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Diffstat (limited to 'module/srfi/srfi-10.scm')
-rw-r--r-- | module/srfi/srfi-10.scm | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/module/srfi/srfi-10.scm b/module/srfi/srfi-10.scm new file mode 100644 index 000000000..8e7181a3b --- /dev/null +++ b/module/srfi/srfi-10.scm @@ -0,0 +1,89 @@ +;;; srfi-10.scm --- Hash-Comma Reader Extension + +;; Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc. +;; +;; This library is free software; you can redistribute it and/or +;; modify it under the terms of the GNU Lesser General Public +;; License as published by the Free Software Foundation; either +;; version 2.1 of the License, or (at your option) any later version. +;; +;; This library 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 +;; Lesser General Public License for more details. +;; +;; You should have received a copy of the GNU Lesser General Public +;; License along with this library; if not, write to the Free Software +;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 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. +;; +;; This module is fully documented in the Guile Reference Manual. + +;;; Code: + +(define-module (srfi srfi-10) + :use-module (ice-9 rdelim) + :export (define-reader-ctor)) + +(cond-expand-provide (current-module) '(srfi-10)) + +;; 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) + +;;; srfi-10.scm ends here |