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syntax-case docs: clarify grammar of "rest" patterns

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The grammar constraint was specified in prose, but but in a way that
clearly covered both cases, and adjusting the grammar seems clearer.
This commit is contained in:
Matthew Flatt 2018-06-01 17:47:02 +08:00
parent 8d56c29317
commit 0ab9de2fb1
1 changed files with 21 additions and 25 deletions
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46
pkgs/racket-doc/scribblings/reference/stx-patterns.scrbl
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@ -11,23 +11,24 @@
@title[#:tag "stx-patterns"]{Pattern-Based Syntax Matching}
@defform/subs[(syntax-case stx-expr (literal-id ...)
@defform/subs[#:literals (_)
(syntax-case stx-expr (literal-id ...)
clause ...)
([clause [pattern result-expr]
[pattern fender-expr result-expr]]
[pattern _
id
[pattern np-pattern
(pattern ...)
(pattern ...+ . pattern)
(pattern ... pattern ellipsis pattern ...)
(pattern ... pattern ellipsis pattern ... . pattern)
(code:line #,(tt "#")(pattern ...))
(code:line #,(tt "#")(pattern ... pattern ellipsis pattern ...))
(code:line #,(tt "#&")pattern)
(code:line #,(tt "#s")(key-datum pattern ...))
(code:line #,(tt "#s")(key-datum pattern ... pattern ellipsis pattern ...))
(ellipsis stat-pattern)
const]
(pattern ...+ . np-pattern)
(pattern ... pattern ellipsis pattern ... . np-pattern)]
[np-pattern _
id
(code:line #,(tt "#")(pattern ...))
(code:line #,(tt "#")(pattern ... pattern ellipsis pattern ...))
(code:line #,(tt "#&")pattern)
(code:line #,(tt "#s")(key-datum pattern ...))
(code:line #,(tt "#s")(key-datum pattern ... pattern ellipsis pattern ...))
(ellipsis stat-pattern)
const]
[stat-pattern id
(stat-pattern ...)
(stat-pattern ...+ . stat-pattern)
@ -79,18 +80,13 @@ A syntax object matches a @racket[pattern] as follows:
Any @tech{pattern variables} bound by the sub-@racket[pattern]s are
bound by the complete pattern; the bindings must all be distinct.}
@specsubform[(pattern ...+ . pattern)]{
The last @racket[pattern] must not be a @racket/form[(pattern ...)],
@racket/form[(pattern ...+ . pattern)], @racket/form[(pattern ... pattern
ellipsis pattern ...)], or @racket/form[(pattern ... pattern ellipsis
pattern ... . pattern)] form.
@specsubform[(pattern ...+ . np-pattern)]{
Like the previous kind of pattern, but matches syntax objects that
are not necessarily lists; for @math{n} sub-@racket[pattern]s before
the last sub-@racket[pattern], the syntax object's datum must be a
pair such that @math{n-1} @racket[cdr]s produce pairs. The last
sub-@racket[pattern] is matched against the syntax object
the final @racket[np-pattern], the syntax object's datum must be a
pair such that @math{n-1} @racket[cdr]s produce pairs. The final
@racket[np-pattern] is matched against the syntax object
corresponding to the @math{n}th @racket[cdr] (or the
@racket[datum->syntax] coercion of the datum using the nearest
enclosing syntax object's lexical context and source location).}
@ -111,11 +107,11 @@ A syntax object matches a @racket[pattern] as follows:
lists of syntax objects with a @tech{depth marker} of @math{2}, and
so on.)}
@specsubform[(pattern ... pattern ellipsis pattern ... . pattern)]{
@specsubform[(pattern ... pattern ellipsis pattern ... . np-pattern)]{
Like the previous kind of pattern, but with a final
sub-@racket[pattern] as for @racket[(pattern ...+ . pattern)]. The
final @racket[pattern] never matches a syntax object whose datum is a
@racket[np-pattern] as for @racket[(pattern ...+ . np-pattern)]. The
final @racket[np-pattern] never matches a syntax object whose datum is a
pair.}
@specsubform[(code:line #,(tt "#")(pattern ...))]{