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* srfi-19.scm, srfi-17.scm, srfi-16.scm, srfi-14.scm, srfi-13.scm, srfi-11.scm, srfi-10.scm, srfi-9.scm, srfi-8.scm, srfi-6.scm, srfi-2.scm: Use `cond-expand-provide' for providing features to `cond-expand'.
87 lines
2.7 KiB
Scheme
87 lines
2.7 KiB
Scheme
;;;; srfi-10.scm --- SRFI-10 read hash extension for Guile
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;;;;
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;;;; Copyright (C) 2001 Free Software Foundation, Inc.
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;;;;
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;;;; This program is free software; you can redistribute it and/or
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;;;; modify it under the terms of the GNU General Public License as
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;;;; published by the Free Software Foundation; either version 2, or
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;;;; (at your option) any later version.
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;;;;
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;;;; This program is distributed in the hope that it will be useful,
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;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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;;;; General Public License for more details.
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;;;;
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;;;; You should have received a copy of the GNU General Public License
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;;;; along with this software; see the file COPYING. If not, write to
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;;;; the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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;;;; Boston, MA 02111-1307 USA
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;;; Commentary:
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;;; This module implements the syntax extension #,(), also called
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;;; hash-comma, which is defined in SRFI-10.
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;;;
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;;; The support for SRFI-10 consists of the procedure
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;;; `define-reader-ctor' for defining new reader constructors and the
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;;; read syntax form
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;;;
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;;; #,(<ctor> <datum> ...)
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;;;
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;;; where <ctor> must be a symbol for which a read constructor was
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;;; defined previously.
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;;;
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;;; Example:
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;;;
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;;; (define-reader-ctor 'file open-input-file)
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;;; (define f '#,(file "/etc/passwd"))
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;;; (read-line f)
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;;; =>
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;;; "root:x:0:0:root:/root:/bin/bash"
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;;;
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;;; Please note the quote before the #,(file ...) expression. This is
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;;; necessary because ports are not self-evaluating in Guile.
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;;; Code:
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(define-module (srfi srfi-10)
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#:use-module (ice-9 rdelim))
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(export define-reader-ctor)
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(cond-expand-provide (current-module) '(srfi-10))
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;; This hash table stores the association between comma-hash tags and
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;; the corresponding constructor procedures.
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;;
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(define reader-ctors (make-hash-table 31))
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;; This procedure installs the procedure @var{proc} as the constructor
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;; for the comma-hash tag @var{symbol}.
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;;
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(define (define-reader-ctor symbol proc)
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(hashq-set! reader-ctors symbol proc)
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(if #f #f)) ; Return unspecified value.
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;; Retrieve the constructor procedure for the tag @var{symbol} or
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;; throw an error if no such tag is defined.
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;;
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(define (lookup symbol)
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(let ((p (hashq-ref reader-ctors symbol #f)))
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(if (procedure? p)
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p
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(error "unknown hash-comma tag " symbol))))
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;; This is the actual reader extension.
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;;
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(define (hash-comma char port)
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(let* ((obj (read port)))
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(if (and (list? obj) (positive? (length obj)) (symbol? (car obj)))
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(let ((p (lookup (car obj))))
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(let ((res (apply p (cdr obj))))
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res))
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(error "syntax error in hash-comma expression"))))
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;; Install the hash extension.
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;;
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(read-hash-extend #\, hash-comma)
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