ParserFilter suggestion

John Cowan cowan at
Fri Jul 31 17:57:21 BST 1998

Ron Bourret scripsit:
> Currently, SetParser in ParserFilter accepts a single parser.  I think this
> should be a Stack of parsers.  Each ParserFilter would set its own parser to the
> top parser on the stack, pop that off, and pass the rest of the Stack to the
> next level down.  This would allow the application to build a stack of
> ParserFilters, each performing a different operation.

That was my intent in making ParserFilter a subinterface of Parser.
Here's how an application can do what you want:

	Parser p;
	ParserFilter pf;
	p = new RealParser();
	pf = new FooFilter();
	p = pf;
	pf = new BarFilter();
	p = pf;
	pf = new BazFilter();
	p = pf;

If setParser returned "this" rather than void, then you could write the
cascade in fewer lines:

	Parser p = new RealParser();
	ParserFilter pf = new FooFilter().setParser(p);
	pf = new BarFilter().setParser(pf);
	pf = new BazFilter().setParser(pf);
	p = pf;

I will probably make that change to setParser.

John Cowan		cowan at
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

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