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1.2 KiB
1.2 KiB
Named let
A named let is an iteration and recursion form. It uses the same
syntactic keyword let as for local binding, but an identifier after
the let instead of an immediate open parenthesis triggers a
different parsing.
(let proc-id ([arg-id init-expr] ...)
body ...+)
A named let form is equivalent to
(letrec ([proc-id (lambda (arg-id ...)
body ...+)])
(proc-id init-expr ...))
That is, a named 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.
Examples:
(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"))
'("apple" "cheese burger!" "cheese burger!" "banana")