[antlr-interest] Re: Example for Micheal (was: When does AST construction go through factory?)

[Daniel Gackle]

Micheal,

While we're at it, I just ran into a third problem.  I added a class called
IntNode to the calc.g example from my previous post, and changed the "atom"
rule to do this:

atom:	INT<AST=IntNode>;

In other words I made what I believe you referred to as a "per-tokenref
mapping".  The generated code looks right:

tmp6_AST = (IntNode) astFactory.create(LT(1), "IntNode");

But it generates a run time exception: "System.InvalidCastException:
Specified cast is not valid."  Keep in mind that in order to get this to
compile I had to get astFactory.create() to accept LT(1) as an int.  To do
this I added the following temporary workaround code to ASTFactory.cs:

/// <summary>Added by dg</summary>
public static implicit operator int(Token t)
{
	return t.Type;
}

That's all for now.  Below is the full text of the "modified modified
calc.g".

Daniel

///////////////////////////////////////////////////
// Start of modified Calc.g ver.2

options {
	language = "CSharp";
}

class CalcParser extends Parser;
options {
	buildAST = true;	// uses CommonAST by default
}

tokens {
	EXPR<AST=ExprNode>;
	STAR<AST=StarNode>;
}

{
	public class StarNode { }
	public class ExprNode { }
	public class IntNode { }
}

expr
	:	mexpr (PLUS^ mexpr)* SEMI!
		{ ## = #(#[EXPR,"EXPR"], ##); }
	;

mexpr
	:	atom (STAR^ atom)*
	;

atom:	INT<AST=IntNode>
	;

class CalcLexer extends Lexer;

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

LPAREN:	'('
	;

RPAREN:	')'
	;

STAR:	'*'
	;

PLUS:	'+'
	;

SEMI:	';'
	;

protected
DIGIT
	:	'0'..'9'
	;

INT	:	(DIGIT)+
	;

class CalcTreeWalker extends TreeParser;

expr returns [float r]
{
	float a,b;
	r=0;
}
	:	#(PLUS a=expr b=expr)	{r = a+b;}
	|	#(STAR a=expr b=expr)	{r = a*b;}
	|	i:INT			{r = Convert.ToSingle(i.getText());}
	;

// End of modified Calc.g ver.2
///////////////////////////////////////////////////


 

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