CHICKEN for Python programmers
  1. CHICKEN for Python programmers
  2. Hello, world!
    1. Python
    2. CHICKEN
  3. Definitions, assignment and bindings
    1. Python
    2. CHICKEN
  4. Strings
    1. Concatenating
      1. Python
      2. CHICKEN
    2. Splitting a string
      1. Python
      2. CHICKEN
  5. File I/O
    1. Reading the contents of a file and returning a string
      1. Python
      2. CHICKEN
    2. Reading the contents of a file and returning a list of lines
      1. Python
      2. CHICKEN
  6. Conditionals
    1. Single condition
      1. Python
      2. CHICKEN
    2. Multiple conditions
      1. Python
      2. CHICKEN
  7. Iteration
    1. Iterating through and printing the elements of a list
      1. Python
      2. CHICKEN
    2. Applying a procedure/function to each item of a list
      1. Python
      2. CHICKEN
  8. Other references

Hello, world!

Python

 
print "Hello, world!"

CHICKEN

 
(print "Hello, world!")

Definitions, assignment and bindings

Python

Python has only one operator for both assignments and definitions of variables (=).

a = 0

CHICKEN

Defining a variable:

(define a 0)

Assigning a variable a value:

(set! a 0)

PS: CHICKEN automatically defines a global variable when a variable is set without being defined. However, it is best practice (and most compatible with other Schemes) to define all variables.

Binding a value to a variable:

(let ((a 0))
   a)

Strings

Concatenating

Python

 
a = "1" + "2"
a = "".join(["1", "2"])
a = sum(["1", "2"], start="")

CHICKEN

 
(string-append "1" "2")
(import (chicken string))
(conc "1" "2")
(import (chicken string)) ;; If you hadn't already
(string-intersperse '("1" "2") "")

Splitting a string

Python

 
"this is a string".split()

CHICKEN

 
(import (chicken string)) ;; If you hadn't already
(string-split "this is a string")

File I/O

Reading the contents of a file and returning a string

Python

 
open("my-file.txt").read() # Deprecated
with open("my-file.txt") as f:
    f.read()

CHICKEN

 
(import (chicken io))

(call-with-input-file "my-file.txt" (lambda (port) (read-string #f port)))

read-string is defined in the (chicken io) module. This module is not loaded by default, so we import it first.

call-with-input-file calls its argument procedure with the opened file as an argument. The first argument to read-string is the limit, which tells it how many characters to read. We use #f to indicate we want to read everything (no limit).

Reading the contents of a file and returning a list of lines

Python

 
open("my-file.txt").readlines()
with open("my-file.txt") as f:
    f.readlines()

CHICKEN

 
(import (chicken io))

(call-with-input-file "my-file.txt" (lambda (port) (read-lines port)))

read-lines is also defined in the (chicken io) module.

Conditionals

Single condition

Python

 
"yes" if 1<2 else "no"

CHICKEN

 
(if (< 1 2) "yes" "no")

PS: in Scheme, the result of the evaluation of an if form returns the value of the arm that was taken, just as in the shorthand if form of Python. You can see this by the fact that the interpreter prints back the string, which is the value of the entire expression.

Multiple conditions

Python

 
result = None
if 1 < 2:
    result = "1 < 2"
elif 1 > 2:
    result = "1 > 2"
else:
    result = "1 = 2"

CHICKEN

 
(cond ((< 1 2) "1 < 2")
      ((> 1 2) "1 > 2")
      (else "1 = 2"))

PS: in Scheme, the result of the evaluation of a cond form is also the value of the expression in the arm that was taken.

Iteration

Iterating through and printing the elements of a list

Python

 
l = [1, 2, 3, 4]
for i in l:
    print i

CHICKEN

 
(define l '(1 2 3 4))
(for-each print l)

Applying a procedure/function to each item of a list

Python

 
l = [1, 2, 3, 4]

def add10(n):
    return n + 10

[ add10(i) for i in l ]

CHICKEN

 
(define l '(1 2 3 4))

(define (add10 n) (+ n 10))

(map add10 l)

Other references

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