The typechecker now complains that the `ViewPatterns` language extension is not
turned on
I think it's the renamer:
rnPatAndThen mk p@(ViewPat _ expr pat)
= do { liftCps $ do { vp_flag <- xoptM LangExt.ViewPatterns
; checkErr vp_flag (badViewPat p) }
More generally, don't you just want OverloadedStrings or OverloadedLists?
You might want to read Note [Handling overloaded and rebindable constructs] in
GHC.Rename.Expr, and
Note [Rebindable syntax and HsExpansion] in GCH.Hs.Expr. These Notes describe
how GHC already does something similar to what you want. Maybe you can use
the same mechanism in your plugin.
Simon
From: ghc-devs <[email protected]> On Behalf Of Erdi, Gergo via
ghc-devs
Sent: 06 July 2021 09:08
To: [email protected]
Subject: Marking ParsedModule fragments as non-user-originating
PUBLIC
Hi,
I'd like to hijack some syntax (like string literals or list patterns) for my
own use, and I thought a low-tech way of doing that is to transform the
ParsedModule before typechecking. For example, if I have a function `uncons ::
Array a -> Maybe (a, Array a)`, I can rewrite the pattern `[x1, x2, x3]` into
the view pattern `(uncons -> Just (x1, (uncons -> Just (x2, (uncons -> Just
(x3, (uncons -> Nothing)))))))` and let the normal GHC type checker take over
from here.
This is working for me so far, except for one problem: the typechecker now
complains that the `ViewPatterns` language extension is not turned on. I would
like to make the view patterns coming from my ParsedModule rewriter to be
exempt from this check (but of course still require the `ViewPatterns`
extension for user-originating code). Is there a way to do that? Or would I be
better off checking for user-originating view patterns myself before the
rewrite and then changing the `DynFlags` to always enable view patterns for
typechecking?
Thanks,
Gergo
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