Hi,
I've been looking at the Haskell parser in
ghc/compiler/GHC/Parser.y. It relies on post-processing pretty
heavily, both to determine the type of parsed expressions (i.e. is
"(x,y)" a pattern or expression?) and to reject invalid syntax
(i.e. field declarations are parsed as a type, but this is
rejected during postprocessing I think, except in constructor
declarations).
This makes the grammar rather hard to read. To quote [1]:
Instead of describing the language to be parsed, the grammar describes the process used to parse it; it's more like a hand-crafted parsing program, but crammed
into Backus-Naur Form.
Does anybody know if there is another version of the parser
generator uses grammar rules that are closer to the grammar rules
in the 2010 report? Maybe a GLR grammar?
Also, I see that Happy is able to generate GLR parsers. I'm curious if GLR parsers aren't being used just because they are slow, or if there is some other reason they are hard to use. I am not an expert on parsing or grammars, so any insight would be appreciated.
Thanks!
-BenRI