d7a87c79e0
Changed backtracking algorithm, runtime representations
- syntax classes, ~describe no longer implicitly commit
- ~describe no longer delimits effect of cut
Added keyword & optional args for stxclasses
Added ~do and #:do, ~post, ~commit and #:commit,
~delimit-cut and #:no-delimit-cut
Added syntax/parse/debug, syntax/parse/experimental/*
- expr/c for contracting macro sub-expressions
moved from syntax/parse to syntax/parse/experimental/contract
- syntax class reflection (~reflect, ~splicing-reflect)
- eh-alternative-sets (~eh-var)
- provide-syntax-class/contract
(only for params, not attrs so far)
Changed ~fail to not include POST progress (#:fail still does)
old (~fail _) is now (~post (~fail _))
Made msg argument of ~fail optional
Removed generic "repetition constraint violated" msg
Removed atom-in-list stxclass
Removed unnecessary datum->syntax on cdr of pair pattern
massive improvements to long-list microbenchmarks
Optimization: integrable syntax classes (id, expr, keyword)
need better measurements
Optimization: ad hoc elimination of head/tail choice point
for (EH ... . ()) patterns
Added unstable/wrapc (proc version of expr/c)
43 lines
1.5 KiB
Racket
43 lines
1.5 KiB
Racket
#lang scribble/doc
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@(require scribble/manual
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scribble/struct
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scribble/decode
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scribble/eval
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"parse-common.rkt"
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(for-label racket/class))
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@title[#:tag "exprc"]{Experimental: Contracts on macro sub-expressions}
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@emph{This section involves facilities that are experimental and
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subject to change.}
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Just as procedures often expect certain kinds of values as arguments,
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macros often have expectations about the expressions they are
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given. And just as procedures express those expectations via
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contracts, so can macros, using the @scheme[expr/c] syntax class.
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For example, here is a macro @scheme[myparameterize] that behaves like
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@scheme[parameterize] but enforces the @scheme[parameter?] contract on
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the parameter expressions.
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@myinteraction[
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(define-syntax (myparameterize stx)
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(syntax-parse stx
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[(_ ((p v:expr) ...) body:expr)
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#:declare p (expr/c #'parameter?
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#:name "parameter argument")
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#'(parameterize ((p.c v) ...) body)]))
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(myparameterize ((current-input-port
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(open-input-string "(1 2 3)")))
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(read))
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(myparameterize (('whoops 'something))
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'whatever)
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]
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@bold{Important:} Make sure when using @scheme[expr/c] to use the
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@scheme[c] attribute. If the macro above had used @scheme[p] in the
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template, the expansion would have used the raw, unchecked
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expressions. The @scheme[expr/c] syntax class does not change how
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pattern variables are bound; it only computes an attribute that
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represents the checked expression.
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