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Improved docs and error messages for define-metafunction/extension

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svn: r17635
This commit is contained in:
Casey Klein 2010-01-13 18:21:27 +00:00
parent e4fdd172a7
commit a47d38e15d
2 changed files with 42 additions and 21 deletions
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7
collects/redex/private/reduction-semantics.ss
View File

@ -1077,6 +1077,11 @@
(raise-syntax-error syn-error-name "expected an identifier in the language position" orig-stx #'lang))
(when (null? (syntax-e #'rest))
(raise-syntax-error syn-error-name "no clauses" orig-stx))
(when prev-metafunction
(syntax-local-value
prev-metafunction
(λ ()
(raise-syntax-error syn-error-name "expected a previously defined metafunction" orig-stx prev-metafunction))))
(prune-syntax
(let ([lang-nts (language-id-nts #'lang 'define-metafunction)]) ;; keep this near the beginning, so it signals the first error (PR 10062)
(let-values ([(contract-name dom-ctcs codom-contract pats)
@ -1114,6 +1119,8 @@
(list name
(car names)))))
(loop name (cdr names))]))])
(when (and prev-metafunction (eq? (syntax-e #'name) (syntax-e prev-metafunction)))
(raise-syntax-error syn-error-name "the extended and extending metafunctions cannot share a name" orig-stx prev-metafunction))
(parse-extras #'((stuff ...) ...))
(with-syntax ([(((cp-let-bindings ...) rhs/wheres) ...)
(map (λ (sc/b rhs)

56
collects/redex/redex.scrbl
View File

@ -628,18 +628,17 @@ extended non-terminals. For example, this language:
@schemeblock[
(define-extended-language lc-num-lang
lc-lang
(e .... (code:comment "extend the previous `e' non-terminal")
+
number)
(v ....
(v .... (code:comment "extend the previous `v' non-terminal")
+
number)
(x (variable-except lambda +)))
]
extends lc-lang with two new alternatives for both the @scheme[e]
and @scheme[v] nonterminal, replaces the @scheme[x] non-terminal with a
new one, and carries the @scheme[c] non-terminal forward.
extends lc-lang with two new alternatives for the @scheme[v]
non-terminal, carries forward the @scheme[e] and @scheme[c]
non-terminals, and replaces the @scheme[x] non-terminal with a
new one (which happens to be equivalent to the one that would
have been inherited).
The four-period ellipses indicates that the new language's
non-terminal has all of the alternatives from the original
@ -886,16 +885,16 @@ all non-GUI portions of Redex) and also exported by
@schememodname[redex] (which includes all of Redex).
@defform/subs[#:literals (: ->)
(define-metafunction language-exp
(define-metafunction language
contract
[(name @#,ttpattern ...) @#,tttterm extras ...]
...)
([contract (code:line)
(code:line id : @#,ttpattern ... -> @#,ttpattern)]
[extras (side-condition scheme-expression)
(where tl-pat @#,tttterm)]
[tl-pat identifier (tl-pat-ele ...)]
[tl-pat-ele tl-pat (code:line tl-pat ... (code:comment "a literal ellipsis"))])]{
([contract (code:line)
(code:line id : @#,ttpattern ... -> @#,ttpattern)]
[extras (side-condition scheme-expression)
(where tl-pat @#,tttterm)]
[tl-pat identifier (tl-pat-ele ...)]
[tl-pat-ele tl-pat (code:line tl-pat ... (code:comment "a literal ellipsis"))])]{
The @scheme[define-metafunction] form builds a function on
sexpressions according to the pattern and right-hand-side
@ -969,17 +968,32 @@ match.
}
@defform[(define-metafunction/extension extending-name language-exp
@defform[(define-metafunction/extension f language
contract
[(name @#,ttpattern ...) @#,tttterm (side-condition scheme-expression) ...]
[(g @#,ttpattern ...) @#,tttterm extras ...]
...)]{
This defines a metafunction as an extension of an existing
one. The extended metafunction behaves as if the original
patterns were in this definitions, with the name of the
function fixed up to be @scheme[extending-name].
Defines a metafunction @scheme[g] as an extension of an existing
metafunction @scheme[f]. The metafunction @scheme[g] behaves as
if @scheme[f]'s clauses were appended to its definition (with the
function position of the left-hand sides changed to from @scheme[f]
to @scheme[g]).
}
For example, @scheme[define-metafunction/extension] may be used to extend
the free-vars function above to the forms introduced by the language
lc-num-lang.
@schemeblock[
(define-metafunction/extension free-vars lc-num-lang
free-vars-num : e -> (x ...)
[(free-vars-num number)
()]
[(free-vars-num (+ e_1 e_2))
(∪ (free-vars-num e_1)
(free-vars-num e_2))])
]
@defform[(in-domain? (metafunction-name @#,tttterm ...))]{
Returns @scheme[#t] if the inputs specified to @scheme[metafunction-name] are
legtimate inputs according to @scheme[metafunction-name]'s contract,
@ -987,7 +1001,7 @@ and @scheme[#f] otherwise.
}
@defform/subs[#:literals ()
(define-relation language-exp
(define-relation language
[(name @#,ttpattern ...) @#,tttterm ...] ...)
([tl-pat identifier (tl-pat-ele ...)]
[tl-pat-ele tl-pat (code:line tl-pat ... (code:comment "a literal ellipsis"))])]{