42 lines
1.5 KiB
Racket
42 lines
1.5 KiB
Racket
#lang scribble/doc
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@(require "common.rkt" (for-label syntax/free-vars) scribble/example)
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@title[#:tag "free-vars"]{Computing the Free Variables of an Expression}
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@defmodule[syntax/free-vars]
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@defproc[(free-vars [expr-stx syntax?]
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[insp inspector? _mod-decl-insp]
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[#:module-bound? module-bound? any/c #f])
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(listof identifier?)]{
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Returns a list of free @racket[lambda]- and @racket[let]-bound
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identifiers in @racket[expr-stx] in the order in which each
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identifier first appears within @racket[expr-stx]. The expression must be fully
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expanded (see @secref[#:doc refman "fully-expanded"] and
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@racket[expand]).
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The inspector @racket[insp] is used to disarm @racket[expr-stx] and
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sub-expressions before extracting identifiers. The default
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@racket[insp] is the declaration-time inspector of the
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@racketmodname[syntax/free-vars] module.}
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If @racket[module-bound?] is non-false, the list of free variables also
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includes free module-bound identifiers.
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@examples[
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(require (for-syntax racket/base syntax/parse syntax/free-vars))
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(define-syntax (print-body-free-vars stx)
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(syntax-parse stx
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#:literals (lambda)
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[(_ (~and lam (lambda (a ...) b ...)))
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(define expanded-body (local-expand #'lam 'expression '()))
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(syntax-parse expanded-body
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#:literals (#%plain-lambda)
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[(#%plain-lambda (arg ...) body)
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(displayln (free-vars #'body))
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expanded-body])]))
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(lambda (x) (print-body-free-vars (lambda (y) x)))
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]
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