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Raise an error when trying to iterate over an infinite trie

This commit is contained in:
Sam Caldwell 2016-02-19 15:38:43 -05:00
parent a045d54071
commit b7775efd9b
1 changed files with 21 additions and 3 deletions
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24
prospect/comprehensions.rkt
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@ -21,6 +21,16 @@
outer-stx
(list temp1 temp2 pat match-pat))))
;; trie projection symbol -> (U set exn:fail?)
;; tries to project the trie. If the resulting trie would be infinite, raise an
;; error, using the third argument to describe the pattern being projected.
;; If the resulting trie is finite, return it as a set.
(define (project-finite t proj pat)
(define s? (trie-project/set t (compile-projection (?! proj))))
(unless s?
(error "pattern projection created infinite trie:" pat))
s?)
(define-syntax (for-trie/fold stx)
(syntax-case stx ()
[(_ ([acc-id acc-init] ...)
@ -31,8 +41,7 @@
(with-syntax* ([(set-tmp loop-tmp proj-stx match-pat)
(helper #'pat_0 #'body)]
[new-acc (generate-temporary 'acc)])
#`(let ([set-tmp (trie-project/set trie_0
(compile-projection (?! proj-stx)))])
#`(let ([set-tmp (project-finite trie_0 proj-stx 'pat_0)])
(for/fold/derived #,stx ([acc-id acc-init]
...)
([loop-tmp (in-set set-tmp)])
@ -166,5 +175,14 @@
([$x (make-trie 1 2 3)])
(void)
(+ acc x))
6))
6)
;; projecting an infinite set out of an infinite trie raisies an error
(check-exn (lambda (e) (and (exn:fail? e) (not (exn:fail:contract? e))))
(lambda ()
(for-trie/list ([$x (pattern->trie 'x (projection->pattern ?))])
x)))
;; projecting something finite out is ok
(check-equal? (for-trie/list ([1 (pattern->trie 'x (projection->pattern ?))])
1)
(list 1)))