98 lines
3.4 KiB
Scheme
98 lines
3.4 KiB
Scheme
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;;;; simplify-tree.scm --- utility functions for the PEG parser
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;;;;
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;;;; Copyright (C) 2010, 2011 Free Software Foundation, Inc.
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;;;;
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;;;; This library is free software; you can redistribute it and/or
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;;;; modify it under the terms of the GNU Lesser General Public
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;;;; License as published by the Free Software Foundation; either
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;;;; version 3 of the License, or (at your option) any later version.
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;;;;
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;;;; This library 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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;;;; Lesser General Public License for more details.
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;;;;
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;;;; You should have received a copy of the GNU Lesser General Public
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;;;; License along with this library; if not, write to the Free Software
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;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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;;;;
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(define-module (ice-9 peg simplify-tree)
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#:export (keyword-flatten context-flatten string-collapse)
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#:use-module (system base pmatch))
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(define-syntax single?
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(syntax-rules ()
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;;"Return #t if X is a list of one element."
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((_ x)
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(pmatch x
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((_) #t)
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(else #f)))))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;;;; POST-PROCESSING FUNCTIONS (TO CANONICALIZE MATCH TREES)
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Is everything in LST true?
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(define (andlst lst)
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(or (null? lst)
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(and (car lst) (andlst (cdr lst)))))
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;; Is LST a list of strings?
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(define (string-list? lst)
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(and (list? lst) (not (null? lst))
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(andlst (map string? lst))))
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;; Groups all strings that are next to each other in LST. Used in
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;; STRING-COLLAPSE.
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(define (string-group lst)
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(if (not (list? lst))
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lst
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(if (null? lst)
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'()
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(let ((next (string-group (cdr lst))))
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(if (not (string? (car lst)))
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(cons (car lst) next)
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(if (and (not (null? next))
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(list? (car next))
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(string? (caar next)))
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(cons (cons (car lst) (car next)) (cdr next))
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(cons (list (car lst)) next)))))))
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;; Collapses all the string in LST.
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;; ("a" "b" (c d) "e" "f") -> ("ab" (c d) "ef")
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(define (string-collapse lst)
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(if (list? lst)
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(let ((res (map (lambda (x) (if (string-list? x)
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(apply string-append x)
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x))
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(string-group (map string-collapse lst)))))
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(if (single? res) (car res) res))
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lst))
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;; If LST is an atom, return (list LST), else return LST.
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(define (mklst lst)
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(if (not (list? lst)) (list lst) lst))
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;; Takes a list and "flattens" it, using the predicate TST to know when to stop
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;; instead of terminating on atoms (see tutorial).
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(define (context-flatten tst lst)
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(if (or (not (list? lst)) (null? lst))
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lst
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(if (tst lst)
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(list lst)
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(apply append
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(map (lambda (x) (mklst (context-flatten tst x)))
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lst)))))
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;; Takes a list and "flattens" it, using the list of keywords KEYWORD-LST to
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;; know when to stop at (see tutorial).
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(define (keyword-flatten keyword-lst lst)
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(context-flatten
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(lambda (x)
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(if (or (not (list? x)) (null? x))
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#t
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(member (car x) keyword-lst)))
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lst))
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