class ExpressionParser extends Parser;
options { buildAST=true; }

imaginaryTokenDefinitions :
   SIGN_MINUS
   SIGN_PLUS
;

expr     : {System.out.println("trying expr");} LPAREN^ sumExpr RPAREN! {System.out.println("matched expr");};
sumExpr  : {System.out.println("trying sumExpr");} prodExpr ((PLUS^|MINUS^) prodExpr)* {System.out.println("matched sumExpr");};
prodExpr : {System.out.println("trying prodExpr");} powExpr ((MUL^|DIV^|MOD^) powExpr)* {System.out.println("matched prodExpr");};
powExpr  : {System.out.println("trying powExpr");} signExpr (POW^ signExpr)? {System.out.println("matched powExpr");} ;
signExpr : {System.out.println("trying signExpr");} (
         m:MINUS^ {#m.setType(SIGN_MINUS); System.out.println("matched signExpr");}
         |	p:PLUS^  {#p.setType(SIGN_PLUS); System.out.println("matched signExpr");}
         )? atom ;
atom     : {System.out.println("trying atom");} INT | expr {System.out.println("matched atom");};

class ExpressionLexer extends Lexer;

PLUS  : '+' ;
MINUS : '-' ;
MUL   : '*' ;
DIV   : '/' ;
MOD   : '%' ;
POW   : '^' ;
LPAREN: '(' ;
RPAREN: ')' ;
SEMI  : ';' ;
protected DIGIT : '0'..'9' ;
INT   : (DIGIT)+ ;

WS    : (' ' | '\t' | '\r' | '\n') {$setType(Token.SKIP);} ;

{import java.lang.Math;}
class ExpressionTreeWalker extends TreeParser;

expr returns [double r]
  { double a,b; r=0; }

  : #(PLUS  a=expr b=expr) { r=a+b; }
  | #(MINUS a=expr b=expr) { r=a-b; }
  | #(MUL   a=expr b=expr) { r=a*b; }
  | #(DIV   a=expr b=expr) { r=a/b; }
  | #(MOD   a=expr b=expr) { r=a%b; }
  | #(POW   a=expr b=expr) { r=Math.pow(a,b); }
  | #(LPAREN a=expr)       { r=a; }
  | #(SIGN_MINUS a=expr)   { r=-1*a; } 
  | #(SIGN_PLUS  a=expr)   { if(a<0)r=0-a; else r=a; }
  | i:INT { r=(double)Integer.parseInt(i.getText()); }
  ;