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documented :stxclass patterns

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closes PR 13565
This commit is contained in:
Ryan Culpepper 2013-02-27 15:39:59 -05:00
parent b40c91e6f4
commit 616ca51f75
1 changed files with 10 additions and 3 deletions
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13
collects/syntax/scribblings/parse/patterns.scrbl
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@ -218,7 +218,7 @@ An identifier can be either a @tech{pattern variable}, an
@item{If @racket[id] is of the form @racket[_pvar-id:syntax-class-id] @item{If @racket[id] is of the form @racket[_pvar-id:syntax-class-id]
(that is, two names joined by a colon character), it is an (that is, two names joined by a colon character), it is an
@tech{annotated pattern variable}, and the pattern is equivalent to @tech{annotated pattern variable}, and the pattern is equivalent to
@racket[(~var pvar-id syntax-class-id)]. @racket[(~var _pvar-id _syntax-class-id)].
@myexamples[ @myexamples[
(syntax-parse #'a (syntax-parse #'a
@ -235,6 +235,10 @@ An identifier can be either a @tech{pattern variable}, an
#:declare t two #:declare t two
(syntax->datum #'(t t.x t.y))]) (syntax->datum #'(t t.x t.y))])
] ]
Note that an @racket[id] of the form @racket[_:syntax-class-id] is
legal; see the discussion of a @ref[~var s+] form with a zero-length
@svar[pvar-id].
} }
@item{Otherwise, @racket[id] is a @tech{pattern variable}, and the @item{Otherwise, @racket[id] is a @tech{pattern variable}, and the
@ -265,7 +269,7 @@ class inserted.
An @deftech{annotated pattern variable}. The pattern matches only An @deftech{annotated pattern variable}. The pattern matches only
terms accepted by @svar[syntax-class-id] (parameterized by the terms accepted by @svar[syntax-class-id] (parameterized by the
@racket[arg-expr]s, if present). @racket[arg]s, if present).
In addition to binding @svar[pvar-id], an annotated pattern In addition to binding @svar[pvar-id], an annotated pattern
variable also binds @deftech{nested attributes} from the syntax variable also binds @deftech{nested attributes} from the syntax
@ -273,7 +277,10 @@ class. The names of the nested attributes are formed by prefixing
@svar[pvar-id.] (that is, @svar[pvar-id] followed by a ``dot'' @svar[pvar-id.] (that is, @svar[pvar-id] followed by a ``dot''
character) to the name of the syntax class's attribute. character) to the name of the syntax class's attribute.
If @svar[pvar-id] is @racket[_], no attributes are bound. If @svar[pvar-id] is @racket[_], no attributes are bound. If
@svar[pvar-id] is the zero-length identifier (@racket[||]), then
@svar[pvar-id] is not bound, but the nested attributes of
@racket[syntax-class-use] are bound without prefixes.
If @racket[role-expr] is given and evaluates to a string, it is If @racket[role-expr] is given and evaluates to a string, it is
combined with the syntax class's description in error messages. combined with the syntax class's description in error messages.