367 lines
11 KiB
Prolog
367 lines
11 KiB
Prolog
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/*************************************************************************
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* *
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* YAP Prolog *
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* *
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* Yap Prolog was developed at NCCUP - Universidade do Porto *
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* *
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* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997 *
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* *
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**************************************************************************
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* *
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* File: arith.yap *
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* Last rev: *
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* mods: *
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* comments: arithmetical optimization *
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* *
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*************************************************************************/
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% the default mode is on
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%% @file arith.yap
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:- system_module( '$_arith', [compile_expressions/0,
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expand_exprs/2,
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plus/3,
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succ/2], ['$c_built_in'/4]).
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:- private( [do_c_built_in/3,
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do_c_built_metacall/3,
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expand_expr/3,
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expand_expr/5,
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expand_expr/6] ).
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:- use_system_module( '$_errors', ['$do_error'/2]).
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:- use_system_module( '$_modules', ['$clean_cuts'/2]).
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/** @defgroup CompilerAnalysis Internal Clause Rewriting
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@ingroup YAPCompilerSettings
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@{
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YAP supports several clause optimisation mechanisms, that
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are designed to improve execution of arithmetic
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and term construction built-ins. In other words, during the
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compilation process a clause is rewritten twice:
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1. first, perform user-defined goal_expansion as described
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in the predicates goal_expansion/1 and goal_expansion/2.
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2. Perform expansion of some built-ins like:
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+ pruning operators, like ->/2 and *->/2
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+ arithmetic, including early evaluation of constant expressions
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+ specialise versions for some built-ins, if we are aware of the
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run-time execution mode
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The user has control over this process, through
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built-ins and through prolog flags.
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*/
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/** @pred expand_exprs(- _O_,+ _N_)
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Control term expansion during compilation.
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Enables low-level optimizations. It reports the current state by
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unifying _O_ with the previous state. It then puts YAP in state _N_
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(`on` or `off`)/ _On_ is equivalent to compile_expressions/0 and `off`
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is equivalent to do_not_compile_expressions/0.
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This predicate is useful when debugging, to ensure execution close to the original source.
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*/
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expand_exprs(Old,New) :-
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(get_value('$c_arith',true) ->
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Old = on ;
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Old = off ),
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'$set_arith_expan'(New).
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'$set_arith_expan'(on) :- set_value('$c_arith',true).
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'$set_arith_expan'(off) :- set_value('$c_arith',[]).
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/** @pred compile_expressions
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After a call to this predicate, arithmetical expressions will be compiled.
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(see example below). This is the default behavior.
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*/
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compile_expressions :- set_value('$c_arith',true).
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/** @pred do_not_compile_expressions
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After a call to this predicate, arithmetical expressions will not be compiled.
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~~~~~~~
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?- source, do_not_compile_expressions.
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yes
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?- [user].
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| p(X) :- X is 2 * (3 + 8).
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| :- end_of_file.
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?- compile_expressions.
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yes
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?- [user].
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| q(X) :- X is 2 * (3 + 8).
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| :- end_of_file.
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:- listing.
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p(A):-
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A is 2 * (3 + 8).
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q(A):-
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A is 22.
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~~~~~~~
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*/
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do_not_compile_expressions :- set_value('$c_arith',[]).
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'$c_built_in'(IN, M, H, OUT) :-
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get_value('$c_arith',true), !,
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'$yap_strip_module'(M:IN, M1, G1),
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do_c_built_in(G1, M1, H, OUT).
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'$c_built_in'(IN, _, _H, IN).
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do_c_built_in(G1, M1, H, OUT) :-
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var(G1), !,
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do_c_built_metacall(G1, M1, H, OUT).
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do_c_built_in(G1, M1, H, OUT) :-
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var(M1), !,
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do_c_built_metacall(G1, M1, H, OUT).
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do_c_built_in('$do_error'( Error, Goal), M, Head,
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throw(error(Error,[errorGoal=Goal, errorCaller=Head,prologPredFile=File,prologPredLine=Line,
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prologPredModule=M,prologPredName=Name,prologPredArity=Ar])))
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:-
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!,source_location(File, Line).
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do_c_built_in(system_error( Error, Goal), M, Head, ErrorG) :-
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!,
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do_c_built_in('$do_error'( Error, Goal), M, Head, ErrorG).
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do_c_built_in(X is Y, M, H, P) :-
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primitive(X), !,
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do_c_built_in(X =:= Y, M, H, P).
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do_c_built_in(X is Y, M, H, (P,A=X)) :-
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nonvar(X), !,
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do_c_built_in(A is Y, M, H, P).
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do_c_built_in(X is Y, _, _, P) :-
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nonvar(Y), % Don't rewrite variables
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!,
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(
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number(Y) ->
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P = ( X = Y); % This case reduces to an unification
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expand_expr(Y, P0, X0),
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'$drop_is'(X0, X, P0, P)
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).
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do_c_built_in(phrase(NT,Xs), Mod, H, NTXsNil) :-
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!,
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'$_arith':do_c_built_in(phrase(NT,Xs,[]), Mod, H, NTXsNil).
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do_c_built_in(phrase(NT,Xs0,Xs), Mod, _, NewGoal) :-
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!,
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'$c_built_in_phrase'(NT, Xs0, Xs, Mod, NewGoal ).
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do_c_built_in(Comp0, _, _, R) :- % now, do it for comparisons
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'$compop'(Comp0, Op, E, F),
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!,
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'$compop'(Comp, Op, U, V),
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expand_expr(E, P, U),
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expand_expr(F, Q, V),
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'$do_and'(P, Q, R0),
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'$do_and'(R0, Comp, R).
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do_c_built_in(P, _M, _H, P).
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do_c_built_metacall(G1, Mod, _, '$execute_wo_mod'(G1,Mod)) :-
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var(Mod), !.
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do_c_built_metacall(G1, Mod, _, '$execute_in_mod'(G1,Mod)) :-
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atom(Mod), !.
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do_c_built_metacall(G1, Mod, _, call(Mod:G1)).
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'$do_and'(true, P, P) :- !.
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'$do_and'(P, true, P) :- !.
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'$do_and'(P, Q, (P,Q)).
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% V is the result of the simplification,
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% X the result of the initial expression
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% and the last argument is how we are writing this result
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'$drop_is'(V, V1, P0, G) :-
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var(V),
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!, % usual case
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V = V1,
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P0 = G.
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'$drop_is'(V, X, P0, P) :- % atoms
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'$do_and'(P0, X is V, P).
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% Table of arithmetic comparisons
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'$compop'(X < Y, < , X, Y).
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'$compop'(X > Y, > , X, Y).
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'$compop'(X=< Y,=< , X, Y).
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'$compop'(X >=Y, >=, X, Y).
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'$compop'(X=:=Y,=:=, X, Y).
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'$compop'(X=\=Y,=\=, X, Y).
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'$composed_built_in'(V) :- var(V), !,
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fail.
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'$composed_built_in'(('$current_choice_point'(_),NG,'$$cut_by'(_))) :- !,
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'$composed_built_in'(NG).
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'$composed_built_in'((_,_)).
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'$composed_built_in'((_;_)).
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'$composed_built_in'((_|_)).
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'$composed_built_in'((_->_)).
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'$composed_built_in'(_:G) :-
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'$composed_built_in'(G).
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'$composed_built_in'(\+G) :-
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'$composed_built_in'(G).
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'$composed_built_in'(not(G)) :-
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'$composed_built_in'(G).
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% expanding an expression:
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% first argument is the expression not expanded,
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% second argument the expanded expression
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% third argument unifies with the result from the expression
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expand_expr(V, true, V) :-
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var(V), !.
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expand_expr([T], E, V) :- !,
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expand_expr(T, E, V).
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expand_expr(String, _E, V) :-
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string( String ), !,
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string_codes(String, [V]).
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expand_expr(A, true, A) :-
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atomic(A), !.
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expand_expr(T, E, V) :-
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T =.. [O, A], !,
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expand_expr(A, Q, X),
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expand_expr(O, X, V, Q, E).
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expand_expr(T, E, V) :-
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T =.. [O, A, B], !,
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expand_expr(A, Q, X),
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expand_expr(B, R, Y),
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expand_expr(O, X, Y, V, Q, S),
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'$do_and'(R, S, E).
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% expanding an expression of the form:
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% O is Op(X),
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% after having expanded into Q
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% and giving as result P (the last argument)
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expand_expr(Op, X, O, Q, Q) :-
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number(X),
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!,
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catch(is( O, Op, X),Error,bad_expr(Error,[Op, X])), !.
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% do not do error handling at compile time
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expand_expr(Op, X, O, Q, P) :-
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'$unary_op_as_integer'(Op,IOp),
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'$do_and'(Q, is( O, IOp, X), P).
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% expanding an expression of the form:
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% O is Op(X,Y),
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% after having expanded into Q
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% and giving as result P (the last argument)
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% included is some optimization for:
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% incrementing and decrementing,
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% the elementar arithmetic operations [+,-,*,//]
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expand_expr(Op, X, Y, O, Q, Q) :-
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number(X), number(Y),
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catch(is( O, Op, X, Y),Error,bad_expr(Error,[Op, X, Y ])), !.
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expand_expr(+, X, Y, O, Q, P) :- !,
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'$preprocess_args_for_commutative'(X, Y, X1, Y1, E),
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'$do_and'(E, '$plus'(X1,Y1,O), F),
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'$do_and'(Q, F, P).
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expand_expr(-, X, Y, O, Q, P) :-
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var(X), number(Y),
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Z is -Y, !,
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expand_expr(+, Z, X, O, Q, P).
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expand_expr(-, X, Y, O, Q, P) :- !,
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'$preprocess_args_for_non_commutative'(X, Y, X1, Y1, E),
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'$do_and'(E, '$minus'(X1,Y1,O), F),
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'$do_and'(Q, F, P).
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expand_expr(*, X, Y, O, Q, P) :- !,
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'$preprocess_args_for_commutative'(X, Y, X1, Y1, E),
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'$do_and'(E, '$times'(X1,Y1,O), F),
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'$do_and'(Q, F, P).
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expand_expr(//, X, Y, O, Q, P) :-
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nonvar(Y), Y == 0, !,
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'$binary_op_as_integer'(//,IOp),
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'$do_and'(Q, is(O,IOp,X,Y), P).
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expand_expr(//, X, Y, O, Q, P) :- !,
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'$preprocess_args_for_non_commutative'(X, Y, X1, Y1, E),
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'$do_and'(E, '$div'(X1,Y1,O), F),
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'$do_and'(Q, F, P).
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expand_expr(/\, X, Y, O, Q, P) :- !,
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'$preprocess_args_for_commutative'(X, Y, X1, Y1, E),
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'$do_and'(E, '$and'(X1,Y1,O), F),
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'$do_and'(Q, F, P).
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expand_expr(\/, X, Y, O, Q, P) :- !,
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'$preprocess_args_for_commutative'(X, Y, X1, Y1, E),
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'$do_and'(E, '$or'(X1,Y1,O), F),
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'$do_and'(Q, F, P).
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expand_expr(<<, X, Y, O, Q, P) :-
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var(X), number(Y), Y < 0,
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Z is -Y, !,
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expand_expr(>>, X, Z, O, Q, P).
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expand_expr(<<, X, Y, O, Q, P) :- !,
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'$preprocess_args_for_non_commutative'(X, Y, X1, Y1, E),
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'$do_and'(E, '$sll'(X1,Y1,O), F),
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'$do_and'(Q, F, P).
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expand_expr(>>, X, Y, O, Q, P) :-
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var(X), number(Y), Y < 0,
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Z is -Y, !,
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expand_expr(<<, X, Z, O, Q, P).
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expand_expr(>>, X, Y, O, Q, P) :- !,
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'$preprocess_args_for_non_commutative'(X, Y, X1, Y1, E),
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'$do_and'(E, '$slr'(X1,Y1,O), F),
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'$do_and'(Q, F, P).
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expand_expr(Op, X, Y, O, Q, P) :-
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'$binary_op_as_integer'(Op,IOp),
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'$do_and'(Q, is(O,IOp,X,Y), P).
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'$preprocess_args_for_commutative'(X, Y, X, Y, true) :-
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var(X), var(Y), !.
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'$preprocess_args_for_commutative'(X, Y, X, Y, true) :-
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var(X), integer(Y), \+ '$bignum'(Y), !.
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'$preprocess_args_for_commutative'(X, Y, X, Z, Z = Y) :-
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var(X), !.
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'$preprocess_args_for_commutative'(X, Y, Y, X, true) :-
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integer(X), \+ '$bignum'(X), var(Y), !.
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'$preprocess_args_for_commutative'(X, Y, Z, X, Z = Y) :-
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integer(X), \+ '$bignum'(X), !.
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'$preprocess_args_for_commutative'(X, Y, Z, W, E) :-
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'$do_and'(Z = X, Y = W, E).
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'$preprocess_args_for_non_commutative'(X, Y, X, Y, true) :-
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var(X), var(Y), !.
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'$preprocess_args_for_non_commutative'(X, Y, X, Y, true) :-
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var(X), integer(Y), \+ '$bignum'(Y), !.
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'$preprocess_args_for_non_commutative'(X, Y, X, Z, Z = Y) :-
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var(X), !.
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'$preprocess_args_for_non_commutative'(X, Y, X, Y, true) :-
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integer(X), \+ '$bignum'(X), var(Y), !.
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'$preprocess_args_for_non_commutative'(X, Y, X, Z, Z = Y) :-
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integer(X), \+ '$bignum'(X), !.
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'$preprocess_args_for_non_commutative'(X, Y, Z, W, E) :-
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'$do_and'(Z = X, Y = W, E).
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'$goal_expansion_allowed'(phrase(NT,_Xs0,_Xs), Mod) :-
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callable(NT),
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atom(Mod).
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%% contains_illegal_dcgnt(+Term) is semidet.
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%
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% True if Term contains a non-terminal we cannot deal with using
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% goal-expansion. The test is too general an approximation, but safe.
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'$contains_illegal_dcgnt'(NT) :-
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functor(NT, _, A),
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between(1, A, I),
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arg(I, NT, AI),
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nonvar(AI),
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( AI = ! ; AI = phrase(_,_,_) ), !.
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% write(contains_illegal_nt(NT)), % JW: we do not want to write
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% nl.
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'$harmless_dcgexception'(instantiation_error). % ex: phrase(([1],x:X,[3]),L)
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'$harmless_dcgexception'(type_error(callable,_)). % ex: phrase(27,L)
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:- set_value('$c_arith',true).
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/**
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@}
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*/
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