tree grammar Optimizer;
options {
	language = Java;
	output = AST;
	tokenVocab = Arith;
	ASTLabelType = CommonTree;
}

@header{
package de.hshn.se.akse.ss09.parser;
}

//a program consists of zero or more statements
program : statement*;

//a statement can either be an assignment or an I/O Operation
statement
  : ^(ASSIGN ID expr) 
  | ^(READ ID) 
  | ^(WRITE expr)  
  ;
/*
All of the expression rules from the parser grammar collapse into a single recursive
rule in the tree grammar. The parser constructs ASTs for expressions
that encode the order of operations by their very structure. The
tree grammar does not need to repeat the multilevel expression grammar
pattern used by parser grammars to deal with different levels of
precedence. -- ANTLR The Definitive Reference p.202
*/ 
expr  
: ^(ADD a=expr b=expr)    //-> {$a.tree.toStringTree().equals("0")}? $a
                          //-> {$b.tree.toStringTree().equals("0")}? $b
                          //-> ^(ADD $a $b)
                          -> $a
| ^(MINUS a=expr b=expr)  -> {$b.tree.toStringTree().equals("0")}? $a
                          -> ^(MINUS $a $b)
| ^(MULT a=expr b=expr)   -> {$a.tree.toStringTree().equals("1")}? $a
                          -> {$b.tree.toStringTree().equals("1")}? $b
                          -> ^(MULT $a $b)
| ^(DIV a=expr b=expr)    -> {$a.tree.toStringTree().equals("0")}? $a
                          -> {$b.tree.toStringTree().equals("1")}? $a
                          -> ^(DIV $a $b)
| ID                      -> ID
| INT                     -> INT
| FLOAT                   -> FLOAT
| ZERO                    -> ZERO
;