1/*  Part of SWI-Prolog
   2
   3    Author:        Jan Wielemaker
   4    E-mail:        J.Wielemaker@vu.nl
   5    WWW:           http://www.swi-prolog.org
   6    Copyright (c)  2010-2011, University of Amsterdam
   7    All rights reserved.
   8
   9    Redistribution and use in source and binary forms, with or without
  10    modification, are permitted provided that the following conditions
  11    are met:
  12
  13    1. Redistributions of source code must retain the above copyright
  14       notice, this list of conditions and the following disclaimer.
  15
  16    2. Redistributions in binary form must reproduce the above copyright
  17       notice, this list of conditions and the following disclaimer in
  18       the documentation and/or other materials provided with the
  19       distribution.
  20
  21    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  25    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  29    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  31    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  32    POSSIBILITY OF SUCH DAMAGE.
  33*/
  34
  35:- module(rewrite,
  36          [ rewrite/2,                  % +Rule, +Input
  37            rew_term_expansion/2,
  38            rew_goal_expansion/2,
  39
  40            op(1200, xfx, (::=))
  41          ]).
  42:- use_module(library(quintus)).
  43
  44:- meta_predicate
  45    rewrite(1, +).
  46
  47                 /*******************************
  48                 *          COMPILATION         *
  49                 *******************************/
  50
  51rew_term_expansion((Rule ::= RuleBody), (Head :- Body)) :-
  52    translate(RuleBody, Term, Body0),
  53    simplify(Body0, Body),
  54    Rule =.. [Name|List],
  55    Head =.. [Name,Term|List].
  56
  57rew_goal_expansion(rewrite(To, From), Goal) :-
  58    nonvar(To),
  59    To = \Rule,
  60    callable(Rule),
  61    Rule =.. [Name|List],
  62    Goal =.. [Name,From|List].
  63
  64
  65                 /*******************************
  66                 *            TOPLEVEL          *
  67                 *******************************/
  68
  69%!  rewrite(:To, +From)
  70%
  71%   Invoke the term-rewriting system
  72
  73rewrite(M:T, From) :-
  74    (   var(T)
  75    ->  From = T
  76    ;   T = \Rule
  77    ->  Rule =.. [Name|List],
  78        Goal =.. [Name,From|List],
  79        M:Goal
  80    ;   match(T, M, From)
  81    ).
  82
  83match(Rule, M, From) :-
  84    translate(Rule, From, Code),
  85    M:Code.
  86
  87translate(Var, Var, true) :-
  88    var(Var),
  89    !.
  90translate((\Command, !), Var, (Goal, !)) :-
  91    !,
  92    (   callable(Command),
  93        Command =.. [Name|List]
  94    ->  Goal =.. [Name,Var|List]
  95    ;   Goal = rewrite(\Command, Var)
  96    ).
  97translate(\Command, Var, Goal) :-
  98    !,
  99    (   callable(Command),
 100        Command =.. [Name|List]
 101    ->  Goal =.. [Name,Var|List]
 102    ;   Goal = rewrite(\Command, Var)
 103    ).
 104translate(Atomic, Atomic, true) :-
 105    atomic(Atomic),
 106    !.
 107translate(C, _, Cmd) :-
 108    command(C, Cmd),
 109    !.
 110translate((A, B), T, Code) :-
 111    (   command(A, Cmd)
 112    ->  !, translate(B, T, C),
 113        Code = (Cmd, C)
 114    ;   command(B, Cmd)
 115    ->  !, translate(A, T, C),
 116        Code = (C, Cmd)
 117    ).
 118translate(Term0, Term, Command) :-
 119    functor(Term0, Name, Arity),
 120    functor(Term, Name, Arity),
 121    translate_args(0, Arity, Term0, Term, Command).
 122
 123translate_args(N, N, _, _, true) :- !.
 124translate_args(I0, Arity, T0, T1, (C0,C)) :-
 125    I is I0 + 1,
 126    arg(I, T0, A0),
 127    arg(I, T1, A1),
 128    translate(A0, A1, C0),
 129    translate_args(I, Arity, T0, T1, C).
 130
 131command(0, _) :-                       % catch variables
 132    !,
 133    fail.
 134command({A}, A).
 135command(!, !).
 136
 137                 /*******************************
 138                 *            SIMPLIFY          *
 139                 *******************************/
 140
 141%!  simplify(+Raw, -Simplified)
 142%
 143%   Get rid of redundant `true' goals generated by translate/3.
 144
 145simplify(V, V) :-
 146    var(V),
 147    !.
 148simplify((A0,B), A) :-
 149    B == true,
 150    !,
 151    simplify(A0, A).
 152simplify((A,B0), B) :-
 153    A == true,
 154    !,
 155    simplify(B0, B).
 156simplify((A0, B0), C) :-
 157    !,
 158    simplify(A0, A),
 159    simplify(B0, B),
 160    (   (   A \== A0
 161        ;   B \== B0
 162        )
 163    ->  simplify((A,B), C)
 164    ;   C = (A,B)
 165    ).
 166simplify(X, X).
 167
 168                 /*******************************
 169                 *             XREF             *
 170                 *******************************/
 171
 172:- multifile
 173    prolog:called_by/2.
 174
 175prolog:called_by(rewrite(Spec, _Term), Called) :-
 176    findall(G+1, sub_term(\G, Spec), Called).