1/*
    2* Copyright (c) 2016, University of Texas at Dallas
    3* All rights reserved.
    4*
    5* Redistribution and use in source and binary forms, with or without
    6* modification, are permitted provided that the following conditions are met:
    7*     * Redistributions of source code must retain the above copyright
    8*       notice, this list of conditions and the following disclaimer.
    9*     * Redistributions in binary form must reproduce the above copyright
   10*       notice, this list of conditions and the following disclaimer in the
   11*       documentation and/or other materials provided with the distribution.
   12*     * Neither the name of the University of Texas at Dallas nor the
   13*       names of its contributors may be used to endorse or promote products
   14*       derived from this software without specific prior written permission.
   15*
   16* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   17* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   18* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   19* DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OF TEXAS AT DALLAS BE LIABLE FOR
   20* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
   21* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   22* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
   23* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   24* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   25* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   26*/
   27
   28:- module(scasp_variables,
   29          [ is_var/1,
   30            is_var/2,
   31            body_vars/3,
   32            var_list/2,                 % +N, -Vars
   33            revar/3                     % +Term,-VarTerm,-Bindings
   34          ]).   35:- use_module(library(assoc)).   36:- use_module(library(apply)).   37:- use_module(library(lists)).   38
   39/** <module> Variable storage and access
   40
   41Predicates related to storing, accessing and modifying variables.
   42
   43@author Kyle Marple
   44@version 20170515
   45@license BSD-3
   46*/
   47
   48%!  is_var(@Term) is semidet.
   49%!  is_var(@Term, Name) is semidet.
   50%
   51% Test an entry to see if it's   a variable (the first non-underscore is
   52% an upper-case letter.
   53%
   54% @arg Term is the term to be tested.
   55
   56is_var($X) :-
   57    atom(X).
   58
   59is_var($X, X) :-
   60    atom(X).
   61
   62%!  body_vars(+Head:compound, +Body:list, -BodyVars:list) is det
   63%
   64%   Get the body variables (variables used in   the  body but not in the
   65%   head) for a clause.
   66
   67:- det(body_vars/3).   68
   69body_vars(H, B, Bv) :-
   70    empty_assoc(Empty),
   71    term_vars(H, _, [], Empty, Hv),
   72    term_vars(B, Bv, [], Hv, _).
   73
   74term_vars(Var, Vars0, Vars, Seen0, Seen) :-
   75    is_var(Var, Name),
   76    !,
   77    (   get_assoc(Name, Seen0, _)
   78    ->  Vars = Vars0,
   79        Seen = Seen0
   80    ;   put_assoc(Name, Seen0, true, Seen),
   81        Vars0 = [Var|Vars]
   82    ).
   83term_vars(Term, Vars0, Vars, Seen0, Seen) :-
   84    compound(Term),
   85    !,
   86    functor(Term, _Name, Arity),
   87    term_vars(1, Arity, Term, Vars0, Vars, Seen0, Seen).
   88term_vars(_, Vars, Vars, Seen, Seen).
   89
   90term_vars(I, Arity, Term, Vars0, Vars, Seen0, Seen) :-
   91    I =< Arity,
   92    !,
   93    arg(I, Term, Arg),
   94    term_vars(Arg, Vars0, Vars1, Seen0, Seen1),
   95    I2 is I+1,
   96    term_vars(I2, Arity, Term, Vars1, Vars, Seen1, Seen).
   97term_vars(_, _, _, Vars, Vars, Seen, Seen).
   98
   99%!  var_list(+N:int, -Vars:list) is det
  100%
  101%   Get a list of N variables, each   of  which is different. Basically,
  102%   just append a counter to '_X'.  The   '_'  prefix ensures they don't
  103%   overlap with any existing variables in a rule.
  104%
  105%   @arg  N The size of the list to return.
  106%   @arg  Vars output list.
  107
  108:- det(var_list/2).  109
  110var_list(0, []) :-
  111    !.
  112var_list(I, [H|T]) :-
  113    I2 is I-1,
  114    var_list(I2, T),
  115    mk_var(I2, H).
  116
  117mk_var(I, $Name) :-
  118    atom_concat('_X', I, Name).
  119
  120%!  revar(+Term, -VarTerm, -Bindings) is det.
  121%
  122%   If Term is  a  term  that   contains  atoms  using  variable  syntax
  123%   ([A-Z].*), VarTerm is a copy of Term with all such atoms replaced by
  124%   variables.   In addition this performs the following rewrites:
  125%
  126%     - A term N/D is translated into rat(N,D)
  127%     - An atom N/D is translated into rat(N,D)
  128%     - A quoted atom is translated into its unquoted equivalent
  129%
  130%   @arg Bindings is a list `Name=Var` that contains the variable names.
  131
  132revar(X,Y,VarNames) :-
  133    empty_assoc(Dic0),
  134    revar_(X,Y,Dic0,Dic),
  135    assoc_to_list(Dic, Pairs),
  136    maplist(varname, Pairs, VarNames).
  137
  138varname(Name-Var, Name=Var).
  139
  140revar_(X,Y,Dic,Dic) :-
  141    var(X),
  142    !,
  143    Y=X.
  144revar_(X,Y,Dic0,Dic) :-
  145    is_var(X, Name),
  146    !,
  147    (   get_assoc(Name, Dic0, Y)
  148    ->  Dic = Dic0
  149    ;   put_assoc(Name, Dic0, Y, Dic)
  150    ).
  151revar_(X,Y,Dic,Dic) :-
  152    special_atom(X,Y),
  153    !.
  154revar_(X,Y,Dic0,Dic) :-
  155    X=..[F|As],
  156    revars(As,Bs,Dic0,Dic),
  157    Y=..[F|Bs].
  158
  159special_atom(A/B,Rat) :-
  160    integer(A),
  161    integer(B),
  162    !,
  163    Rat is rdiv(A,B).
  164special_atom(X,Y) :-
  165    atom(X),
  166    atom_chars(X,Codes),
  167    append(['\''|C_Y],['\''],Codes),
  168    atom_chars(Y,C_Y).
  169
  170revars([],[],Dic,Dic).
  171revars([X|Xs],[Y|Ys],Dic0,Dic) :-
  172    revar_(X,Y,Dic0,Dic1),
  173    revars(Xs, Ys, Dic1, Dic)