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Diffstat (limited to 'srfi/srfi-10.scm')
-rw-r--r-- | srfi/srfi-10.scm | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/srfi/srfi-10.scm b/srfi/srfi-10.scm new file mode 100644 index 000000000..0ce743af3 --- /dev/null +++ b/srfi/srfi-10.scm @@ -0,0 +1,85 @@ +;;;; 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) |