Hi,
2013/4/29 Tomás Coiro <tomco...@hotmail.com>
> I'm trying to wrap my head around them and be able to use them.
> I'm trying to write something for a Clojure compability layer in Github
> and i just find it impossible to use the make-readtable procedure to start
> doing something.
>
>
> Can someone show me the code to make this #"hello" expand to (regexp
> "hello") ?
>
Here is one way to read #"hello" as (regexp "hello").
#lang racket
(define (read-until port ch)
(list->string
(for/list ([c (in-port read-char port)]
#:break (eqv? c ch))
c)))
;; A syntax object that has the "original?" property:
(define orig-stx (read-syntax #f (open-input-string "dummy")))
(define (lex# default-rt)
(case-lambda
[(ch port) ((lex# default-rt) ch port #f #f #f #f)]
[(ch port src line col pos)
(match (peek-char port)
[#\" (read-char port)
(define str (read-until port #\"))
(define len (+ (string-length str) 3)) ; #"" is 3 characters
(define srcloc (vector src line col pos len))
(datum->syntax #f (regexp str) srcloc orig-stx)]
[else
(read-syntax/recursive src port #\# default-rt)])]))
(define (extend-readtable rt)
(make-readtable rt #\# 'terminating-macro (lex# rt)))
(parameterize
([current-readtable (extend-readtable (current-readtable))])
(read-syntax 'foo (open-input-string "(1 2 #\"foo\" 3 4 #hash() )")))
Note that if we modify the readtable entry for # then we need
to handle all cases beginning with #. In lex# everything by #" is
handled by the old readtable.
--
Jens Axel Søgaard
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