42 lines
1.1 KiB
Racket
42 lines
1.1 KiB
Racket
#reader(lib "docreader.ss" "scribble")
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@require[(lib "manual.ss" "scribble")]
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@require[(lib "eval.ss" "scribble")]
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@require["guide-utils.ss"]
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@title{Named @scheme[let]}
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A named @scheme[let] is an iteration and recursion form. It uses the
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same syntactic keyword @scheme[let] as for local binding, but an
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identifier after the @scheme[let] (instead of an immediate open
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parenthesis) triggers a different parsing.
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In general,
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@schemeblock[
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(let _proc-id ([_arg-id _init-expr] ...)
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_body-expr ...+)
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]
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is equivalent to
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@schemeblock[
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(letrec ([_proc-id (lambda (_arg-id ...)
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_body-expr ...+)])
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(_proc-id _init-expr ...))
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]
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That is, a named @scheme[let] binds a procedure identifier that is
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visible only in the procedure's body, and it implicitly calls the
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procedure with the values of some initial expressions.
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@defexamples[
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(define (duplicate pos lst)
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(let dup ([i 0]
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[lst lst])
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(cond
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[(= i pos) (cons (car lst) lst)]
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[else (cons (car lst) (dup (+ i 1) (cdr lst)))])))
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(duplicate 1 (list "apple" "cheese burger!" "banana"))
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]
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