GNU Guile

Implementation of programming language Lisp

GNU Guile (Guile stands for Gnu’s Ubiquitous Interactive Language for Extension) is an interpreter/virtual machine for Lisp which implements Scheme dialect. It was first released in 1993.

GNU Guile was developed to become a scripting language to replace Tcl.

Guile includes modularized extensions for POSIX system calls, APL array functionality, and others, packaged as an object library. “Libguile” allows Guile to be embedded in other programs and used as an interface for other languages.

GNU Guile logo
GNU Guile logo

Links:

Examples:

Hello, World!:

Example for versions JScheme 7.2, MIT/GNU Scheme 7.7.9, guile 1.8.5

Printing a message is a side effect of this command. Depending on the chosen implementation, the command will return either the message printed, or Unspecified return value. 

(write "Hello, World!")

Factorial:

Example for versions JScheme 7.2, MIT/GNU Scheme 7.7.9, guile 1.8.5

This example uses tail-recursive factorial calculation. Note that GNU Guile and MIT/GNU Scheme print correct result, while JScheme has values of factorial starting with 13! wrong due to overflow. 

(define (factorial x)
  (if (< x 2)
    1
    (* x (factorial (- x 1)))))

(do ((i 0 (+ i 1)))
  ((> i 16))
    (display (string-append (number->string i) "! = "))
    (display (number->string (factorial i)))
    (newline))

Fibonacci numbers:

Example for versions JScheme 7.2, MIT/GNU Scheme 7.7.9, guile 1.8.5

This example uses recursive definition of Fibonacci numbers. 

(define (fibonacci x)
  (if (< x 2)
    x
    (+ (fibonacci (- x 1)) (fibonacci (- x 2)))))

(do ((i 1 (+ i 1)))
  ((> i 16))
    (display (string-append (number->string (fibonacci i)) ", ")))
(display "...")
(newline)

Quadratic equation:

Example for versions guile 1.8.5

begin is used to execute several commands in row. 

(define A (read))
(define B (read))
(define C (read))
(define D (- (* B B) (* 4 A C)))
(if (= A 0)
  (display "Not a quadratic equation.")
  (begin
   (define k1 (/ B -2 A))
   (define k2 (/ (sqrt (abs D)) 2 A))
   (if (= D 0)
    (begin (display "x = ") (display k1))
    (if (> D 0)
      (begin (display "x1 = ") (display (+ k1 k2)) (newline) (display "x2 = ") (display (- k1 k2)))
      (begin (display "x1 = (") (display k1) (display ", ") (display k2) (display ")") (newline)
             (display "x2 = (") (display k1) (display ", ") (display (- k2)) (display ")"))))))

CamelCase:

Example for versions guile 1.8.5

This program shows how to use regular expressions from regex module. First two commands load the necessary modules. The third one reads a line from input stream using read-line command (rdelim module) — unlike plain read, it consumes characters till the end of line, not till the first whitespace — and converts it to lowercase.

The fourth command finds all matches for a regexp which describes a sequence of lowercase letters. Then it replaces each match with a return of a certain function applied to it (bound using lambda). In this case the function is string-titlecase which converts the first character of the string to uppercase.

Finally, the fifth command removes all non-letter characters from the string. 

(use-modules (ice-9 regex))
(use-modules (ice-9 rdelim))
(define text (string-downcase (read-line)))
(define text (regexp-substitute/global #f "[a-z]+"  text 'pre (lambda (m) (string-titlecase (match:substring m))) 'post))
(define text (regexp-substitute/global #f "[^a-zA-Z]+"  text 'pre 'post))
(display text)