro by Vindaar
import macros, strutils, os

proc parseArgs(cmd: NimNode): (NimNode, NimNode) =
  doAssert cmd.len == 2
  expectKind(cmd[1], nnkInfix)
  expectKind(cmd[1][0], nnkIdent)
  expectKind(cmd[1][1], nnkIdent)
  expectKind(cmd[1][2], nnkIdent)
  doAssert cmd[1][0].strVal == "->"
  doAssert cmd[1][1].strVal == "times"
  result = (cmd[0], # cmd[0] must be valid integer
            cmd[1][2]) # identifier to use for loop

macro rpt(cmd: untyped, stmts: untyped): untyped =
  expectKind(cmd, nnkCommand)
  expectKind(stmts, nnkStmtList)
  let (toIdx, iterVar) = parseArgs(cmd)
  result = quote do:
    for `iterVar` in 1..`toIdx`:
      `stmts`
  echo result.repr

rpt paramStr(1).parseInt times -> j:
    echo j, "- Give me some bear"
    echo "Now"

(@sugarmacro) A syntactic sugar macro

In listing @sugarmacro, the untyped stmts behave
exactly as in the other macros used for repetition
that I discussed previously. However, cmd is a NimNode
that bundles the integer expression that determines the
number of repetitions, the keyword times, the infix
arrow -> and the j counting variable. These roles
are determined by the parseArgs procedure that extracts
the important components of this complex syntax, to wit,
the integer toIdx parameter that indicates the number
of repetition and the iterVar that in the example is j.

The parseArgs procedure is amazing, and I would not
be able to design it the way Vindaar did. It starts with
a doAssert cmd.len == 2 that determines that cmd has
length 2. Of course, cmd[0] contains the integer number
of repetitions. As for cmd[1], it contains three components,
the arrow (component cmd[1][0]), the keyword times (component
cmd[1][1]) and the iterVar, which is j in the example.
Of course, the result will be the (cmd[0], cmd[1][2]) tuple.
With the four examples of macros that you and I discussed,
you will be able to become proficient in meta programming
through deliberate practice.

There are two persons that are helping me with this
book, I will call them edu500ac and Marcus. I do not
know much about Marcus, except that he has three
daughters, and that his daugters play the violin.
Mr. edu500ac told me that much about Dr. Marcus,
therefore that much is all I know about him.

Brian Caplan says that, if a girl wants to play the violin
at Carnegie Hall, she needs to practice a lot. I think that
you do not dispute this assertion.

Airline transport pilots must have a minimum 1,500 hours of
flight time. From this training, at least 500 hours should be
cross-country flight time and 100 hours should be night flight.
I don’t know why I am trying to make this point, since everybody
accepts that a pilot must practice a lot before flying a passenger
jet. It is interesting that people who accept that musicians,
physicians and pilots need training do not take this idea to their
own activities.

begin{figure}
begin{tikzpicture}
%aixes knowledge
draw[thick,->] (0,0,0) – (3,0,0) node[anchor= north west]{$y$};
draw[thick,->] (0,0,0) – (0,2,0) node[anchor= north west]{$z$};
draw[thick,->] (0,0,0) – (0,0,5) node[anchor= south east]{$x$};

%dashed
drawdashed – (2.5,0,4);
drawdashed – (2.5,0,4);
drawdashed – (2.5,2,4);
%% drawdashed – (1,1,1);

drawfill=black!100!white circle(.08);
end{tikzpicture}
caption{Position}
label{fig:position}
end{figure}

In this chapter, you will learn that knowledge has 3 dimensions,
the explicit knowledge, the tacit knowledge and the shared
knowledge. You can acquire explicit knowledge from books and
classes, but you need practice in order to gain tacit knowledge.
For instance, you learned the structure of Nim macros, but
without writing a lot of macros you will never become as
proficient as Vindaar.

How to recognize an object? How to distinguish a screwdriver
from a monkey wrench? A set of attributes that characterize
an object is called data. Examples of attributes that could
be used in a classification system: color, position, mass,
volume, density, material, etc. Each attribute can have
different values. For instance, the color attribute can
be black, white, yellow, blue, and
so on. The position on Earth is an attribute that is usually
given by latitude and longitude. Mass can be
measured in kilograms, grams, pounds, etc. Volume may be
given in liters.

begin{figure}
begin{tikzpicture}
%aixes knowledge
draw[thick,->] (0,0,0) – (3,0,0) node[anchor= north west]{$y$};
draw[thick,->] (0,0,0) – (0,2,0) node[anchor= north west]{$z$};
draw[thick,->] (0,0,0) – (0,0,5) node[anchor= south east]{$x$};

%dashed
drawdashed – (2.5,0,4);
drawdashed – (2.5,0,4);
drawdashed – (2.5,2,4);
%% drawdashed – (1,1,1);

drawfill=black!100!white circle(.08);
end{tikzpicture}
caption{Position}
label{fig:position}
end{figure}

According to Descartes, there exists multidimentional
attributes. In modern terminology, one says that the
values of such an attribute are vectors that can be
broken into parts, those partes are called components.
For instance, the position attribute has three dimensions,
which are the x, y and z coordinates. Likewise, one
can see knowledge as having three dimensions, which are
the explicit, tacit and shared components.

Explicit knowledge is anything that one can write in
a book, code into a computer program or teach in a
class room. Tacit knowledge is something that one knows,
but cannot explain how she learned it or use it.
Mexicans know Spanish, but they aren’t able to write
a primer where a resident physician from Miami could
learn to speak fluently to his patients. The difficulty
in teaching Spanish to an adult shows that Michael
Polanyi was right when he stated that we can know
more than we can say.

begin{tikzpicture}
draw[thick,->] (0,0,0) – (2.2,0,0) node[anchor= north west]{$tacit$};
draw[thick,->] (0,0,0) – (0,2,0) node[anchor= north west]{$shared$};
draw[thick,->] (0,0,0) – (0,0,3) node[anchor= south east]{$explicit$};

drawultra thick,-> – (0,0,2);
drawultra thick,-> – (2.5,0,2);
drawultra thick,-> – (2.5, 2,2);
draw[dashed,->](0, 0, 0) – (2.5, 2, 2);
end{tikzpicture}

(@kdimensions) Dimensions of knowledge

In figure @kdimensions, one can see a path to knowledge.
About 1418, Prince Henry the Navigator founded a School
of Navigation in Sagres. In class rooms, a future sailor
was trained in map-making and reading, which is explicit
knowledge that one can write in books. The student would
advance along the explicit axis, as shown in the figure.
Then he would embark in a ship, where he would acquire
actual job skills through hands-on training. Could a
sailor learn about maps while already in a ship? Such
a training method is represented by the dotted path in
figure @kdimensions and is very dangerous. It is like
a physician who would consult the Sobotta to learn
Anatomy while performing a surgery.

One acquire tacit knowledge through training, there is
no other way. Don’t expect to learn how to play the
violin, wrestling, deliver babies or pilot a jet plane
in class room or from books and youtube videos.

The shared knowledge is the one that cannot be found
between our two ears. It is distributed throughout
organizations or guild of experts. For instance,
the knowledge about air combat, on which Manfred von
Richthofen – the Red Baron – excelled, was distributed
between the pilot, who was the Baron himself, and
Anthony Fokker, the Dutch engineer that designed
the Manfred’s triplane. This knowledge was seamed so
well that the Baron could not perceive the stitches.
The Red Baron feel any gaps in his domain of the
airplane, even if the gaps were filled by automatic
contrivances hard wired in the controls by Anthony
Fokker. In fact, any perceptible transition between
engineering expertise and flight tacit knowledge
could hinder the pilot’s ability to anticipate the
consequences of his actions and be fatal in a battle.

I am telling you all this in a tentative of convince
you that this book alone will not take you very
far from the axis of explicit knowledge.

Now, I will give you time for practicing macros.
Meanwhile, I will tell you my story, and how I
got here in Paraguay. Of course, if you are not
interested in my story, you can stop reading here,
and start practicing macros, while your teen ager
daughter train how to play the violin.

# counter.nim
import macros, strutils, os

proc parseArgs(cmd: NimNode): (NimNode, NimNode) =
  doAssert cmd.len == 2
  expectKind(cmd[0], nnkIdent)
  result = (cmd[0], # cmd[0] has an integer expr
            cmd[1]) # identifier to use for loop

macro cnt(cmd: untyped, stmts: untyped): untyped =
  expectKind(cmd, nnkCommand)
  expectKind(stmts, nnkStmtList)
  let (iterVar, toIdx) = parseArgs(cmd)
  result = quote do:
    for `iterVar` in 1..`toIdx`:
      `stmts`
  echo result.repr

cnt j paramStr(1).parseInt:
    echo j, "- Give me some bear"

#[ › make APP=counter
   nim c -o:counter.x -d:danger --hints:off --nimcache:lixo counter.nim
   for j in 1 .. paramStr(1).parseInt:
       echo j, "- Give me some bear"
   › ./counter.x 2
   1- Give me some bear
   2- Give me some bear
]#

(@practice1) A simpler counting macro

When Vindaar provided us with the macro on
listing @sugarmacro, he gave us explicit
knowledge. In fact, since he could present the
macro on paper, it was explicit knowledge. In
order to learn macro designing, it is necessary
practice, and one should start practicing with
simple stuff. In listing @practice1, the definition
of cnt couldn’t be simpler. The cmd parameter
has 2 elements, the first one must be a variable.
The statements below checks whether these two
conditions are met by the cnt macro.

  doAssert cmd.len == 2
  expectKind(cmd[0], nnkIdent)

# infixLoop.nim
import macros, strutils, os

proc parseArgs(cmd: NimNode): (NimNode, NimNode) =
  expectKind(cmd[0], nnkIdent)
  expectKind(cmd[1], nnkIdent)
  doAssert cmd[0].strVal == "++="
  result = (cmd[1], cmd[2]) 

macro rpt(cmd: untyped, stmts: untyped): untyped =
  expectKind(cmd, nnkInfix)
  expectKind(stmts, nnkStmtList)
  let (iterVar, toIdx) = parseArgs(cmd)
  result = quote do:
    for `iterVar` in 1..`toIdx`:
      `stmts`

rpt j ++= paramStr(1).parseInt:
    echo j, "- Give me some bear"

#[
› nim c -o:infixLoop.x -d:danger --hints:off infixLoop.nim

› ./infixLoop.x 3
1- Give me some bear
2- Give me some bear
3- Give me some bear
]#

(@practice2) Macro with an infix operator

Listing @practice2 is my second attempt at building
an interesting macro. This time, cmd has a single
infix expression. I learned that I should not place
an assertion on the length of infix expressions.
For instance, the compiler protests if I add the
following check on the definition of parseArgs in
listing @practice2:

proc parseArgs(cmd: NimNode): (NimNode, NimNode) =
  doAssert cmd.len == 2
  expectKind(cmd[0], nnkIdent)
  expectKind(cmd[1], nnkIdent)
  doAssert cmd[0].strVal == "++="
  result = (cmd[1], cmd[2]) 

It seems that infix expressions do not have length.
I would never discover this if I have not been
practicing in the last three days.

I was born in Provo, a small town in Utah, about 82 miles
from Salt Lake City. If you are not acquainted with
customary units, you will find a good opportunity to
practice Nim in the American units of measurement.
Therefore, let us interrupt my story and deal with
unit conversions. Let us consider only conversions
between miles and kilometers for the time being. You
will discover easily how to deal with other units. Below,
you can see how to use the program of listing @units.

~/nim/tutorial/src
› make APP=units
nim c -o:units.x -d:danger --hints:off --nimcache:lixo units.nim

~/nim/tutorial/src
› ./units.x
> 82 mi km
131.938km
> q

As you are probably aware, there are a lot of Mormons in that
region of the United States. I myself am an atheist, as befits
a physician. The rest of my family are members of The Church of
Jesus Christ of Latter-day Saints, which is the official name of
the Mormon Church. Since The Church of Jesus Christ of Latter-day
Saints is a very long name to write or pronounce, Mormons often
abbreviate it as The LDS Church, an acronym that reminds me
of a popular hallucinogenic drug.

A Mormon believes in many weird doctrines.
According to the doctrine of continuing revelation,
Jesus Christ leads the LDS Church by revealing
his will to its president. The belief is also that
each individual member of the church can receive personal
revelation from God, while getting on
with conducting his or her personal
life. However, I never did, which makes me the only
Mormon to whom God never revealed anything!

Who is this guy that calls himself God?
Apparently, he is a king that rules the Earth from his
throne somewhere near the star Kolob.

# make APP=units
import os, strutils

type
  LL= ref object of RootObj
          h:  U
          t: LL
  UnitKind= enum mi= "mi", km= "km", nm= "nm"
  U = ref object
        case kind: UnitKind
           of mi, km, nm: fVal: float

template car(a:untyped) : untyped=
  if a == nil: quit("Empty stack") else: a.h

template psh(knd: untyped, v: untyped, s: untyped) =
  s = LL(h: U(kind: knd, fVal: v), t: s.t)

proc eval(x: string, s: var LL)=
  try: s= LL(h: U(kind: nm, fVal: x.strip.parseFloat), t: s)
  except:
    case x :
      of "km":
         if (car s).kind == nm: (car s).kind= km
         elif (car s).kind == mi: psh(km, s.h.fVal * 1.609, s)
      of "mi":
        if (car s).kind == nm: (car s).kind= mi
        elif (car s).kind == km: psh(mi, s.h.fVal / 1.609, s)
      else: echo "?"

var s=  ""
var stk: LL= nil
var stack: LL= nil
stdout.write "> "
while stdin.readline(s) and s != "q":
  for x in s.splitWhitespace: eval(x, stk)
  stack= stk
  while stack != nil:
    echo stack.h.fVal, stack.h.kind
    stack= stack.t
  stdout.write "> "

(@units) Unit conversion

I am not entirely sure whether the existence of Kolob
is truly an official doctrine of the LDS Church. In fact,
I never cared to ask for an audience with the Mormon
Church President, in order to learn the whereabouts
of God. But my grandmother was said to have
received a revelation that
firmly placed God’s home in the neighborhood of
Kolob.

A Mormon male who abides by the convenants
that he himself or by proxy made with God
may be considered for priesthood as early as the age of 12.
Let me give you my impressions concerning this particular
doctrine. I think that religion should have
a content rating system similar to the
Motion Picture film rating system.
Buddhism and Jainism could be classified
as entertainment for general audiences.
The Seventh-day Adventist Church do have
some material that may not be suitable
for children. Therefore, a child, who
wants to attend the Seventh-day Adventist
Church, should receive guidance from
a biology teacher or a philosopher.
Teenagers under 17 must be accompanied
by an adult guardian, in order to
attend any other Christian Church.
Finally, no one, 17 and under, should
be admitted in a mosque or synagogue.

There are people, such as the
biologist Richard Dawkins, who think
taking a kid to a Christian temple
is tantamount to child abuse.
Perhaps due to a degree of ignorance
about Dawkins’ books, my grandmother
started to take me to church,
while I was still indeed very young.
I cannot remember how old I was
when I entered a temple for the first time,
but I can assure you that I was
under 17. Notwithstanding, I don’t
want to discuss this child abuse
issue any longer.

Another strange doctrine preached
by the LDS Church is the so
called law of chastity,
which prohibits adultery,
all homosexual behavior, and any
sexual relations outside of marriage.
The impact that this law had on my life
was that I only started a
normal sex life at almost 30
years old; it was then that I discovered
all doctrines of the LDS Church
to be bullshit.

To be fair, I must accept that Mormons are
very tolerant, as the following story will
bear witness. A Study in Scarlet is novel
by Arthur Conan Doyle, where this Scottish
author introduced Sherlock Holmes and Dr. Watson
to the world. Arthur Conan Doyle imitates
the style of the French detective novels
by Émile Gaboriau, who always starts his stories
with an investigation and presents a long flash
back at the second part of the book.

Doyle’s story flashes back to a valley in
Utah, where nowadays is Salt Lake City.
If you read the book, you know that it
paints a bleak portrait of Mormonism that
includes forced marriage and violence.
I was browsing the novel in a large
bookstore in Logan, Utah, when many members
of the LDS church approached and recommended
the book. They have no hard feelings against
the Arthur Conan Doyle, and I am sure that
I will not lose a single Mormon friend for
my bland humor directed against the Church.

There is a custom among members of the LDS Church
that is worth preserving. Young Mormons often go
to distant countries as missionaries. This means
that many couples teach foreign languages to their
kids, when they are quite young, so that they are
apt to spread God’s word to non-English speakers.
For instance, my parents wanted me to serve as a
missionary among South American Indians. To fulfill
my father’s design for me, I started learning
Portuguese and Spanish when I was 3 years old.
Of course, we did not know at the time that Indians,
as a rule, do not speak either Portuguese or Spanish.

To my regret, my father never
saw me taking an airplane from Salt
Lake City airport, in order to teach the
Book of Mormon to Brazilian, Peruvian,
Bolivian or Paraguayan Indians.
Instead of giving this simple joy to
my father, I decided to go to college when
I was 16 years old, and started medical
school when I was 20. After medical school
at the Johns Hopkins School of Medicine,
I spent an additional five years in a
general surgery residency. Therefore, I was
over thirty years old when I finally took
an airplane to Brazil. My father did
not go to the airport to say goodbye.
He passed away three years before
due to a colorectal cancer.

As I said before, my father was
not at the airport for reasons of
force majeure. But my grandmother
was there. She entrusted me with two large
boxes for the Indians, or Lamanites,
as she used to call them. One of the
boxes contained Portuguese translations of The
Book of Mormon. The other box was
heavy with Spanish versions of the
same book. The sacred books were
quite useful in South America,
since my stock of toilet paper
became soaked due to bilge water in
the boat, which I used for traveling
along the Amazon river. On the
other hand, my grandmother’s boxes
were so carefully packaged that
no single book was touched by water.
So the exemplars of the Book of Mormon
provided a good replacement for my
lost toilet paper.

Believe me, I will provide you with
a full account of my years in college,
the medical school at Johns Hopkins,
and my residency training. However,
right now I want to report on an event
that happened while I was living among
members of an Indian tribe in the
north of Brazil. I will not name the
tribe, due to the Hippocratic oath, that
forbids me to divulge in any shape or form
whatever I see or hear in the course of my
profession. In any case, I already named it
when I was writing a chapter on money. The
fact is that, when I writing about women,
money or Italian poetry, I don’t consider
myself a physician, and am not bound to
ancient oaths and convenants.

Upon arriving in Brazil, I heard of a government program
by the name of Mais Medicos, which issues a temporary
medical license, on the condition that the applying
physician takes a job in a remote region of the country.
The pay amounts to 3000 US dollars a month. In this list
of remote regions, there are a few Indian tribal territories.

By the way, the word Indian is the accepted term
that Brazilians use, when they refer to people
descended from the Pre-Columbian indigenous population
of the land. Instead of calling these populations
by some polite noun phrase like Native American,
while depriving them of their lands and properties,
Brazilians reserved 12.5% of the national territory
for Indians. All the same, Brazilians still call them
bluntly – Indians. If a tribe proves that its ancestors
lived in a given region, it can incorporate that region
to their current tribal land. This constitutional
act applies to any tribe, no matter how large the
region is, or how few individuals belong to the tribe.
For instance, Fox/Sun Hills Indigenous Land
is the home to 20000 members of the Macuxi people.
Its perimeter is 629 miles long. In May 2009, the
Brazilian Supreme Court ruled that the Fox/Sun Hills
Indigenous Land should be inhabited only by indigenous
people, and ordered a military operation to remove all
non-indigenous inhabitants. With the addition of Fox/Sun
Hills reservation, 46% of the State of Roraima is set
aside for Indians.

Of course, Brazilian doctors
don’t want their practices in a reservation.
Therefore, Brazilians who live in
large cities like Salvador or Rio
de Janeiro form long lines in
front of large hospitals staffed
by physicians from prestigious
local medical schools, like Unipac
or Unifeso. The Indians must be
content with a doctor graduated
in places like Johns Hopkins
School of Medicine, Harvard Medical
School or Université de Médicine
Paris Descartes.

I must confess that, when I applied
for the job, my goal was not to help
poor Indians who live somewhere in
the north of Brazil. I was envisioning
trips along large rivers
on a jet ski with a pretty French
female doctor riding the pillion.

I must avow that the reality
departed from my daydreams in
many aspects. The girl who often
rode on the pillion was not French,
but an American of Danish descent.
If you know Logan, the home town of
the Utah State University, my Alma
Mater, you know that there are a lot of
people of Danish heritage there.
Family names like Jensen, Mikkelsen and
Jorgensen are commonplace in Logan.
Therefore, I was very disappointed
when I discovered that the closest
European girl from my practice was
in fact not only Danish, but a
Mormon Dane.

I am sure that you will ask:
“Well, what is the difference
if the girl is French or Danish?”
As a French man would say, Il y a
une différence (there is
a qualitative difference).

You certainly noticed that American
or English men go simply crazy over
French, Iranian or Armenian women.
But if a French or Armenian man shows
interest in an American woman, he wants
to marry her to obtain the right to
stay in the United States. Sorry, guys,
what I said is politically incorrect,
but Truth is often politically incorrect.

A research team showed pictures
of pretty women from different
countries to 44000 men in the United States.
The preference rating of American men
was as follows.
Armenian women came first. Bajan
women came in second place in the
preference of American men. Don’t
ask me where Bajan women come from.
I do not have the slightest idea.
French women come third, followed
by Colombian, Brazilian and Bulgarian
women in that order. American and English
women occupied the 9th and 10th
place in men’s preference respectively.
This result would be great for
American women, if the number of
contestants were not 10.

Why do men prefer certain nationalities?
The answer is the ass.
Germanic women often have square butts.
By Germanic women, I mean Anglo-Saxon,
German and Scandinavian women.
A square or H shaped butt is due to the
position of the hip bones, excess fat
around the waist, love handles or genetics.
Armenian, Colombian and French women have
a bigger, rounder and shapely booty.
Before proceeding with my narrative,
I will answer the question that my
American female readers are impatient
to ask. “Doctor, is there a cure for
a square shaped butt?”

Before answering the question, I will
remind the reader, be it female or
male, that Brazilian indigenous people
don’t mind being called Indians, provided
that they receive 12.5% of the national
territory. I hope that American women will
forgive me for being rude to the point
of saying that most of them have square
butts, provided that I tell them how
to get an Armenian butt. And that is the
main point of this book: A sure and
safe way to loose weight and get a
round and shapely ass.

As for my Danish girlfriend, after two years
with me in the Amazon rain forest, and through
following my advice, her butt became so pretty
that you would take her for a Colombian
Wayuu Indian, if she were not blond.
Unfortunately, since she is a Mormon, the only kind
of intimacy that I shared with my Danish
girlfriend were jet ski trips.

Now, I will start my narrative at
the point in time, when I was traveling
on foot to the Indian reservation that
the Mais Medicos program assigned to me.
Pülowi, my guide, was a young Wayuu Indian girl
that entered Brazil illegally across the
Venezuelan border. Due to the economic
crisis in Venezuela, many Wayuu Indians
like Pülowi moved to Brazil, where they pretend to
be native Macuxi.

I did not care to
ask the name of the town
that Pülowi and I were crossing
on that occasion, because a village
in the middle of the jungle like that
one often doesn’t have an official name. It is also
possible that different groups of people
call it by a different name. A policeman that
the authorities have sent to keep law and
order may call it Hellgate! On the
other hand, a drug dealer who takes a break there
while traveling to Colombia or Peru prefers
Stopover. Since I did not learn
its name, I cannot point to that weird settlement on
a map or give you any information about
its location. What I can say
is that the river that flows through the
town flooded, a phenomenon that very
often accompanies the rainy season in that part of Brazil.
As long the rain lasts, a torrent
of water flows along the street
that runs parallel to the river, and
at that time it was no different.

At last the rain ceased. The right hand sidewalk
and the street itself was almost dried out. There
was no car to be seen. I must add that there are
not many cars in the small towns of the Amazonian
rain forest. A boat is more useful in that
region than a car. In that particular town
that Pülowi and I were crossing, one could use
their fingers to count the number of cars.

On the right hand sidewalk, instead of normal buildings
and houses, I noted only white painted walls.
The height of the walls was not uniform, but changed
according to the plot of land that it was marking.
Notwithstanding, every estate seemed to be surrounded
by walls tall enough to hide from view the terrain
and every building that one could imagine on it.

What secrets were being hidden from
inquisitive eyes? Perhaps smuggled goods? Maybe,
that street was a string of chemical laboratories
manufacturing illegal drugs. Another reasonable
hypothesis is that the plots of land were used
to park containers of weapons or stolen goods.
I know that, when you reach the end of this book
without learning the purpose of these high walls
around the tracts of land you will be extremely
frustrated. But, believe it or not, I was too
scared to stay any longer in that unwelcoming place.
What follows will show you that my fear was
not misplaced.
Due to my unwillingness for
any additional exploration,
those walls brought only
one contribution to this logbook:
The inhabitants of the
town that Pülowi and I were traversing are
not good and law abiding people. It would
not take long before my
suspicion was confirmed.

Before proceeding with the narrative,
I will ask the reader to ponder for a moment
about the layout and surprising aspect
of the scenery in the street, through
which I and Pülowi were walking.
A river flows on the left hand side.
On the right, there is a line of walls
without gates or entryways. How can the owners
or their employees reach the
buildings or tracts of land that
the walls surround? In my mind, I was
asking these questions, and to which
I never found a satisfying answer.

Only a far away building broke the
disparate line of uneven walls.
In front of the building, that perhaps
was a movie theater, there was a compact
mass of people.

The building still was far away,
nonetheless I started planning how to make my way
through the mass of people to carry on my journey.

I walked slowly due to the heat that
danced in the still air. One hundred meters
in front of me, Pülowi was running. She
was close enough for me to see with
pleasure the swinging movement of her buttocks.
Whenever she thought that she had distanced
far enough away from me, Pülowi would
reverse the step, run in my direction,
and stop 50 meters in front of me.
There she would practice the monkey jump,
the half moon, and other moves
very popular among Brazilian martial arts
practitioners. After this display, she would
run again forward along the chosen path.

This way, I was walking with regular
steps, while Pülowi kept running forward
and backward, in a zigzag movement. Of course,
she would displace herself in ever longer
distances going forward than coming backward,
so she could advance at the same speed
as her companion, of course that was me.

Since that town seemed to be so
dangerous, people may wonder why
I kept such a slow pace. The northern
part of Brazil is hot as hell, that
is why! During the day, the temperature
often reaches 100 Fahrenheit. What
I think is amazing is not my lumbering,
but the zigzag jogging of the Indian girl.

Although we were advancing very slowly,
due the slow pace that the heat imposed on
me, and Pülowi’s zigzag jogging, we finally
reached the throng of men in front of
the movie theater. The methods that
each one of us chose to cross the horde
could be used by a psychologist to draw
our profile.

The Indian girl penetrated the crowd
boldly, poking people who were at
her right and left sides, kicking anyone
in front of her, squeezing herself forward
like a determined winding snake,
while stepping on any foot that was in her way.
Don’t ask me how she was able to avoid
harassments from the bullies
and attacks from the thugs that
were gathered in their element.
It is possible that the ruffians
thought that she was the lover of
a local drug lord. After all, what
kind of woman could dare to jump
in the middle of such a dangerous
crowd, unless she felt herself
protected by a top dog?

As I told you, there is a river
that flows along the left hand side of
the street. The overflowing water
spread over the left hand sidewalk.
A long flatboat was moored across
the throng. The layout was such that
the crowd took up completely
the narrow space between
the river ship and the movie theater
leaving no room for easy passing.
In fact, the river ship was in itself
long enough in that the bow and
stern were free of this multitude.
I figured that if I entered
the vessel at the bow, walked along
its deck, and disembarked at the stern,
I would get around the crowd.
The point for me was the boat,
in that position, stood out like an invitation
around trouble. I guess that an FBI profiler who
might observe me performing this maneuver,
would deem me a coward, a man prone
at all cost to avoid confrontation.
Pülowi, to the contrary, would be
classified by the same profiler
as a risk taker.

The ship’s taffrail formed the
outermost wall of the cabin.
Judging from the size of the cabin,
one could infer that the boat was
a floating home. However, the owner
was elsewhere in all likelihood.
He could even be mingled in with the crowd in front
of the movie theater, trying to do whatever
the others were doing. The cabin
door opened on deck side,
towards the river.
Then I could not see the man who
was crouched at the entrance, and
the circumstances seemed to indicate
that nobody was home.
Therefore, when I jumped on
the deck, and started towards
the stern, I was startled by a voice coming from my right
hand side shouting – “What are you doing on my boat?”

My error is understandable. At the time
of these events, I did not know that
people do not leave their houses
unattended in Brazil. If somebody is
stupid enough to leave his house without
a guardian, theft is certain, and invasion
followed by squatting is very likely.
I cannot resist the temptation of
comparing Brazilians with Russians
in this particular. When I studied
at the Bauman University, in Russia,
I knew Victor Bojarczuk,
a mathematician whose
parents and brothers lived somewhere
in Siberia.

When the Bojarczuk family traveled
to a far away town, in order to buy
supplies and tools, Mother Bojarczuk
would prepare non perishable food
and fuel for heating. Therefore,
if a traveler should get lost in
those vast frozen expanses, he would
find a welcoming abode, a refuge,
which would protect him from the
cold, through providing
firewood, food and water.
Mother Bojarczuk did not hope
for gratitude from the men and women
that she helped along her life.
It is a fact that many men, women and even children
enjoyed the anonymous hospitality
of the Bojarczuk family and other
Russians that share these beautiful
traditions and practices.
But Mother Bojarczuk never met
any of these persons that she saved
from a horrible and
almost certain death. On the other hand,
Victor told me that his family never
missed anything of value that they left
in the house. Travelers would eat
the food, use the firewood, sleep
in the beds, but would not steal
a thing. Since I don’t want to
leave this behavior without witness
and mention, I will list here the
names of some people who are members
of the Bojarczuk family: Leon, Victor,
Nina and Tom.

The deck of the flat bottomed boat
sat only 2 feet above the water level.
Therefore, the design of the ship
made it easy for me to
throw my medical bag
over the rail, and raise myself
onto the bow deck. There, I quickly
recovered my medical
bag, and started to
walk friskily towards the stern. As I said
before, the ship master’s voice
stopped me abruptly in my tracks:
“What are you doing on my boat?”.

The man, to my reckoning,
was about fifty years old.
However, it is hard to know
the exact age of
people who live in that region of
Brazil by appearances,
as their skin
is marked by wrinkles and grooves.
These deep skin furrows
can be explained both through old age,
or constant exposure to
the hot tropical sun, which
also accentuates skin grooves.

If natives from northern Brazil
were there with me in front of the
boat dweller, they would not be able to say
for sure whether that man had ancestors
among South American Indians,
Africans or Europeans, but his forefathers
certainly came from one of these parts
of the world. In Brazil, the climate
and the methods used to earn a living
have deeper influence on the phenotypical
aspect than does ethnic origin.

The boat dweller had a length
of tobacco, which looked like
a thick piece of rope.
This he was chopping very finely
with a curved knife.
The making of straw cigarettes from
rope tobacco is
very popular among Brazilian men who
live in the country side. The behavior of
chopping tobacco is relaxing, and
this psychological addiction
adds to the effect of the nicotine.
In fact, many Brazilians claim
that they managed to get rid
of the habit of smoking,
but they could not
stop tobacco chopping and
hand rolling straw cigarettes.
An important component of the
behavior is to perform tobacco
chopping while crouching on one’s heels.
Researchers observed that chopping tobacco and
hand rolling straw cigarettes consume
so much time that country side
Brazilians end up smoking moderately.
At least, if one has to chop tobacco
and hand roll one’s
own cigarettes, chain smoking becomes
impossible.

When I mentioned the curved knife
that the Brazilian boat dweller was using
to chop tobacco, the reader certainly
imagined some kind of weapon similar
to the Turkish scimitar. However, the
tobacco chopper’s knife did not have
the cutting edge on the outer part
of the blade curvature. The
edge of the Brazilian knife is
in fact found within the curved blade.
A good way to imagine this knife
is as a cutting hook.
The ship master did not wait for me
to arrive at any conclusion as to
the goal of such a knife design.

“What are you doing on my boat?
I will answer this question myself.
You thought that I am an old man,
therefore you can enter my house,
steal my property and kill me in
the process, if necessary.
After that, you would probably
rape my granddaughter.
But I have something to tell you.
I may be stronger than you, or
perhaps you are stronger than me.
In any case, do you see this
hooked knife? Do you know why
it has a cutting edge curved to
the inside? I will answer you this
question as well, for you do not
seem to know local customs.
In my land, that you are visiting,
one uses this kind of knife to
castrate pigs. The curvature hooks
around the testicles, and all one
needs do is pull on the knife,
in order to complete the task.
Since you are a curious man,
you certainly have another question.
Why do I need such a long knife
for castrating piglets? The fact is
that this knife has two functions.
The first one is to castrate pigs,
as I already made clear. The other
one is to gut intruders. I am a civilized
fellow, and do not usually castrate
men before gutting them. However, I
may make an exception in your case,
since you certainly intended to
rape my granddaughter. In this special
circumstance, castrate before killing
is not an unusual or cruel punishment.”

I tried to show myself as being
calm and
collect in light of the circumstances
I now found myself in, while replying to
the long diatribe of the boatman.
“You are mistaken, my friend. I am not
a thief, murderer or rapist. All I want to
do is to go around that mob over there.
That is the only reason for my entering
your flat bottomed ship.”

At this moment a girl came out of the
cabin. She was the granddaughter of the
old man, to be sure. She was wearing
a sooted dress, which was white
at some point in time. However, the girl
often held and shook it over an
open flame in
order to kill fleas and ticks.
The girl’s hair was tangled and
dirty. She was holding a rag doll, which
had lost the two arms and one leg.
The doll’s skirt was also gray
with soot, just like the girl’s dress.
I guess that the girl held and
shook the doll over the fire,
in order to kill imaginary ticks.
Another possibility is that she
used her old clothes to make skirts
and dresses for the doll.

Suddenly, the girl spoke.
“Grandfather, after killing this bad
man, and before throwing the body into the
river, cut his hair off for me. I need it
for Rachel’s wig. The hair of the other
bad man, which I sewed to my doll’s
head has almost entirely gone.”

The old man answered the girl:
“I am not sure whether this man is
really evil. After all, he has not
hurt you or me. Of course, I don’t know
what he would do, given the chance.
For the time being, he is only a
trespasser. Anyway, my dear,
I still have not had
the time to interrogate this individual,
as to whether he did not attack us for
lack of opportunity or for not being
of violent intent.
In the latter case,
I will give him a speedy death
by cutting his throat,
and throwing his body over the rail.
Besides this, if he is only a trespasser or a mere
thief, I don’t intend to mutilate his face
or defile his body. But if he is a rapist
or a murderer of children, then I
need to make him an example for
others with like character.
A rapist deserves to be gutted
and lay in agony on the deck
before being thrown into the river.
Whatever is my decision, I think
you should enter the cabin. You are
too young to witness an execution.”

At this moment, I felt the need
to interrupt this not so delicate
conversation between this loving grandfather
and his lovely granddaughter. This was not
due to my having any preference concerning
the methods proposed for my death,
but purely to gain some time.
“I ask you, dear Sir, do not try to
cut my throat, because I don’t think
I deserve dying so young. I am a doctor,
a physician. I was born in the United States,
a country where doctors are held in high esteem
and usually do not get involved in crimes.
On the contrary, they are always ready
to help people. For instance, you have
a skin condition that I suspect to be
basal cell carcinoma. In simple terms, you
have cancer, but not a dangerous
and aggressive kind of malignancy.
I can heal you.”

The talk about cancer was contrived
in order to gain time. I could not
diagnose cancer through a glimpse
from two meters away, let alone
classify the disease as basal cell
carcinoma. However, if the man
were to buy my talk, I could fake a
medical procedure and try to
win his good will. At the very least,
I could divert his attention long
enough for a quick escape. Unfortunately
he seemed too stupid to understand
the meaning of carcinoma. Anyway,
without waiting for his reaction
to my words, I kept my eyes on him,
while stepping backwards, in the direction
of the stern. However, I was so unfortunate
that I tripped on that kind of step
produced through those differences
that often exist between the prow
and the stern of a deck.
I tripped and fell on my back.

The first thing that a retreating person
thinks when she or he falls back is to
prop on both hands to get up. This
strategy is dangerous, since it
precludes the use of hands for
defense or attack. Therefore,
practitioners
of Brazilian Jiu Jitsu developed
techniques for taking the fight to
the ground. I learned these
techniques while still at Logan,
but they proved to be ineffective
on this particular occasion,
since my opponent
did not make any gesture
towards attacking me. He merely shouted
orders to his granddaughter.
“Darling, could you bring my
shotgun here? It is fixed on
the wall, above my bed.”

Masters of Brazilian Jiu Jitsu
never told me anything about
shotguns. Then I forgot their
excellent lessons, turned
by back to the boat dweller,
raised on my foot and started
the six meters that separated
me from the stern. Of course,
I am not sure about the distance
that separated me from the stern
and safety. Probably I would not
be safe even after jumping out
of the boat, since the crowd
in front of the movie theater
could side with the boat dweller.
In any case, when I was making
the final steps to the stern,
my way was interrupted by the
presence of two uniformed men
blocking my way.

The policemen seemed to be more
interested in the boatman
than in me. Therefore, it was to
my enemy that one of the policemen,
a tall European looking fellow, said:
“So, did you kill
the Bolivian? I mean, the
Bolivian policeman who was found
floating down the river, with
large patches of missing hair.”
The other policeman, a short
and stout mulatto complemented
the thought: “I wondered who
would kill a man to steal his
hair. Now I have a good explanation
for the event.”

One thing that I learned from Brazilians
is to trust policemen less than
gangsters. Therefore, while the
two policemen were interrogating
the boatman, I started to walk
around them in order to escape
from that ambiguous situation,
where I could not tell the intent
of the new arrivals.
But the stout mulatto tried to interrupt
my get away. “My partner and me,
we just saved your balls and maybe
your life. Aren’t you going to
show your gratitude?”
I was in Brazil long enough to
know how to show gratitude,
therefore I asked: “How much
do you want?” The response of
the police officer did not
help to make the negotiations
advance: “How much do you have there?”

At that moment, I saw Pülowi standing
by the door of a car and frantically
signaling me.
I did not give further heed to
the two policemen, and reached
for the low rail around the stern,
jumped to the sidewalk, and
ran to the car. Pülowi entered
the car ahead of me, slided on
the seat over to the other side.
With that movement, she left
the open door ready for me
to enter the vehicle.
As soon as I was half sat,
the driver accelerated the
car so fast that the door
closed on its own inertia.

Pülowi started a conversation in
Russian to keep me a par
of developments.
“I guess you speak Russian,
as I saw you reading a
novel by Boris Akunin on
your Kindle. When I hired this fake
taxi driver, I pretended not
to know Portuguese
or Spanish. Therefore, when he hears us
speaking Russian, he probably
will think that we are conversing
in an Indian language, such as
Quechua. I would doubt very much
that he can tell
the difference between Russian and
Quechua. The point is
that we are not safe yet,
since this man clearly intends
to steal your money and
rape me. He avowed these
plans to his companions,
since he thought that I
could not understand what
he was saying. Therefore,
whatever he does, don’t react.
Let me handle the situation.
My job is to get you safe
to Raposa do Sol, so don’t
let your amateurish maneuvers
make this task harder than
it already is.”

The street along the banks of the river
ended at a glade that grazing animals
had cleared in the forest. The driver
stopped the car and told me: “Start walking,
leave the little Chinese girl entrusted
to my care.” People in Brazil often
confuse native Indians with Chinese
or Japanese, since they display
oriental features.

The assassin spoke in coloquial
Portuguese, when he made the suggestion
that I should depart and leave Pülowi behind.
However, he was not sure that
I could understand Portuguese. Therefore
he made his meaning clear with a Glock pistol
that he brandished,
using the weapon to make a gesture
in the direction of a single line track
that penetrated into the forest.

I am not brave enough to face
an armed drug trafficker. Even so, I
did not hide myself in the
forest, as the fake driver
suggested. In fact, I stayed
put, in doubt about what
to do. Even if I would be
coward enough to run into
the wood, after raping the
girl, the ruffian would
remember that I could be
carrying money. In that case,
he would chase me and kill
me easily, since he knew
the land. Evasion was not
a good option for an
intelligent coward, like myself.

After suggesting me the way into
the woods, the bully focused
his attention on Pülowi. Initially,
he pointed the gun on her head,
in order to bend the girl to his will.
Then he probably concluded that a gun was
an excessive resource for taming
a young woman, and it could get
in his way during the rape. I could
infer that the man concluded that
a gun was not necessary for the
task at hand, because
he dropped the pistol on the ground.
I immediately thought that an opportunity
could arise, where my taking hold of
the pistol could be attainable,
when the rapist started
doing what rapists do best.

I cannot remember what plans I had created
in my mind for wrestling the gun away
from the thug. In any case, my plans
did not come to bear. As soon as the rapist
dropped his pants, the girl drew
a knife from a sheath on her lower left
leg and cut his penis off. The
proceeding stage of Pülowi’s master
plan was to get
hold of the gun. Upon doing so,
she liberated the
wounded man from his misery
by shooting him in the head.

I followed the wild woman in
silence to wherever she wanted
to lead me. We followed the
river downstream through the
dense forest until we found a
motorized boat hidden among the canopies
of the low lying trees
that grew on adjacent swampland.
It seems that Pülowi left
that boat there a few days
before for the sole purpose
of providing us a quick getaway.

Pülowi piloted the boat
to a much bigger town, with
well constructed and conserved
buildings. There were many
warehouses and illegal sawmills
built in their essence from
premolded concrete. The Indian
girl guided me to a two floor
office facility. Only one of
the offices was occupied, and
even here there was a lone
middle aged man, who was sat in a very
comfortable chair behind a desk.
The girl and me stood, as
there were no additional chairs for
possible visitors.

The Indian girl told the
owner of the establishment:
“Here is your man, safe and
sound as I had promised you.
I hope that my payment has
been transfered to my account
in Colombia.”

“I still need your services,
young woman,
and as long as I need you,
be rest assured that I will
deposit your money as
agreed. Do you need ready
cash for your trip back home?”

“I am not crazy enough to
carry cash on me in such
a place. When I need something,
such as food and tools, I
prefer to steal or rob,
instead of drawing attention
to myself by paying in cash for
an item and showing everybody
that their attack on me
could be profitable.”

“Since you are satisfied
that matters between us
are settled, you can leave
me with the doctor to
talk business.”

I thought that the man
behind the desk was some
sort of government officer
in charge of administrating
the Indian reservation.
Therefore, I asked him
when I would depart for
the Indian village, where
I was supposed to work.

“There is no Indian village.
In fact, there is no Pirunucu
tribe. The bureaucrats in Brasilia
created many fictional towns
and villages for bogus medical
positions. Politicians and
fake entrepreneurs keep half
of the payment that should go to
the doctors in charge of inexistent
practices. The doctors themselves
receive the other half for doing
nothing, which is a good deal
for everybody!

“Creating fake ids or borrowing the
id from a dead person is a common
practice in Brazil. For instance,
crooks often claim that a deceased
person is alive to collect benefits from
social security or medical insurance companies.
In practice, long after the death of the client,
hospitals and lawyers keep collecting
pension checks, benefits and payments
for providing health care.
The case of Mais Medicos is interesting,
because the swindlers have created
whole tribes, towns and cities for
embezzling money. However, this
is by no means the largest
scheme for stealing public money!
For example, the supplying of
water to urban populations
provided interesting opportunities
for corrupt politicians to
rake off some good cash.

“The most notorious case of such
schemes to earn money with water
transference projects, which in fact
deliver little
or next to nothing of the promised
resource, is the transference of
water from the San Francisco River
to smaller streams in the Northeast
of Brazil. The civil engineering works should
have taken at least 10 years.
The fake engineering firms
asked for two billion dollars in small
installments for completing the project,
only to revise the value upward to 4 billion,
when arriving at the deadline of completion.
It is pointless to say that at the
deadline there were no channels
to speak of. The make-believe
engineers counted on time for
removing the necessity of accountability:
In ten years, honest engineers and
politicians involved in the project
would be dead from natural causes,
killed or removed from the political
process, and the surviving engineers
and corrupt politicians
would have time for making the
money untraceable. The other possibility
is that the incumbent government would go bankrupt
and stop paying the installments,
which would provide a good excuse
for interrupting the works,
thus keeping the amount already paid.

“In this town of ours, the world
and his wife are organizing
schemes for accumulating wealth.
There are people who are chopping
down the forest to obtain wood,
which will worsen global
warming, but not before making
the criminals rich from selling
the wood to furniture manufacturers
in Denmark. There are also people
that are mining gold in the Indian
reservations, which is by the way illegal.
I represent the miners and panners.
Since I am not half as bad as many of the
criminals here,
I saw to it that the Indians
receive their fair
share of the criminal operation.
I am talking about real Indians,
flesh and blood human beings,
not imagined tribes, such as
the Pirunucus. These Indians
do need physicians and dentists,
and have the money to pay
you. What do you think about
working for my Indians? Not that
I care about these Indians, but
they have low immune resistance to
European infectious diseases. If
all of them die from the contact with
civilization, squatters will occupy
their land, and I will not have
the monopoly of buying the gold
that belongs to them.”

“If what you are telling me is true,
I am involved in a criminal scheme,
and I will denounce it to the
authorities.”

I must reveal a few things about
myself. The first revelation is that
I am not like Archie Goodwin. This
means that I cannot reproduce a
conversation verbatim. For those of
you who do not know who is Archie
Goodwin, Rex Stout wrote many
books about an old man,
Nero Wolfe, who was so fat that
he rarely left his brownstone
house voluntarily. Therefore,
he spent a lot of
money to make his home amenable
to all his needs, hobbies,
desires, impulses and cravings.
One of his passions was eating,
the other was orchids, in that order.
Therefore,
he hired a Swiss chef and a German
gardener. Of course, the Swiss chef
was born in that region of Switzerland,
where the locals speak French. It was in
French that Nero Wolfe discussed
the everyday menu with Fritz,
this is the name of the Swiss chef.

In September 1934, Nero Wolfe left his home
willingly for the privilege of
dining at the same
table as Albert Einstein. I guess that
he accepted the invitation not
because he would sit with Einstein,
but because the food was good.

How could Nero Wolfe manage to sustain
such an expensive life style?
Well, he owned a detective agency,
where the only fixed employee
was Archie Goodwin.
The peculiar ability of Archie Goodwin
in repeating conversations verbatim
came to my mind because the
top of the desk was full of
books on Nero Wolfe. The man
in front of me
certainly was fond of tales
about the obese bon vivant. However,
let us return to that strange office
with only two pieces of furniture,
a desk and a chair. Before this
long digression, where I explained
who Archie Goodwin was, this report
came to a stop
at the point, where I was
strongly putting the case to my host of
the need to inform
the authorities about this scheme
for hiring fake physicians.

“I repeat, it seems that
I became one of the victims
of a criminal scheme
for hiring unscrupulous doctors.
The authorities must be told ofthis embezzlement of public funds.”

“From your choice of vocabulary,
gestures and tone of voice,
I got the impression that you
believe that I am part of these
criminal activities. I can also
infer that you are a newcomer
to Brazil, since you believe that
the local authorities are engaged
in crime fighting operations in
the broader sense.
This may be true, if the criminals
are disrupting crimes committed
by the authorities themselves,
such as corruption, misconduct,
passing legislation without
rising above self-interest,
overpricing, report falsification
and fake bids. I could keep on listing
the different transgressions of the
laws of the land and crimes against
humanity that Brazilian authorities
have devised to increase their income
or for a comfortable retirement plan
in Paraguay. Unfortunately, I am
not sure whether the English language
has all the technical words for
describing the variety of unlawful
acts that Brazilian public officers
commit on a daily basis.

“You need to wise up. For instance,
did you notice that there is no
chair for visitors in my office?
The reasons for a person
coming to me are many. Very few
people enter through that
front door, in order to propose
a mutually beneficial deal, but
given the opportunity through a
lapse on my part, they will force
the tide to turn in their favor.
A slightly larger class
of callers want to profit
at my expense. Finally, there
is a large group of men and
women that appear
with the clear intention
of killing me or taking me
for everything they can.

“In any case, when you say that
you will report the misappropriation
of public funds, you sound as
you were threatening somebody.
Since I am the only person in
this room, it seems as though
your threat is aimed at me. The fact is
that I have nothing to do with
this health scam. I found out
that it existed through pure chance.
When people in Brasilia discovered that
you would come here to take up a doctor’s
position for an inexistent tribe,
they decided it would be best to kill you,
since you could call
public attention to what they
are doing. As things stand,
the criminals do not
have operatives in this part
of the country, and so they contacted
my cousin Pafuncio to do the job,
who subcontracted me. I don’t know
what I would do if the amount paid
were large enough. However, I am a little
soft and sympathize with your predicament.
Therefore, I am proposing a deal,
where you will do exactly what
you intended to do at the start
of your long wending journey to this place,
to wit, provide health services
to an Indian tribe.”

“Sorry for being rude. I guess I
will accept your offer for no other
reason than to discover a way for
returning to civilization.”

“I don’t know why this place cannot
be considered as civilized.
Perhaps because people here prefer
to do business with Indians,
instead of exterminating them
with the intent of bringing a
doubtful brand of civilization.
Don’t worry. You won’t find
civilization in the abstract
sense of the word, but you
will enjoy all benefits of
civilization. In the restaurant
downtown, you can drink French
wine, eat ratatouille and
hear La Vie en Rose on an
old jukebox. Sorry, the waiter
does not speak French, only
the whores do. I am not sure
whether our health service is
as good as in Paris, but providing
health care is your job,
isn’t it?”

At that moment, a blond young woman
appeared behind me and poked my
ribs with the muzzle of a handgun.
Since I was not
expecting an interruption in
that strange conversation,
hearing a voice behind me
coupled with the poke in the
ribs, really gave me a fright.
The official, at least, let’s
call him that, explained the
situation, both to calm me
and prevent the new arrival
from becoming overly protective
by shooting me.

“Sorry, Doctor. I
called Ms Anita Nikolaisen,
who will show you your
accommodations, and teach you
the basics of Nheengatu,
that is the language spoken
by the tribe where your
practice will be located.
To make sure that I
receive what is due
for my intermediary services
over this
whole arrangement, the
hired doctor, in this case you,
should double as my
interpreter in my dealings
with the council that
governs the Indians.
Therefore, it is important
that you learn at least
some Nheengatu with the help
of Ms. Nikolaisen.”

After signaling to
the blond woman that everything
was fine and that I posed
no threat, the man continued
his rambling.

“Since I couldn’t imagine a
better way of calling Ms. Nicolaisen,
I pressed the panic button under
the top of my desk. When
Anita hears the signal from the
panic button, she enters my
office shooting. I raised my
hand, as a signal for her
not kill you. The hand signal
sometimes works as intended.”

Anita continued the explanation,
giving her side of the whole
episode, as an excuse for
her behavior toward me.

“The problem is that I did not know
anything about the signal. When I
received the panic signal, I thought
that we were under attack. I entered
here ready for shooting. What is your
name? Well, Mr. Jensen, I refrained
from killing you, not because of
Mr. Rafael’s raised hand. For one thing,
I was afraid that the bullet could
hit my boss, after going through
your body. Besides this, I don’t
know what you carry in this
suitcase, but it may be a bomb
ready to explode if you drop
dead and release a possible trigger
that you keep pressed while you are
alive and conscious. While the terrorist
keeps such a trigger down, the bomb does
not explode, but if an agent of law kills
the fanatic, he automatically releases the
trigger, and the bomb goes off.
I heard that Islamic fundamentalists
rely on such a device.”

“Now that I have learned of
my narrow escape from death,
let us discuss my wages.”

“I am afraid you didn’t understand
what is going on. My business is
not health care. I do not run a
charity institution. I am a
racketeer. The contract is very
simple: You pay 20% of every
penny you earn in the Indian
Reservation. The value is so
low, because you are going
to render me invaluable services
as an interpreter and bookkeeper
of the gold extracted from the mines.”

“Then, how will I earn my money?”

“That is a good question. Should
I answer that this is your problem?
You bet I should! However, since
you are a foreigner unaccustomed
with the practices of the land,
I will elaborate on the standard
answer. The Indians have their
share of the valuable minerals
extracted from their land.
Therefore, they can pay your
fees. Then you have the gold
diggers, that are stabbed from
time to time. If you save the
life of a stabbed man, or a
shot man for that matter,
you can send him a fat bill.
When I say send a fat bill,
I don’t mean really send a fat bill.
Brazilian miners carry their valuables,
such as gold nuggets, precious stones
and even foreign currency in
their underpants. Everybody knows
that. Therefore, at airports,
the first thing that a customs
officer checks are the underpants
of any individual suspected
of smuggling money
from one place to the other.
Even though most people
know where the valuables are,
nobody steals from a wounded
miner. Except his doctor and
nurses of course. If you save
the life of a man, you can collect
some 70% of his belongings
as fee. Please, collect at
least 20%, that is my part
of the deal. Leave him with
30% of his money or gold
nuggets, for the trip back home.

“There is another way of
making your stay in Brazil
profitable. From time to time,
French cosmetologists come
to this particular region
of Brazil to buy raw material
for soaps, perfumes and the
like from the Indians.
You can intermediate the
sale of such products
and realize a sizable
amount of euros. Don’t
forget about my 20% here
as well.”