PUBLIC
Thanks Simon!
Of course, you're right, it's the renamer, not the typechecker - I didn't
really check, just saw that "it happens during `typecheckModule`.
I'll look at the rebindable syntax stuff in detail, but at least for
OverloadedStrings, I already know that the problem will be that ultimately they
do go through the `String` type from `base`, and I need to use GHC baselessly.
This is a problem for two reasons:
* I can't implement `IsString` for `MyString`, because `IsString` is in
`base`
* Even if I made my own fake `base` with a fake `IsString` class, there is
nothing to put in the codomain of `fromString`: I *only* have `MyString`, not
`String`. And renaming `MyString to `String` in my fake `base` is not going to
cut it, since `String` is wired into GHC to be a type synonym for `[Char]`
(which `MyString` is not).
I foresee similar problems for OverloadedLists :/
Thanks,
Gergo
From: Simon Peyton Jones <simo...@microsoft.com>
Sent: Tuesday, July 6, 2021 5:08 PM
To: Erdi, Gergo <gergo.e...@sc.com>
Cc: GHC <ghc-devs@haskell.org>
Subject: [External] RE: Marking ParsedModule fragments as non-user-originating
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
<ghc-devs-boun...@haskell.org<mailto:ghc-devs-boun...@haskell.org>> On Behalf
Of Erdi, Gergo via ghc-devs
Sent: 06 July 2021 09:08
To: ghc-devs@haskell.org<mailto:ghc-devs@haskell.org>
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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