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#lang racket/base
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(require (for-syntax racket/base racket/syntax) syntax/strip-context)
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(provide define-read-and-read-syntax)
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;; `define-read-functions` simplifies support for the standard reading API,
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;; which asks for `read` and `read-syntax`.
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;; in general, `read` is just the datum from the result of `read-syntax`.
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(define-syntax (define-read-and-read-syntax calling-site-stx)
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(syntax-case calling-site-stx ()
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[(_ (PATH PORT) BODY ...)
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(let ([internal-prefix (gensym)])
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(with-syntax ([READ (datum->syntax calling-site-stx 'read)]
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[READ-SYNTAX (datum->syntax calling-site-stx 'read-syntax)]
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;; use prefixed names to prevent namespace collisions with possibly existing `read` & `read-syntax`
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[INTERNAL-READ (format-id #'here "~a-~a" internal-prefix 'read)]
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[INTERNAL-READ-SYNTAX (format-id #'here "~a-~a" internal-prefix 'read-syntax)])
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#'(begin
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(provide (rename-out [INTERNAL-READ READ]
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[INTERNAL-READ-SYNTAX READ-SYNTAX]))
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(define (calling-site-function PATH PORT)
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BODY ...) ; don't care whether this produces datum or syntax
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(define INTERNAL-READ-SYNTAX
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(procedure-rename (λ (path port) ; rename proc so it looks right in the REPL (otherwise retains internal prefix name)
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;; because `read-syntax` must produce syntax
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;; coerce a datum result to syntax if needed (à la `with-syntax`)
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(define result-syntax (let ([output (calling-site-function path port)])
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(if (syntax? output)
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output
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(datum->syntax #f output))))
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;; because `read-syntax` must produce syntax without context
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;; see http://docs.racket-lang.org/guide/hash-lang_reader.html
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;; "a `read-syntax` function should return a syntax object with no lexical context"
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(strip-context result-syntax)) 'READ-SYNTAX))
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(define INTERNAL-READ
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(procedure-rename (λ (port)
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; because `read` must produce a datum
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(let ([output (calling-site-function #f port)])
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(if (syntax? output)
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(syntax->datum output)
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output))) 'READ)))))]))
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