tree grammar CalcWalker;

options
{
	tokenVocab = Calc;
	ASTLabelType = CommonTree;
}

@header
{
	import java.util.Map;
	import java.util.HashMap;
}

@members
{
	static private final Map<String,Double> registers = new HashMap<String,Double> ();
	static private double ans = 0;
}

program
	: stat+
	;

stat returns [double value]
	// mathemathical expression
	: expr
	{
	 $value = $expr.value;
	 ans = $expr.value;
	 System.out.println ("ans = " + $value);
	}
	// assignment
	| ^('=' REGISTER expr)
	{
	 $value = $expr.value;
	 ans = $expr.value;
	 System.out.println ($REGISTER.text + " = " + $value);
	 registers.put ($REGISTER.text, new Double (value));
	}
	;

expr returns [double value]
	// addition
	: ^('+' a=expr b=expr)		{ $value = $a.value + $b.value; }
	// subtraction
	| ^('-' a=expr b=expr)		{ $value = $a.value - $b.value; }
	// multiplication
	| ^('*' a=expr b=expr)		{ $value = $a.value * $b.value; }
	// division
	| ^('/' a=expr b=expr)		{ $value = $a.value / $b.value; }
	// power (indicy)
	| ^('**' a=expr b=expr)		{ $value = Math.pow ($a.value, $b.value); }
	// negation
	| ^(NEGATE a=expr)		{ $value = -$a.value; }
	// square root
	| ^('sqrt' a=expr)		{ $value = Math.sqrt ($a.value); }
	// absolute value
	| ^('abs' a=expr)		{ $value = Math.abs ($a.value); }
	// a number
	| NUMBER			{ $value = new Double ($NUMBER.text).doubleValue (); }
	// the previous answer
	| ANS				{ $value = ans; }
	// the value of a register
	| REGISTER
	{
	 if (!registers.containsKey ($REGISTER.text))
	 {
	  throw new Error ("Unknown register " + $REGISTER.text);
	 }
	 $value = registers.get ($REGISTER.text).doubleValue ();
	}
	;