20 lines
627 B
Racket
20 lines
627 B
Racket
#lang racket
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(require racket/stxparam)
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(define-syntax-parameter bidi-match-going-in? #t)
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(define-syntax (define-bidi-match-expander stx)
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(syntax-case stx ()
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[(_ bidi-id in-expander out-expander)
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(syntax/loc stx
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(define-match-expander bidi-id
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(lambda (stx)
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(syntax-case stx ()
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[(_ arg (... ...) id)
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(if (syntax-parameter-value #'bidi-match-going-in?)
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(syntax/loc stx (in-expander arg (... ...) id))
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(syntax/loc stx (out-expander arg (... ...) id)))]))))]))
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(provide bidi-match-going-in?
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define-bidi-match-expander)
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