[Haskell-cafe] GLR parser for Haskell?

Sven Panne svenpanne at gmail.com
Tue Apr 20 11:12:15 UTC 2021

Am Di., 20. Apr. 2021 um 12:57 Uhr schrieb Benjamin Redelings <
benjamin.redelings at gmail.com>:

> [...] I'm still curious about why the GHC parser does not use a grammar
> that
> is closer to the language grammar.  Is this mostly for historical
> reasons?  Are GLR parsers too slow?  I don't know what fraction of the
> compilation time is spent in parsing, but would suspect it is not that
> much.

I think there are various aspects:
   * Tool support (i.e. historic reasons): Happy is a LALR parser generator.
   * Quality of error reporting: I don't have a clue how good GLR parsers
are in this area. Often more powerful parsing methods have horrible
reporting, at least that's my impression.
   * Does the GLR parser generator detect ambiguities and report them to
the grammar writer? To me, ambiguities (like the shift/reduce &
reduce/reduce conflicts in LALR parsing) are a big red flag and a sign of a
questionable language/grammar: Even if the generator/parser is able to
figure things out correctly, humans have a much harder time.

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