Into Python

And beyond

To understand new experience, we need to know where we are. So, before I go into my experience with Scheme, let’s start with Python and why it’s awesome:

“Pseudocode with one right way to do it and hackable, scalable batteries.” — Arne Babenhauserheide

Pseudocode which runs

for address in addresses:
  print address

One way to do it

import this

Hackable, but painfully

def hello():
  """Greet the World.

  >>> hello()
  Hello World!
  """
  print "Hello World!"

# preparation: Get a function without context
from math import log
# get the module name
modulename = log.__module__
# import the module
mod = __import__(modulename)
# get the filename. Use dir(mod) to find out what you can do.  
# Or use tab-completion in the python-shell 
# (if you enabled GNU readline - if you did not: 
# Best enable readline right now!)
filename = mod.__file__
print filename
# here this gives /usr/lib64/python2.7/lib-dynload/math.so

Batteries and Bindings

import antigravity

Scales up

With all its strengths, Python is still a language with a limited syntax. It is very broadly applicable, but it has strict rules how things can be done. These rules create a straightjacket you cannot escape easily. Most of the time, they are convenient, and they can help when you develop code in a community. But regardless of the chains you choose, they can never be convenient for all tasks. And whatever the task, when you go deep enough, even golden chains hurt.

The warped mind

Templates condemn a language

if __name__ == "__main__": 
   # run the script

Python syntax reached its limits

if x:
    a = 1
else: 
    a = 2

a = if(x 1 2)

a = 1 if x else 2

a = (1 if x else 2)

(define a (if x 1 2))

direction = [(math.atan(v[1]/u[1])
              if ((v[1]*u[1] > 0) and not v[1] < 0) else 
              -math.atan(v[1]/u[1]))
             for u, v in zip(mfu, mfv)]

Complexity is on the rise

def deco(fun):
    return mun

@deco
def mun():
    print ("Welcome to compile-time breakage!")

def mun():
    print ("We have to introduce a proxy.")

@deco
def proxy():
    pass

Time to free myself

So I started looking into other programming languages. I had two main contenders:

• Fortran, the tried and true tool for engineers, and
• Scheme, the academic branch of the Lisps.

I started with Fortran as the pragmanic choice for a physicist, but soon I caught myself replicating every Fortran-experiment in Scheme. So I decided to follow my gut and dive into Scheme. From there on, the choice was easy: There are several Scheme implementations - and one of them is from the GNU Project: Guile.7, 8 But before really starting with that, I read The Adventures of a Pythonista in Schemeland (PDF) by Michele Simionato.

It is half a year later, and Scheme now feels natural to me. Actually more natural than Python.

The expressiveness of the original syntax of Python was a bit too limited, and this caused the language to hatch a new syntax which makes the whole of Python much more complex. There is no longer a simple uniform syntax, but two complementary styles with different structures. It is still very easy to understand and I think that it set a new standard for readability of code - so in that aspect the Python experiment was a phenomenal success - but it is starting to break down as people expand it into more and more directions.

Guile Scheme on the other hand can accomodate new functionality much more easily. And from the intuitive side, I now see commas between function arguments and they feel like needless bloat. My gut suddenly says “leave out the commas!”, and I find myself forgetting them in Python-code. I think the commas once looked useful to me, because languages with commas helped me get rid of the quoting hassles in the shell, but now there’s a language which does not require commas to achieve that goal - and stays clean. That sounds small, but it changes radically how the language feels.

But the (parens)!

(for 
 ((beginners (readability of parens))
  (is horrible)))

for 
  : beginners : readability of parens
    is horrible

./configure; make check;
guile -L . --language=wisp

Summary

After having listed the many strengths of Python, it’s time for a very unfair comparison: How does Guile Scheme stand against the strongest aspects of Python?

I ask this, because it is what Python-Programmers will ask - and because it is what I asked myself when looking into Guile Scheme.

Later we will see where Guile Scheme enables us to go beyond Python. But now: Let’s start the race.

Pseudocode

;; this example needs foof-loop installed via guildhall!
;; see https://github.com/ijp/guildhall/wiki/Getting-Started
use-modules : guildhall ext foof-loop

;; Pseudocode adapted from 
;; http://en.wikipedia.org/wiki/Pseudocode#Syntax
define : divisible? number divisor
         = 0 : remainder number divisor

define : fizzbuzz
  let : : print_number #f
    loop : : for i : up-from 1 : to 100
        set! print_number #t
        when : divisible? i 3
               display "Fizz"
               set! print_number #f
        when : divisible? i 5
               display "Buzz"
               set! print_number #f
        when print_number
               display i
        newline

fizzbuzz

for i in [1, 2, 3, 4]:
    if i >= 4:
       continue
    def counter():
        if i != 2:
            for j in range(i):
                yield j
    print list(counter())

for k in (range(i) 
          if i != 2 else []
          for i in [1, 2, 3, 4]
          if i < 4):
    print k

a = 1
b = 1 if a != 1 else 2
c = (1 if b > 2 else 3)

use-modules : guildhall ext foof-loop

loop : : for i : in-list '(1 2 3 4)
         if {i < 4}
            let : : k : cond ((not {i = 2}) (iota i)
                             (else '()))
                    display k

do : : i 1 : 1+ i
   : > i 4
   display i

let : : i 1
  while : < i 5
          display i
          set! i : 1+ i

let loop
  : i 1 ; the initial value
  when : < i 5
         display i
         loop : 1+ i

for : i in '(1 5 8)
      display i

let loop
  : l '(1 5 8)
  when : not : null? l
       display : car l ; first element
       loop : cdr l ; continue with rest

names = [name for ids,name in results]

define names : list-comp name for (ids name) in results

use-modules : srfi srfi-42
list-ec (:range i 5) i ; [i for i in range(5)]
; => (0 1 2 3 4)

;; this example needs foof-loop installed via guildhall!
;; see https://github.com/ijp/guildhall/wiki/Getting-Started
loop : : for element : in-list list
  display element

;; this example needs foof-loop installed via guildhall!
;; see https://github.com/ijp/guildhall/wiki/Getting-Started
loop 
  : for x : in-list '(1 2 3)
    with y 0 {y + {x * 2}}
  . => y

One way to do it?

use-modules : 2d agenda
              2d coroutine
              2d game

coroutine
  while #t
    walk 'up
    wait game-agenda 60
    walk 'down
    wait game-agenda 60

define : call-with-coroutine thunk
  . "Apply THUNK with a coroutine prompt."
  define : handler cont callback . args
    . "Handler for the prompt. 
       Applies the callback 
       to the continuation (cont) 
       in a second prompt."
    define : resume . args
        . "Call continuation 
           that resumes the procedure.
           Uses the continuation 
           from the handler."
        call-with-prompt 'coroutine-prompt
              lambda () : apply cont args
              . handler
    ; here the handler 
    ; calls the callback with resume
    when : procedure? callback
        apply callback resume args

  ; finally call-with-coroutine 
  ; calls the code (thunk).
  call-with-prompt 'coroutine-prompt 
                  . thunk handler

; definition of the coroutine macro.
; Enclodes the code in a function (lambda)
define-syntax-rule : coroutine body ...
  . "Evaluate BODY as a coroutine."
  call-with-coroutine : lambda () body ...

define-syntax-rule : coroutine body ...
  . "Evaluate BODY as a coroutine."
  call-with-coroutine : lambda () body ...

define : call-with-coroutine thunk
  . "Apply THUNK with a coroutine prompt."
  define : handler cont callback . args
    . "Handler for the prompt. 
       Applies the callback 
       to the continuation (cont) 
       in a second prompt."
    define : resume . args
        . "Call continuation 
           that resumes the procedure.
           Uses the continuation 
           from the handler."
        call-with-prompt 'coroutine-prompt
              lambda () : apply cont args
              . handler
    ; here the handler 
    ; calls the callback with resume
    when : procedure? callback
        apply callback resume args

  ; finally call-with-coroutine 
  ; calls the code (thunk).
  call-with-prompt 'coroutine-prompt 
                  . thunk handler

Planned Hackablility, but hard to discover…

import math
dir(math)

module-map 
  lambda (sym var) sym ; return the symbol (key)
  resolve-interface '(ice-9 popen)

define oip : @ (ice-9 popen) open-input-pipe

define oip
  module-ref 
    resolve-module '(ice-9 popen)
    . 'open-input-pipe

if __name__ == "__main__":
    print "you executed", __file__

(define (my-local-main)
  (display "I am just a dummy, why do you call me?"))
(let ((my-local-name (module-filename
                      (program-module my-local-main))))
   ; catch the case when the compiler
   ; optimized away the info.
  (when (or (not my-local-name)
            (string-suffix? (car (command-line))
                            my-local-name))
    (display "you executed this as script.")))

#!/bin/sh
# -*- scheme -*-
exec guile -e main -s "$0" "$@"
# Thanks to exec, the following lines 
# are never seen by the shell.
!#
(define (main args)
  (display "Horaay!\n"))

#!/bin/sh
# -*- scheme -*-
exec guile -e '(@ (py2guile runscript) main)' -s "$0" "$@"
# use @@ if your module does not export main
!#
(define-module (py2guile runscript) 
                #:export (main))
(define (main args)
  (display "Horaay! Module! Horaay!\n"))

#!/bin/sh
# -*- wisp -*-
exec guile -L $(dirname $(dirname $(realpath "$0"))) \
     --language=wisp -e '(@ (py2guile runscript) main)' \
     -s "$0" "$@"
# use @@ if your module does not export main
; !#
define-module : py2guile runscript
              . #:export (main)
define : main args
  display "Horaay! Module! Horaay!\n"

#!/usr/bin/env guile
!#
(define (main args)
  (display "Horaay!\n"))
(main 1)

#!/usr/bin/guile \
-e main -s 
!#
(define (main args)
  (display "Horaay!\n"))

for script in runscript-shell.scm runscript-dash.scm \
              runscript-env.scm runscript-meta.scm; do 
    echo $script; ./${script} >/dev/null;
    time for i in {1..1000}; do 
       ./${script} >/dev/null;
    done;
done

for script in runscript-shell.scm runscript-dash.scm \
              runscript-env.scm runscript-meta.scm; do 
    echo real $script; ./${script} >/dev/null; 
    for i in {1..1000}; do 
        time ./${script} >/dev/null; 
    done;
done 2>&1 | grep real | sed "s/.*0m.*\\.0//" | sed s/s$//

#!/usr/bin/env guile
-*- scheme -*-
!#
; This code will run the main function of the file it is given 
; as argument. This keeps the testing logic inside the project 
; while keeping the overhead for each module to a minimum. 
; Thanks to Mark Weaver for this code!
(use-modules (ice-9 match))

(match (command-line)
  ((_ file args ...)
   (primitive-load file)
   (let ((main (module-ref (current-module) 'main)))
     (main args)))
  ((cmd . _)
   (format (current-error-port)
           "Usage: ~a FILE [ARGS ...]\n"
           (basename cmd))))

#!/bin/sh
# -*- wisp -*-
exec guile -L $(dirname $(dirname $(realpath "$0"))) \
     --language=wisp -e '(@ (py2guile runscript) main)' \
     -s "$0" "$@"
# use @@ if your module does not export main
; !#
define-module : py2guile runscript
              . #:export (main)
define : main args
  display "Running you Module!\n"

from math import log
log.__module__ # it is math
import math
print math.__file__ 
# this code prints /usr/lib/python2.7/lib-dynload/math.so

from math import log
print __import__(log.__module__).__file__
# this code prints /usr/lib/python2.7/lib-dynload/math.so

use-modules : system vm program
              (ice-9 popen) #:select : open-input-pipe
; then regain the module path
display : module-filename : program-module open-input-pipe
newline ; this code prints ice-9/popen.scm

map 
  lambda : x ; lambda is an anonymous function. 
             ; In code you can also use the lambda-symbol, 
             ; but it breaks my latex export.
      let*
       : sep file-name-separator-string
         path : string-join (list x "ice-9/popen.scm") sep
       if : file-exists? path
          . path
  . %load-path

; define the module
(define-module (inm)
  #:export (inm in=m))

; get introspection capabilities
(use-modules (system vm program))
; define a syntax rule.
(define-syntax-rule (in=m body ...)
  (lambda ()
    (define (my-local-main)
      (display "I am just a dummy, why do you call me?"))
    (let ((my-local-name 
           (module-filename (program-module my-local-main))))
  (when (or (not my-local-name) ; catch the case 
                                ; when the compiler
                                ; optimized away the info.
            (string-suffix? (car (command-line)) my-local-name))
         (begin body ...)))))
; the lambda is executed here, not in the macro!
((in=m (display "you executed inm.scm as script")
       (newline)))

(define-module (in))

(use-modules (inm))
((in=m (display "in.scm")))

(use-modules (in))

Batteries and Bindings: FFI

use-modules : system foreign
; load the netcdf library.
define libnetcdf : dynamic-link "libnetcdf"
; get the function to inquire the netcdf version.
define nc_inq_libvers 
    pointer->procedure 
      .  '* ; returns a pointer to a char-array.
      dynamic-func "nc_inq_libvers" libnetcdf 
      list ; takes no arguments (empty list)

; test the foreign function 
; and convert the returned char-array to a string.
pointer->string : nc_inq_libvers
; => "4.1.1 of Jul  1 2013 03:15:04"

Does it scale up?

use-modules : ice-9 optargs
define* 
    example required1 
          . #:optional opt1 (opt2 'opt2default) 
          ; optional must come before #:key!
          . #:key named1 (named2 'named2default) 
          . . rest
    display 
        list 'required1: required1 
             . 'opt1: opt1 'opt2: opt2 
             . 'named1: named1 'named2: named2 
             . 'rest: rest

example 'foo #:named2 'bar 'baz
newline ; prints (required1: foo opt1: #f opt2: opt2default 
        ;         named1: #f named2: bar 
        ;         rest: (#:named2 bar baz))

use-modules : ice-9 popen

use-modules 
  : ice-9 popen
    . #:renamer : symbol-prefix-proc 'popen-

use-modules 
  : ice-9 popen
    . #:prefix popen-

use-modules
  : ice-9 popen
    . #:select : (open-pipe . pipe-open) close-pipe

(define y 5)
(define-syntax x
  (identifier-syntax (var y)
                     ((set! var val)
                      (set! y (+ 1 val)))))
(write x) ; -> 5
(set! x 5) 
(write x) ; -> 6!

Summary

Guile Scheme is a solid language, and it can compete quite well with Python, even in the areas where Python is strongest. But there are some dark corners I did not mention yet. Here I will explore the worst shortcomings I found in Guile Scheme.

creating languages and solving problems

car and cdr: Implementation details in the language

define : rember a l
    cond
       : null? l
         quote ()
       : equal? (car l) a
         cdr l
       else
         cons : car l
                rember a : cdr l

define : rember a l
    cond
       : null? l
         quote ()
       : equal? (first l) a
         rest l
       else
         cons : first l
                rember a : rest l

use-modules : ice-9 match
define l '(1 2 3)
match l
    : first rest ...
      . first
; => 1

use-modules : ice-9 match
define l '(1 2 3)
match l
    : car cadr caddr 
      . cadr
; => 2
match l
    : car cdr ...
      . cdr
; => (2 3)
match '(1 (11 12) 2)
    : car (caadr cadadr) caddr ...
      . cadadr
; => 12

use-modules : ice-9 match
define l '(1 2 3)
match l 
    : fubbly dubbly duh
      . fubbly
; => 1

(use-modules (ice-9 match))
(match '(1 2 3) 
  ((car cadr caddr) 
   cadr))
   ; => 2
(match '(1 2 3) 
  ((car cadr cddr ...)
   cddr))
  ; => '(3)

Inconsistency, overhead, duplication

use-modules : oop goops ; get goops functionality
define-generic length ; allow specialization of length

define-method : length (s <string>)
    string-length s ; just reuse string-length
; that's it. Now this works:
length "123"
; => 3

use-modules : oop goops
define-generic format
define-method : format (s <string>) . rest
                apply format #f s rest

A common standard moves more slowly

Distributing and Packaging to OSX and Windows

Summary

Where Python takes you on a smooth path from Beginner to Experienced Programmer, Guile accompanies you far beyond that, after you cross over its initial bumps.

I am still a beginner of Guile Scheme myself, so I cannot show you all the ways of taking programing beyond Python with GNU Guile. That’s why I invited a few experienced Schemers as guest authors to fill the gap and give you a glimpse into the vast possibilities Guile offers for programmers.

So in addition to my own experience, the next few chapters will quote from the work of Ludovic Courtes (Ludo), Clinton (Unknown Lamer), David Thompson (davexunit), Mark Witmer and Mu Lei (NalaGinrut) to give you an idea of their experience with using Guile Scheme in fancy ways and taking programming beyond the limitations of Python.

We’ll begin with recursion and exact math, come to full posix threads and then go deep into the heart of Guile with programmable syntax, definition of completely new but interoperable languages, flexible object oriented programming and definition of control flow operators with continuations and prompts.

Recursion

define : fib n
    let rek : (i 0) (u 1) (v 1)
        if {i >= {n - 2}}
            . v
            rek {i + 1} v {u + v}

def fib(n):
    def rek(i=0, u=1, v=1):
        if i >= n-2:
            return v
        return rek(i+1, v, u+v)
    return rek()

fib 1
; => 1
fib 11
; => 89
fib 101
; => 573...[18 further numbers]
fib 1001
; => 7033...[205 further numbers]

fib(1)
# => 1
fib(11)
# => 89
fib(101)
# => 573...[18 further numbers]
fib(1001)
# => ... RuntimeError: maximum recursion depth exceeded

def fibloop(n):
   if n in (1, 2):
      return 1
   u = 1
   v = 1
   for i in range(n-2):
      tmp = v
      v = u+v
      u = tmp
   return v

define : fib n
    let rek : (i 0) (u 1) (v 1)
        if {i >= {n - 2}}
            . v
            rek {i + 1} v {u + v}

Exact Math

OverflowError: integer division result too large for a float

Real Threads!

use-modules : ice-9 futures
              srfi srfi-1 ; for better iota
define : string-append-number l
         apply string-append : map number->string l
let loop ; create a long loop. Guile is ridiculously fast 
         ; with math, so we have to make this expensive 
         ; to see an effect of concurrency.
    : i : iota 1000
    when : not : null? i
      let : : l : iota 1000 1 ; starts at 1
        let ; worst case: futures in the inner loop.
          : a : future : string-append-number l
            b : future : string-append-number : map log l
            c : future : string-append-number : map sqrt l
          ; touch gets the result of the future
          apply string-append : map touch : list a b c
      loop : cdr i

Programming the syntax and embedded domain specific languages

(define-module (gnu packages which)
  #:use-module (guix licenses)
  #:use-module (guix packages)
  #:use-module (guix download)
  #:use-module (guix build-system gnu))

(define-public which
  (package
    (name "which")
    (version "2.20")
    (source
      (origin
        (method url-fetch)
        (uri (string-append "mirror://gnu/which/which-"
                            version ".tar.gz"))
        (sha256
         (base32 (string-append
                  "1y2p50zadb36izzh2zw4dm5hvd"
                  "iydqf3qa88l8kav20dcmfbc5yl")))))
    (build-system gnu-build-system)
    (home-page "https://gnu.org/software/which/")
    (synopsis "Find full path of shell commands")
    (description (string-join
      "which is a program that prints the full paths" 
      "of executables on a system."))
    (license gpl3+)))

# Copyright 1999-2014 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
# Header: ...

EAPI="4"

inherit flag-o-matic toolchain-funcs

DESCRIPTION="Prints out location of specified executables \
that are in your path"
HOMEPAGE="https://carlowood.github.io/which/"
SRC_URI="https://carlowood.github.io/which/${P}.tar.gz"

LICENSE="GPL-3"
SLOT="0"
KEYWORDS="alpha amd64 arm arm64 hppa ia64 m68k ~mips ppc \
          ppc64 s390 sh sparc x86 ~ppc-aix ~x64-freebsd ..."
IUSE=""

src_prepare() {
        append-lfs-flags
}

src_configure() {
        tc-export AR
        default
}

...
DIST which-2.20.tar.gz 135372 SHA256 d417b... WHIRLPOOL 35ca3...
...
SIGNATURE
...

New Readers: Create languages with completely different syntax

(define-language xml-xcb
  #:title "xml-xcb"
  #:reader custom-read
  #:compilers `((scheme . ,compile-scheme))
  #:make-default-environment make-default-environment
  #:printer write)

guild compile xproto.xml --from=xml-xcb --output=xproto.go

Your own object oriented programming system

Continuations and prompts

use-modules : 2d agenda
              2d coroutine
              2d game

coroutine
  while #t
    walk 'up
    wait game-agenda 60
    walk 'down
    wait game-agenda 60

Summary

While Python is a good choice for new programmers and a great tool for solving practical problems, thanks to providing a complete set of functionality for any kind of task, encoded in a minimal set of highly polished basic concepts using very readable syntax, the structures of Python are almost stretched to their limit and extensions like list comprehensions and decorators make it more and more complicated for newcomers to really understand code from others. This makes Python yet another example for Greenspuns 10th Rule:

“Every sufficiently complex application/language/tool will either have to use Lisp or reinvent it the hard way.” — Greenspuns 10th Rule

Guile Scheme on the other hand has a higher barrier of entry and suffers from some rough edges. But when actually doing a comparison between Guile and the strongest points of Python, Guile looks quite good. It does not have the one best way to do it, which Python promotes, but that’s part of the reason why I started looking into Guile Scheme: The wish to go beyond the way of Python. Scaling a program from a first draft to a big application looks easier with Guile, and while the parentheses look odd at first, it’s extensions for infix-math and for indentation-based syntax make it a better choice for pseudocode than Python. Its standard library is much smaller than the batteries of Python, but that is partially made up for by offering an easier way to call C-libraries.

There are severe shortcomings, though. Some come from pursuing two goals at the same time: Language design and solving problems. This leads to a mix of low-level, high-level and deprecated concepts baked into the language on equal footing - as well as some baggage from compatibility to the Scheme-standard which does not allow using Guiles advanced features like easy keyword-arguments throughout. And there is no best practices guide to be found. The biggest challenge, however, is deploying a Guile-based program to platforms which do not have a decent package manager.

But these shortcomings are more than compensated by its strengths. Let-recursion (named let) is not only a testament to the elegance of recursion, but also to the reward for letting programmers define the building blocks of their language as they use them, from basic tools like elegant loop structures up to generic functions, exception handling, coroutines and boundless other possibilities. And new readers allow providing all these capabilities to new languages for specialized tasks - like parsing XML files to implement protocols directly from specifications as done in guile-xcb - while exact math has your back when other systems would fail.

Last, but not least, direct access to real threads (and consequently also truly concurrent futures) provides crucial capabilities in the current times in which even mobile phones come with multiple processors.

As a related note, learning Scheme with The Little Schemer made understanding C++ Template recursion as for example described in “Modern C++ design” (my latest reading) a breeze. So even if you don’t expect to be using Scheme to solve problems in real life, I can wholeheatedly recommend learning it to get an understanding of the possibilities programming can offer beyond Python. I expect to see more and more of its features turn up in other languages, so, if nothing else, learning Scheme will be a very worthwhile investment to prepare for the future of your favorite language.

And when it comes to Scheme, GNU Guile is a very good choice which showed that it can withstand the onslaught of time which pushed so many other languages and systems into oblivion. Guile already had many different maintainers, and it is likely that it will keep being improved in the forseeable future – similar to GNU Emacs, which is still moving forward after 30 years of development. GNUs may not always be the fastest movers, but they sure are stubborn - and that’s a very good quality to have in the core of our systems.

To sum this up there’s nothing better than the well-known quote from Victor Marie Hugo:

Nothing is as powerful as an idea whose time has come. — Victor Marie Hugo

Keep an eye on Guile Scheme: It is coming back.

Terms used by Schemers.

• Procedure: Function.
• Parens: Parentheses (round brackets)
• Thunk: One block of code. Enclosed by parens.
• Body: All the forms in a procedure.
• Form: Something which appears in a body: A definition or an expression.
• Definition: A form which starts with (define.
• Expression: Any form which can appear in the function body which is not a definition. See R4RS for the clear definition.
• RnRS: Revision n Report for Scheme
• SRFI: Scheme Request for Implementation (spelled as “surfie”). Like PEP.

File as Module and Script

if __name__ == "__main__":
    # your code
    pass

#!/bin/sh
# -*- scheme -*-
exec guile -e main -s "$0" "$@"
# Thanks to exec, the following lines 
# are never seen by the shell.
!#
(define (main args)
  (display "Hello World!"))

Output a datastructure to console to put it in the interpreter

print [1, 2, 3]

print eval("[1, 2, 3]")

(write '(1 2 3))
(newline)

(write (with-input-from-string "(1 2 3)" read))

help in interpreter

help(help)

(help help)

Profiling

import timeit
print timeit.timeit("1 + 1", number=1000000)

use-modules : statprof
with-statprof #:loop 1000000
    + 1 1

Copyright ©  2007 Free Software Foundation, Inc. http://fsf.org/

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    If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

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    The hypothetical commands show w and show c should show the appropriate parts of the General Public License. Of course, your program's commands might be different; for a GUI interface, you would use an "about box".

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It starts with a laudation for Python, the first programming language I loved.

In my first years of programming I thought that I’d never need anything else.

`Beyond Python.'

Then it dives into Guile Scheme.

Where Python takes you on a smooth path from Beginner to Experienced Programmer, Guile accompanies you far beyond after you cross over its initial bumps.

Join me on my path into Guile.

The book Apprenticeship Patterns applies the idea of patterns to personal development. It has been licensed under a Creative Commons License, though the O'Reilly page does not state that anymore. You can find the book in the chimera labs: http://chimera.labs.oreilly.com/books/1234000001813/index.html

Guile Basics collects some of the solutions I found when searching my way into GNU Guile. It is no book but rather a loose and unstructured hybrid, somewhere between a FAQ and a series of blog posts: http://draketo.de/proj/guile-basics/

Ceremony describes actions without information content which are needed only to fulfil the requirements of your tool.

This statement is a bit too general: A programming language actually is the interface between the programmer, the computer and other programmers - including the later self of the original programmer. Sometimes a bit of syntax-overhead can improve readability at the expense of convenience for the initial creation of the code. For those cases, templates can actually make sense. But this is not the case for __name__ == "__main__" and similar kludges in Python. If you want to dive into these issues, then you should start with prose or math: Text written by humans for humans, without a computer in the mix.

“The decision was made to not require parentheses in the Python language’s grammar, but as a matter of style I think you should always use them” — Description of PEP 308 in the release notes of Python 2.5. In my opinion this is a case where Python would have benefitted from requiring more parens. But then it would have shown much more clearly that the new syntax is essentially a different language style merged into Python. But still, do listen when your elected BDFL speaks. Use parens around inline if-else.

In compile time vs. runtime in Scheme Michele Simionato describes expansion, optimization and run-time, why Scheme tracks these phases and how it escaped from the dark tower of Meta-levels: http://www.phyast.pitt.edu/~micheles/scheme/scheme21.html

Aside from Guile, there are lots of other Scheme implementations. Using the posting rates to mailing lists as a rough estimate of activity, Racket (user, devel), PLT (devel, plt) and Guile (user, devel) are roughly on the same level of activity of 5 to 10 messages per day while all the other Schemes are at least factor 2 below that. So from estimating activity, Guile looks like a sane choice. But to set this into perspective: The combined posting rate of these three most active Scheme lists together only approaches the posting rate of clojure, python-devel (without counting all the other python-lists) or javascript v8 devel alone. So if you’re looking for pure activity, Scheme might not be the most obvious choice. But then, I did not find my way to Guile Scheme by searching for the most popular language. I found it while searching for ways to go beyond the limits of the languages I knew.

The opinionated guide to scheme implementations from Andy Wingo provides an overview of the wealth of Scheme implementations: http://wingolog.org/archives/2013/01/07/an-opinionated-guide-to-scheme-implementations

The Little Schemer is a popular and very readable introduction to understand the nature of computing by programming with Scheme, and a great start into thinking in recursion: https://mitpress.mit.edu/index.php?q=books/little-schemer

For some more background why I took the step to create Wisp instead of using readable, see my presentation Why Wisp?: http://draketo.de/proj/wisp/why-wisp.html

To get wisp, install Guile version 2.0.11 or later and run wget https://bitbucket.org/ArneBab/wisp/downloads/wisp-0.9.0.tar.gz; tar xf wisp-0.9.0.tar.gz ; cd wisp-0.9.0/; ./configure; make check; examples/newbase60.w 123 \\ if it prints 23, you are set up.

Hint: if you write a tutorial on Scheme, do NOT start with do-loops. Rather start with let-recursion and simple usages of SRFI-42 and foof-loop. But please don’t reference their documentation documents as if they were tutorials. That would be a very rough start.

When I realized that let-recursion provides the simplest possible model for recursive code with initialization of the recursion start, I wrote an article about my experience: http://draketo.de/licht/freie-software/let-rekursion (in german)

To get instant contact with the guile developers, visit the freenode IRC webchat: http://webchat.freenode.net?randomnick=1&channels=#guile

To get foof-loop for guile, you need to first install guildhall, a package manager for guile. See Getting Started for a short tutorial: https://github.com/ijp/guildhall/wiki/Getting-Started

In my opinion, SRFI-42 still falls a small way short of Python list comprehensions. In Python, the syntax looks like the datastructure it creates, joined in a sentence. For example, [i for i in range(5)] can be spelled as “the list containing i for each i in range up to five”. In SRFI-42 the syntax rather looks like a statement. I would spell the example (list-ec (:range i 5) i) as “the list eager comprehension which uses i from the range up to five as i”. It does not feel quite as polished as the Python version. But it is already very close and quickly becomes natural.

Sly is a game engine for Guile Scheme which provides a dynamic live coding environment that allows games to be built interactively and iteratively: http://dthompson.us/pages/software/sly.html

call-with-prompt is already the simplified version of the even more complex concept of general continuations. Let’s not go there for the time being…

The in=m example uses parenthesized syntax, because it needed a few round-trips to get right so I needed to make it as easy as possible to discuss the implementation with other Schemers.

Riastradh's Lisp Style Rules is an article which provides rules with rationales for formatting Lisp code, with some parts focussed specifically on Scheme: http://mumble.net/~campbell/scheme/style.txt

GNU Guix is a distribution built on Nix which uses GNU Guile Scheme for implementation and package definitions. It treats packages as pure functions and ensures a consistent system state even when the computer loses power during an update: http://gnu.org/s/guix

As default way I take the one which Guile uses if you give it no additional arguments: The easiest way for the programmer.

A breakable toy is a basic building block from Apprenticeship Patterns in which you choose a project which is interesting but which is not needed in production, so you can play with it without fearing to lose something if you break it. It allows easy experimentation and faster learning due to being able to try new things without having to get them perfect right away and without having to polish them for use by others: http://chimera.labs.oreilly.com/books/1234000001813/ch05.html\#breakable_toys

This example uses equal? instead of eq? to make the distinction between car/cdr and first/rest more visible. eq? compares object identity while equal? compares the content of a variable. In The Little Schemer rember uses eq? because it is defined at a point in the book where equal? is still unknown.

The Little Schemer is a popular and very readable introduction to programming with Scheme and a great start into thinking in recursion: https://mitpress.mit.edu/index.php?q=books/little-schemer

Going from cdr to cddr is similar to the way how derivation is written in mathematics: dx/dt for the first derivative, d²x/dt² for the second, and so forth. In ASCII this can be simplified to xddt - In the last 2 years I read plenty of fortran code using variable names like mdddx: The third derivative of the mass in x-direction.

Guildhall provides functionality like PyPI but is not integrated with Guile yet. It adds package management capabilities to the guild command: https://github.com/ijp/guildhall

The Adventures of a Pythonista in Schemeland is a web-based guide to Scheme for Pythonistas written and published by Michele Simionato.

The ease of using exact math in Guile impressed me so much, that I wrote an article about my experience: Exact Math to the rescue: http://draketo.de/english/exact-math-to-the-rescue

In the article ecmascript for guile Andy Wingo explains in fun and approachable style how to run (strictly written) JavaScript in Guile and access Guile features from Javascript: http://wingolog.org/archives/2009/02/22/ecmascript-for-guile

Using the ECMAscript language in Guile allows executing (clean) Javascript while retaining the full power of Scheme, including all functionality written in other Guile languages. To experiment with it, start a recent Guile (2.0.11 or newer) as guile --language=ecmascript. This enables you to do this: require("srfi.srfi-1").iota(10, 5, 7); // ftagn.

In the chapter exception handling the Guile manual explains what exceptions are and how to use exception handling in GNU Guile: http://www.gnu.org/software/guile/manual/html_node/Exceptions.html