Parser.y rewrite with parser combinators

[Vladislav Zavialov]

It's a nice way to look at the problem, and we're facing the same
issues as with insufficiently powerful type systems. LALR is the Go of
parsing in this case :)

I'd rather write Python and have a larger test suite than deal with
lack of generics in Go, if you allow me to take the analogy that far.

In fact, we do have a fair share of boilerplate in our current grammar
due to lack of parametrisation. That's another issue that would be
solved by parser combinators (or by a fancier parser generator, but
I'm not aware of such one).

On Tue, Oct 9, 2018 at 1:52 PM Simon Peyton Jones <simonpj at microsoft.com> wrote:
>
> 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>:
>
> [...] 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.