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+;;;; srfi-10.scm --- SRFI-10 read hash extension for Guile
+;;;;
+;;;; Copyright (C) 2001 Free Software Foundation, Inc.
+;;;;
+;;;; This program is free software; you can redistribute it and/or
+;;;; modify it under the terms of the GNU General Public License as
+;;;; published by the Free Software Foundation; either version 2, or
+;;;; (at your option) any later version.
+;;;;
+;;;; This program is distributed in the hope that it will be useful,
+;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+;;;; General Public License for more details.
+;;;;
+;;;; You should have received a copy of the GNU General Public License
+;;;; along with this software; see the file COPYING. If not, write to
+;;;; the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+;;;; Boston, MA 02111-1307 USA
+
+;;; Commentary:
+
+;;; This module implements the syntax extension #,(), also called
+;;; hash-comma, which is defined in SRFI-10.
+;;;
+;;; The support for SRFI-10 consists of the procedure
+;;; `define-reader-ctor' for defining new reader constructors and the
+;;; read syntax form
+;;;
+;;; #,(<ctor> <datum> ...)
+;;;
+;;; where <ctor> must be a symbol for which a read constructor was
+;;; defined previously.
+;;;
+;;; Example:
+;;;
+;;; (define-reader-ctor 'file open-input-file)
+;;; (define f '#,(file "/etc/passwd"))
+;;; (read-line f)
+;;; =>
+;;; :root:x:0:0:root:/root:/bin/bash"
+;;;
+;;; Please note the quote before the #,(file ...) expression. This is
+;;; necessary because ports are not self-evaluating in Guile.
+
+;;; Code:
+
+(define-module (srfi srfi-10)
+ #:use-module (ice-9 rdelim))
+
+(export define-reader-ctor)
+
+;; This hash table stores the association between comma-hash tags and
+;; the corresponding constructor procedures.
+;;
+(define reader-ctors (make-hash-table 31))
+
+;; This procedure installs the procedure @var{proc} as the constructor
+;; for the comma-hash tag @var{symbol}.
+;;
+(define (define-reader-ctor symbol proc)
+ (hashq-set! reader-ctors symbol proc)
+ (if #f #f)) ; Return unspecified value.
+
+;; Retrieve the constructor procedure for the tag @var{symbol} or
+;; throw an error if no such tag is defined.
+;;
+(define (lookup symbol)
+ (let ((p (hashq-ref reader-ctors symbol #f)))
+ (if (procedure? p)
+ p
+ (error "unknown hash-comma tag " symbol))))
+
+;; This is the actual reader extension.
+;;
+(define (hash-comma char port)
+ (let* ((obj (read port)))
+ (if (and (list? obj) (positive? (length obj)) (symbol? (car obj)))
+ (let ((p (lookup (car obj))))
+ (let ((res (apply p (cdr obj))))
+ res))
+ (error "syntax error in hash-comma expression"))))
+
+;; Install the hash extension.
+;;
+(read-hash-extend #\, hash-comma)