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beautiful-racket/beautiful-racket-lib/br/reader-utils.rkt

37 lines
1.7 KiB
Racket

#lang racket/base
(require (for-syntax racket/base) syntax/strip-context)
(provide define-read-and-read-syntax)
;; `define-read-functions` simplifies support for the standard reading API,
;; which asks for `read` and `read-syntax`.
;; in general, `read` is just the datum from the result of `read-syntax`.
(define-syntax (define-read-and-read-syntax calling-site-stx)
(syntax-case calling-site-stx ()
[(_ (PATH PORT) BODY ...)
(with-syntax ([READ (datum->syntax calling-site-stx 'read)]
[READ-SYNTAX (datum->syntax calling-site-stx 'read-syntax)])
#'(begin
(provide READ READ-SYNTAX)
(define (calling-site-function PATH PORT)
BODY ...) ; don't care whether this produces datum or syntax
(define (READ-SYNTAX path port)
;; because `read-syntax` must produce syntax
;; coerce a datum result to syntax if needed (à la `with-syntax`)
(define result-syntax (let ([output (calling-site-function path port)])
(if (syntax? output)
output
(datum->syntax #f output))))
;; because `read-syntax` must produce syntax without context
;; see http://docs.racket-lang.org/guide/hash-lang_reader.html
;; "a `read-syntax` function should return a syntax object with no lexical context"
(strip-context result-syntax))
(define (READ port)
; because `read` must produce a datum
(let ([output (calling-site-function #f port)])
(if (syntax? output)
(syntax->datum output)
output)))))]))