Parser.y rewrite with parser combinators

[Simon Peyton Jones]

We all love strong guarantees offered by type checking, but somehow most people shy away from "syntactic type checking" offered by parser generators. Parser combinators are the Python of parsing: Easy to use initially, but a maintenance hell in the long run for larger projects...
I’d never thought of it that way before – interesting.

Simon

From: ghc-devs <ghc-devs-bounces at haskell.org> On Behalf Of Sven Panne
Sent: 09 October 2018 08:23
To: vlad.z.4096 at gmail.com
Cc: GHC developers <ghc-devs at haskell.org>
Subject: Re: Parser.y rewrite with parser combinators

Am Di., 9. Okt. 2018 um 00:25 Uhr schrieb Vladislav Zavialov <vlad.z.4096 at gmail.com<mailto:vlad.z.4096 at gmail.com>>:
[...] That's true regardless of implementation technique, parsers are rather
delicate.

I think it's not the parsers themselves which are delicate, it is the language that they should recognize.

A LALR-based parser generator does provide more information
when it detects shift/reduce and reduce/reduce conflicts, but I never
found this information useful. It was always quite the opposite of
being helpful - an indication that a LALR parser could not handle my
change and I had to look for workarounds. [...]

Not that this would help at this point, but: The conflicts reported by parser generators like Happy are *extremely* valuable, they hint at tricky/ambiguous points in the grammar, which in turn is a strong hint that the language you're trying to parse has dark corners. IMHO every language designer and e.g. everybody proposing a syntactic extension to GHC should try to fit this into a grammar for Happy *before* proposing that extension. If you get conflicts, it is a very strong hint that the language is hard to parse by *humans*, too, which is the most important thing to consider. Haskell already has tons of syntactic warts which can only be parsed by infinite lookahead, which is only a minor technical problem, but a major usablity problem. "Programs are meant to be read by humans and only incidentally for computers to execute." (D.E.K.) </rant> ;-)

The situation is a bit strange: We all love strong guarantees offered by type checking, but somehow most people shy away from "syntactic type checking" offered by parser generators. Parser combinators are the Python of parsing: Easy to use initially, but a maintenance hell in the long run for larger projects...

Cheers,
   S.
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