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try to explain enumerator mismatch bug more carefully

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Robby Findler 2014-02-10 09:30:18 -06:00
parent ca3757367d
commit 418f1d015d
1 changed files with 13 additions and 9 deletions
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22
pkgs/redex-pkgs/redex-doc/redex/scribblings/ref.scrbl
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@ -1830,9 +1830,9 @@ Generates terms in a number of different ways:
The @racket[string] enumeration produces all single character strings before
going on to strings with multiple characters. For each character it starts
the lowercase Latin characters, then upercase Latin, and then every remaining Unicode
character. The @racket[variable] enumeration is the same, except it produces
symbols instead of strings.
the lowercase Latin characters, then uppercase Latin, and then every remaining
Unicode character. The @racket[variable] enumeration is the same, except it
produces symbols instead of strings.
@examples[#:eval
redex-eval
@ -1863,7 +1863,7 @@ Generates terms in a number of different ways:
(for/list ([i (in-range 10)])
(generate-term L unused #:i-th i))]
Finally, the @racket[any] pattern enumerates sexpressions of the above base-types.
Finally, the @racket[any] pattern enumerates sexpressions of the above base types.
@examples[#:eval
redex-eval
(for/list ([i (in-range 20)])
@ -1900,15 +1900,19 @@ Generates terms in a number of different ways:
(generate-term L overlap #:i-th i))]
For similar reasons, enumerations for mismatch
patterns @racket[_!_] are unsound in the presence of
ambiguity, but work as expected for unambiguous
grammars.
patterns @racketvarfont[_!_] do not work properly when given ambiguous patterns;
they may repeat elements of the enumeration.
@examples[#:eval
redex-eval
(define-language Bad
(ambig ::= (x ... x ...)))
(generate-term Bad (ambig_!_1 ambig_!_1 #:i-th 4))]
(generate-term Bad (ambig_!_1 ambig_!_1) #:i-th 4)]
In this case, the elements of the resulting list are the same,
even though they should not be, according to the pattern. Internally,
the enumerator has discovered two different ways to generate @racket[ambig]
(one where the @racket[x] comes from the first ellipses and one from the second)
but those two different ways produce the same term and so the enumerator
incorrectly produces @racket[(x x)].
}
@item{@racket[from-judgment-form]: Randomly picks a term that satisfies