/* 

  Calc benchmark in Picat.

  From 
  http://www.jekejeke.ch/idatab/doclet/prod/en/docs/05_run/15_stdy/06_bench/09_programs/11_calc/01_calc.p.html

  This Picat model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/


% import util.
% import cp.


main => go.

go => calc.
go2 => calc.

/**
 * Prolog code for the DCG calculator.
 *
 * DCGs are a simple case of Colmerauers Metamorphosis grammars
 * an were presented to the community in the 1980 paper
 * Definite Clause Grammars for Language Analysis, by F.C.N.
 * Pereira and D.H.D. Warren.
 *
 * The DCG calculator is usually considered Prolog homework.
 *
 * Copyright 2011-2012, XLOG Technologies GmbH, Switzerland
 * Jekejeke Prolog 0.9.0 (a fast and small prolog interpreter)
 */

expr(Z) --> "-", !, term(X), {Y is -X}, expr_rest(Y,Z).
expr(Y) --> term(X), expr_rest(X,Y).

expr_rest(X,T) --> "+", !, term(Y), {Z is X+Y}, expr_rest(Z,T).
expr_rest(X,T) --> "-", !, term(Y), {Z is X-Y}, expr_rest(Z,T).
expr_rest(X,X) --> [].

term(Y) --> factor(X), term_rest(X,Y).

term_rest(X,T) --> "*", !, factor(Y), {Z is X*Y}, factor_rest(Z,T).
term_rest(X,T) --> "/", !, factor(Y), {Z is X/Y}, factor_rest(Z,T).
term_rest(X,X) --> [].

factor(X) --> "(", !, expr(X), ")".
factor(Y) --> digit(X), factor_rest(X,Y).

factor_rest(X,T) --> digit(Y), !, {Z is X*10+Y}, factor_rest(Z,T).
factor_rest(X,X) --> [].

% digit(Y) --> [X], {48=<X, X=<57, Y is X-48}.
digit(Y) --> [X], {ascii_digit(X), Y is X.to_int}.

calc :-
   % phrase(expr(_),"-12+34*56+78").
   expr(_,"-12+34*56+78",[]).
calc :-
   % phrase(expr(_),"(-12+34)*(56+78)").
   expr(_,"(-12+34)*(56+78)",[]).