Re: simple Haskell help needed on #19746

Hello Richard, Just FYI `gather` doesn't work with `readS_to_P` (throws an error), so you'll have to stick to ReadP parsers but, hopefully, that's OK. -Iavor On Tue, Apr 27, 2021 at 7:14 PM Richard Eisenberg wrote:

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On Apr 27, 2021, at 3:32 PM, Sebastian Graf wrote:

Hi Richard,

Maybe I lack a bit of context, but I don't see why you wouldn't choose (3). Extending the lexer/parser will yield a declarative specification of what exactly constitutes a GHC_OPTIONS pragma (albeit in a language that isn't Haskell) and should be more efficient than `reads`, even if you fix it to scale linearly. Plus, it seems that's what we do for other pragmas such as RULE already.

(3) is tempting indeed. There are two problems:

A. The code that parses strings isn't actually declarative. See https://gitlab.haskell.org/ghc/ghc/-/blob/d2399a46a01a6e46c831c19e797e656a0b.... In particular note the comment: "This stuff is horrible. I hates it." Evidently written by Simon M in 2003 with the introduction of alex.

B. We need this code outside the lexer, to deal with e.g. :set in GHCi.

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On Apr 27, 2021, at 4:28 PM, Iavor Diatchki wrote:

... gather ...

Aha! That was the magic incantation I needed but did not have. Many thanks, Iavor.

The curious can see https://gitlab.haskell.org/ghc/ghc/-/merge_requests/5509/diffs?commit_id=a56... for the final result.

Thanks! Richard _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs