On Thu, 13 May 2004, Dan Sugalski wrote:
>
> The big problem is that I don't know *how* to implement a mixed-type
> parser generator. I'm not big on parsers in general, so I'm mostly
> stuck with the literature if I need to write one from scratch.
I have been thinking the following about what larry said earlier. Is this
what you meant, larry?
$grammar = q{
class_defn: "class" block .. etc (normal top-down stuff)
...
term: { call Parse::Yapp or something }
}
What I mean by that weird pseudocode is that everything happens in a
parse-recdescent parser, except that the production of some non-terminals
calls into a bottom-up parser. That part seems trivially doable. What I
need to figure out is how the bottom-up parser can relinquish control to
the top-down parser if it hits a block or such.
A preliminary thought: A traditional bottom-up parser can take the four
actions shift, reduce, accept, and error. We will need a fifth: call the
top down parser. I have not thought through how that happens or if it can
be done at all. It is the only way that I currently see.
I think I'll try to coax Parse::Recdescent and Parse::Yapp to work
together. I have never used the latter, but the documentation seems to
suggest that it can do what Bison can. Or maybe I should write two small
parsers by hand (one recdescent and the other an operator precedence
shift/reduce) and make them be nice to each other.
--abhijit
