44efc7cb48
fixed scoping of attributes (wrt declare) added 'attribute' form added internal/external literals form svn: r13574
266 lines
8.7 KiB
Racket
266 lines
8.7 KiB
Racket
#lang scribble/doc
|
|
@(require scribble/manual
|
|
scribble/struct
|
|
scribble/decode
|
|
(for-label scheme/base
|
|
scheme/contract
|
|
stxclass
|
|
stxclass/util))
|
|
|
|
@(define ellipses @scheme[...])
|
|
@(define (TODO . pre-flow)
|
|
(make-splice
|
|
(cons (bold "TODO: ")
|
|
(decode-content pre-flow))))
|
|
|
|
@title{Parsing Syntax}
|
|
@declare-exporting[stxclass]
|
|
|
|
This section describes @schememodname[stxclass]'s facilities for
|
|
parsing syntax.
|
|
|
|
@defform/subs[(syntax-parse stx-expr maybe-literals clause ...)
|
|
([maybe-literals code:blank
|
|
(code:line #:literals (literal ...))]
|
|
[literal id
|
|
(internal-id external-id)]
|
|
[clause (syntax-pattern pattern-directive ... expr)])]{
|
|
|
|
Evaluates @scheme[stx-expr], which should produce a syntax object, and
|
|
matches it against the patterns in order. If some pattern matches, its
|
|
pattern variables are bound to the corresponding subterms of the
|
|
syntax object and that clause's side conditions and @scheme[expr] is
|
|
evaluated. The result is the result of @scheme[expr].
|
|
|
|
If the syntax object fails to match any of the patterns (or all
|
|
matches fail the corresponding clauses' side conditions), a syntax
|
|
error is raised. The syntax error indicates the first specific subterm
|
|
for which no pattern matches.
|
|
|
|
A literal in the literals list has two components: the identifier used
|
|
within the pattern to signify the positions to be matched, and the
|
|
identifier expected to occur in those positions. If the
|
|
single-identifier form is used, the same identifier is used for both
|
|
purposes.
|
|
|
|
}
|
|
|
|
@defform[(syntax-parser maybe-literals clause ...)]{
|
|
|
|
Like @scheme[syntax-parse], but produces a matching procedure. The
|
|
procedure accepts a single argument, which should be a syntax object.
|
|
|
|
}
|
|
|
|
The grammar of patterns accepted by @scheme[syntax-parse] and
|
|
@scheme[syntax-parser] follows:
|
|
|
|
@schemegrammar*[#:literals (_ ...*)
|
|
[syntax-pattern
|
|
pvar-id
|
|
pvar-id:syntax-class-id
|
|
literal-id
|
|
atomic-datum
|
|
(syntax-pattern . syntax-pattern)
|
|
(syntax-pattern #,ellipses . syntax-pattern)
|
|
((head ...+) ...* . syntax-pattern)]
|
|
[pvar-id
|
|
_
|
|
id]]
|
|
|
|
Here are the variants of @scheme[syntax-pattern]:
|
|
|
|
@specsubform[pvar-id]{
|
|
|
|
Matches anything. The pattern variable is bound to the matched
|
|
subterm, unless the pattern variable is the wildcard (@scheme[_]), in
|
|
which case no binding occurs.
|
|
|
|
}
|
|
@specsubform[pvar-id:syntax-class-id]{
|
|
|
|
Matches only subterms specified by the @scheme[_syntax-class-id]. The
|
|
syntax class's attributes are computed for the subterm and bound to
|
|
the pattern variables formed by prefixing @scheme[_pvar-id.] to the
|
|
name of the attribute. @scheme[_pvar-id] is typically bound to the
|
|
matched subterm, but the syntax class can substitute a transformed
|
|
subterm instead.
|
|
|
|
@;{(for example, @scheme[expr/c] wraps the matched
|
|
subterm in a @scheme[contract] expression).}
|
|
|
|
If @scheme[_pvar-id] is @scheme[_], no pattern variables are bound.
|
|
|
|
}
|
|
@specsubform[literal-id]{
|
|
|
|
An identifier that appears in the literals list is not a pattern
|
|
variable; instead, it is a literal that matches any identifier
|
|
@scheme[free-identifier=?] to it.
|
|
|
|
Specifically, if @scheme[literal-id] is the ``internal'' name of an
|
|
entry in the literals list, then it represents a pattern that matches
|
|
only identifiers @scheme[free-identifier=?] to the ``external''
|
|
name. These identifiers are often the same.
|
|
|
|
}
|
|
@specsubform[atomic-datum]{
|
|
|
|
The empty list, numbers, strings, booleans, and keywords match as
|
|
literals.
|
|
|
|
}
|
|
@specsubform[(syntax-pattern . syntax-pattern)]{
|
|
|
|
Matches a syntax pair whose head matches the first pattern and whose
|
|
tail matches the second.
|
|
|
|
}
|
|
@;{
|
|
@specsubform[(syntax-splice-pattern . syntax-pattern)]{
|
|
|
|
Matches a syntax object which consists of any sequence of syntax
|
|
objects matching the splice pattern followed by a tail matching the
|
|
given tail pattern.
|
|
|
|
}
|
|
}
|
|
|
|
@specsubform[(syntax-pattern #,ellipses . syntax-pattern)]{
|
|
|
|
Matches a sequence of the first pattern ending in a tail matching the
|
|
second pattern.
|
|
|
|
That is, the sequence pattern matches either the second pattern (which
|
|
need not be a list) or a pair whose head matches the first pattern and
|
|
whose tail recursively matches the whole sequence pattern.
|
|
|
|
}
|
|
@specsubform/subs[#:literals (...*)
|
|
((head ...+) ...* . syntax-pattern)
|
|
([head
|
|
(code:line (syntax-pattern ...+) head-directive ...)]
|
|
[head-directive
|
|
(code:line #:min min-reps)
|
|
(code:line #:max max-reps)
|
|
(code:line #:mand)
|
|
#| (code:line #:opt)
|
|
(code:line #:occurs occurs-pvar-id)
|
|
(code:line #:default default-form)
|
|
|#])]{
|
|
|
|
Matches a sequence of any combination of the heads ending in a tail
|
|
matching the final pattern. The match is subject to constraints
|
|
specified on the heads.
|
|
|
|
@specsubform[(code:line #:min min-reps)]{
|
|
|
|
Requires at least @scheme[min-reps] occurrences of the preceding head
|
|
to match. @scheme[min-reps] must be a literal exact nonnegative
|
|
integer.
|
|
|
|
}
|
|
@specsubform[(code:line #:max max-reps)]{
|
|
|
|
Requires that no more than @scheme[max-reps] occurrences of the
|
|
preceeding head to match. @scheme[max-reps] must be a literal exact
|
|
nonnegative integer, and it must be greater than or equal to
|
|
@scheme[min-reps].
|
|
|
|
}
|
|
@specsubform[#:mand]{
|
|
|
|
Requires that the preceding head occur exactly once. Pattern variables
|
|
in the preceding head are not bound at a higher ellipsis nesting
|
|
depth.
|
|
|
|
}
|
|
@;{
|
|
@specsubform[#:opt]{
|
|
|
|
(Probably a bad idea.)
|
|
|
|
}
|
|
}
|
|
}
|
|
@;{
|
|
The variants of @scheme[_syntax-splice-pattern] follow:
|
|
|
|
@specsubform[pvar-id:syntax-splice-class-id]{
|
|
|
|
Matches a sequence of syntax objects described by
|
|
@scheme[_syntax-splice-class-id].
|
|
|
|
The name @scheme[_pvar-id] is bound, but not allowed within
|
|
expressions or @scheme[syntax] templates (since it does not refer to a
|
|
particular syntax object). Only the prefixed attributes of the splice
|
|
class are usable.
|
|
}
|
|
}
|
|
|
|
Both @scheme[syntax-parse] and @scheme[syntax-parser] support
|
|
directives for annotating the pattern and specifying side
|
|
conditions. The grammar for pattern directives follows:
|
|
|
|
@schemegrammar[pattern-directive
|
|
(code:line #:declare pattern-id syntax-class-id)
|
|
(code:line #:declare pattern-id (syntax-class-id expr ...))
|
|
(code:line #:with syntax-pattern expr)
|
|
(code:line #:when expr)]
|
|
|
|
@specsubform[(code:line #:declare pvar-id syntax-class-id)]
|
|
@specsubform[(code:line #:declare pvar-id (syntax-class-id expr ...))]{
|
|
|
|
The first form is equivalent to using the
|
|
@scheme[_pvar-id:syntax-class-id] form in the pattern (but it is
|
|
illegal to use both for a single pattern variable). The
|
|
@scheme[#:declare] form may be preferred when writing macro-defining
|
|
macros or to avoid dealing with structured identifiers.
|
|
|
|
The second form allows the use of parameterized syntax classes, which
|
|
cannot be expressed using the ``colon'' notation. The @scheme[expr]s
|
|
are evaluated outside the scope of the pattern variable bindings.
|
|
|
|
}
|
|
@specsubform[(code:line #:with syntax-pattern expr)]{
|
|
|
|
Evaluates the @scheme[expr] in the context of all previous pattern
|
|
variable bindings and matches it against the pattern. If the match
|
|
succeeds, the new pattern variables are added to the environment for
|
|
the evaluation of subsequent side conditions. If the @scheme[#:with]
|
|
match fails, the matching process backtracks. Since a syntax object
|
|
may match a pattern in several ways, backtracking may cause the same
|
|
clause to be tried multiple times before the next clause is reached.
|
|
|
|
}
|
|
@specsubform[(code:line #:when expr)]{
|
|
|
|
Evaluates the @scheme[expr] in the context of all previous pattern
|
|
variable bindings. If it produces a false value, the matching process
|
|
backtracks as described above; otherwise, it continues.
|
|
|
|
}
|
|
|
|
@defidform[...*]{
|
|
|
|
Keyword recognized by @scheme[syntax-parse] etc as notation for
|
|
generalized sequences. It may not be used as an expression.
|
|
|
|
}
|
|
|
|
@defform[(attribute attr-id)]{
|
|
|
|
Returns the value associated with the attribute named
|
|
@scheme[attr-id]. If @scheme[attr-id] is not bound as an attribute, an
|
|
error is raised. If @scheme[attr-id] is an attribute with a nonzero
|
|
ellipsis depth, then the result has the corresponding level of list
|
|
nesting.
|
|
|
|
The values returned by @scheme[attribute] never undergo additional
|
|
wrapping as syntax objects, unlike values produced by some uses of
|
|
@scheme[syntax], @scheme[quasisyntax], etc. Consequently, the
|
|
@scheme[attribute] form is preferred when the attribute value is used
|
|
as data, not placed in a syntax object.
|
|
|
|
}
|