Zen

Translation

(list 2 a 5 7append (list 1 2) (list 3 4))
@result{} (1 2 3 5 74)
English type: lisp
(append (list 1 2) (list 3 4))
@result{} (1 2 3 4)

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(display (string-append "Hello " "Guix" "\n"))
@print{} Hello Guix!
@result{} #<unspecified>
 
This last example is a function call nested in another function call. When a parenthesized expression is evaluated, the first term is the function and the rest are the arguments passed to the function. Every function returns the last evaluated expression as its return value.
 
Anonymous functions---@dfn{procedures} in Scheme parlance---are declared with the @code{lambda} term:
 
(lambda (x) (* x x))
@result{} #<procedure 120e348 at <unknown port>:24:0 (x)>
 
The above procedure returns the square of its argument. Since everything is an expression, the @code{lambda} expression returns an anonymous procedure, which can in turn be applied to an argument:
 
((lambda (x) (* x x)) 3)
@result{} 9
((lambda (x) (* x x)) 3)
@result{} 9
Procedures are regular values just like numbers, strings, Booleans, and so on.
 
Anything can be assigned a global name with @code{define}:
 
(define a 3)
(define square (lambda (x) (* x x)))
(square a)
@result{} 9
(define a 3)
(define square (lambda (x) (* x x)))
(square a)
@result{} 9
Procedures can be defined more concisely with the following syntax:
 
(define (square x) (* x x))
(define (square x) (* x x))
A list structure can be created with the @code{list} procedure:
 
(list 2 a 5 7)
@result{} (2 3 5 7)
(list 2 a 5 7)
@result{} (2 3 5 7)
Standard procedures are provided by the @code{(srfi srfi-1)} module to create and process lists (@pxref{SRFI-1, list processing,, guile, GNU Guile Reference Manual}). Here are some of the most useful ones in action:
 
(use-modules (srfi srfi-1)) ;import list processing procedures

 
(append (list 1 2) (list 3 4))
@result{} (1 2 3 4)

(list 2 a 5 7)
@result{} (2 3 5 7)
(map (lambda (x) (* x x)) (list 1 2 3 4))
@result{} (1 4 9 16)

((lambda (x) (* x x)) 3)
@result{} 9
(delete 3 (list 1 2 3 4)) @result{} (1 2 4)
(filter odd? (list 1 2 3 4)) @result{} (1 3)
(remove even? (list 1 2 3 4)) @result{} (1 3)
(find number? (list "a" 42 "b")) @result{} 42
 
Notice how the first argument to @code{map}, @code{filter}, @code{remove}, and @code{find} is a procedure!
 
S-expression
 
The @dfn{quote} disables evaluation of a parenthesized expression, also called an S-expression or ``s-exp'': the first term is not called over the other terms (@pxref{Expression Syntax, quote,, guile, GNU Guile Reference Manual}). Thus it effectively returns a list of terms.
 
'(display (string-append "Hello " "Guix" "\n"))
@result{} (display (string-append "Hello " "Guix" "\n"))

 
'(2 a 5 7)
@result{} (2 a 5 7)
'(2 a 5 7)
@result{} (2 a 5 7)
The @code{quasiquote} (@code{`}, a backquote) disables evaluation of a parenthesized expression until @code{unquote} (@code{,}, a comma) re-enables it. Thus it provides us with fine-grained control over what is evaluated and what is not.
 
`(2 a 5 7 (2 ,a 5 ,(+ a 4)))
@result{} (2 a 5 7 (2 3 5 7))
`(2 a 5 7 (2 ,a 5 ,(+ a 4)))
@result{} (2 a 5 7 (2 3 5 7))
Note that the above result is a list of mixed elements: numbers, symbols (here @code{a}) and the last element is a list itself.
 
G-expressions, syntax
 
gexps, syntax
 
#~
 
#$
 
gexp
 

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String updated in the repository
(append (list 1 2) (list 3 4))
@result{} (1 2 3 4)

(list 2 a 5 7)
@result{} (2 3 5 7)
a year ago
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Source string changed
(list 2 a 5 7append (list 1 2) (list 3 4))
@result{} (1 2 3 5 74)
a year ago
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14917449 String information

Source string description
type: lisp
Flags
ignore-same, no-wrap
Source string location
guix-git/doc/guix-cookbook.texi:337
String age
a year ago
Last updated
4 weeks ago
Source string age
a year ago
Translation file
po/doc/guix-cookbook.uk.po, string 158