ac26fe7554
Also, updates some of the mzlib files to point at `racket/*' libraries rather than to `scheme/*' ones.
38 lines
1012 B
Racket
38 lines
1012 B
Racket
#lang scribble/doc
|
|
@(require scribble/manual scribble/eval "guide-utils.rkt")
|
|
|
|
@title{Named @racket[let]}
|
|
|
|
A named @racket[let] is an iteration and recursion form. It uses the
|
|
same syntactic keyword @racket[let] as for local binding, but an
|
|
identifier after the @racket[let] (instead of an immediate open
|
|
parenthesis) triggers a different parsing.
|
|
|
|
@specform[
|
|
(let _proc-id ([_arg-id _init-expr] ...)
|
|
_body ...+)
|
|
]
|
|
|
|
A named @racket[let] form is equivalent to
|
|
|
|
@racketblock[
|
|
(letrec ([_proc-id (lambda (_arg-id ...)
|
|
_body ...+)])
|
|
(_proc-id _init-expr ...))
|
|
]
|
|
|
|
That is, a named @racket[let] binds a function identifier that is
|
|
visible only in the function's body, and it implicitly calls the
|
|
function with the values of some initial expressions.
|
|
|
|
@defexamples[
|
|
(define (duplicate pos lst)
|
|
(let dup ([i 0]
|
|
[lst lst])
|
|
(cond
|
|
[(= i pos) (cons (car lst) lst)]
|
|
[else (cons (car lst) (dup (+ i 1) (cdr lst)))])))
|
|
(duplicate 1 (list "apple" "cheese burger!" "banana"))
|
|
]
|
|
|