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Require a non-negative exact integer argument for `take'.

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Closes PR 11458.
This commit is contained in:
Eli Barzilay 2010-11-23 10:27:07 -05:00
parent 76c07dd594
commit f3c62a0efd
1 changed files with 10 additions and 7 deletions
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13
collects/lazy/lazy.rkt
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@ -446,7 +446,7 @@
(define* (~list-ref l k)
(let ([k (! k)])
(unless (and (integer? k) (exact? k) (<= 0 k))
(unless (exact-nonnegative-integer? k)
(raise-type-error 'list-ref "non-negative exact integer" 1 l k))
(let loop ([k k] [l (! l)])
(cond [(not (pair? l))
@ -455,7 +455,7 @@
[else (loop (sub1 k) (! (cdr l)))]))))
(define* (~list-tail l k)
(let ([k (! k)])
(unless (and (integer? k) (exact? k) (<= 0 k))
(unless (exact-nonnegative-integer? k)
(raise-type-error 'list-tail "non-negative exact integer" 1 l k))
(let loop ([k k] [l l]) ; don't force here -- unlike list-ref
(cond [(zero? k) l]
@ -575,10 +575,13 @@
;; Extra functionality that is useful for lazy list stuff
(define* (take n l)
(let loop ([n (! n)] [l (! l)])
(let ([n (! n)] [l (! l)])
(if (exact-nonnegative-integer? n)
(let loop ([n n] [l l])
(cond [(or (<= n 0) (null? l)) '()]
[(pair? l) (cons (car l) (~ (loop (sub1 n) (! (cdr l)))))]
[else (error 'take "not a proper list: ~e" l)])))
[else (error 'take "not a proper list: ~e" l)]))
(raise-type-error 'take "non-negative exact integer" 0 n l))))
;; not like Haskell's `cycle' that consumes a list
(define* (cycle . l)
@ -692,7 +695,7 @@
(define* (build-list n f)
(let ([n (! n)] [f (! f)])
(unless (and (integer? n) (exact? n) (>= n 0))
(unless (exact-nonnegative-integer? n)
(error 'build-list "~s must be an exact integer >= 0" n))
(unless (procedure? f)
(error 'build-list "~s must be a procedure" f))