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changed apply-reduction-relation* so that it notices cycles and ignores them

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svn: r13519
This commit is contained in:
Robby Findler 2009-02-11 20:25:32 +00:00
parent 7b11c290f5
commit 3ee1a899ee
2 changed files with 19 additions and 12 deletions
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11
collects/redex/private/reduction-semantics.ss
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@ -1661,13 +1661,18 @@
(compiled-lang-nt-map lang))) (compiled-lang-nt-map lang)))
(define (apply-reduction-relation* reductions exp) (define (apply-reduction-relation* reductions exp)
(let ([answers (make-hash)]) (let ([answers (make-hash)]
[cycles (make-hash)])
(let loop ([exp exp]) (let loop ([exp exp])
(unless (hash-ref cycles exp #f)
(hash-set! cycles exp #t)
(let ([nexts (apply-reduction-relation reductions exp)]) (let ([nexts (apply-reduction-relation reductions exp)])
(cond (cond
[(null? nexts) (hash-set! answers exp #t)] [(null? nexts) (hash-set! answers exp #t)]
[else (for-each loop nexts)]))) [else (for-each loop nexts)]))))
(hash-map answers (λ (x y) x)))) (sort (hash-map answers (λ (x y) x))
string<=?
#:key (λ (x) (format "~s" x)))))
;; map/mt : (a -> b) (listof a) (listof b) -> (listof b) ;; map/mt : (a -> b) (listof a) (listof b) -> (listof b)

14
collects/redex/redex.scrbl
View File

@ -819,11 +819,12 @@ names of the reductions that were used.
[t any?]) [t any?])
(listof (listof any?))]{ (listof (listof any?))]{
apply-reduction-relation* accepts a list of reductions and a The function @scheme[apply-reduction-relation*] accepts a reduction relation and a
term. It returns the results of following every reduction term. Starting from @scheme[t], it follows every reduction
path from the term. If there are infinite reduction path and returns all of the terms that do not reduce further.
sequences starting at the term, this function will not If there are infinite reduction
terminate. sequences that do not repeat, this function will not
terminate (it does terminate if the only infinite reduction paths are cyclic).
} }
@defidform[-->]{ Recognized specially within @defidform[-->]{ Recognized specially within
@ -974,7 +975,8 @@ Tests to see if @scheme[e1] is equal to @scheme[e2].
@defform[(test--> reduction-relation e1 e2 ...)]{ @defform[(test--> reduction-relation e1 e2 ...)]{
Tests to see if the value of @scheme[e1] (which should be a term), Tests to see if the value of @scheme[e1] (which should be a term),
reduces to the @scheme[e2]s under @scheme[reduction-relation]. reduces to the @scheme[e2]s under @scheme[reduction-relation]
(using @scheme[apply-reduction-relation*], so it may not terminate).
} }
@defform[(test-predicate p? e)]{ @defform[(test-predicate p? e)]{