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| author | Sebastian Graf <sebastian.graf@kit.edu> | 2019-10-25 11:20:48 +0200 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2019-10-28 09:22:35 -0400 |
| commit | e951f219597a3e8209abd62f85c717865f7445ca (patch) | |
| tree | f1036c6a31758fb835179fc147ab4830c0b61c20 /compiler/GHC/Hs/Lit.hs | |
| parent | e0e0485634d9a047b43da958c09e3bf6c5937c0f (diff) | |
| download | haskell-e951f219597a3e8209abd62f85c717865f7445ca.tar.gz | |
Use FlexibleInstances for `Outputable (* p)` instead of match-all instances with equality constraints
In #17304, Richard and Simon dicovered that using `-XFlexibleInstances`
for `Outputable` instances of AST data types means users can provide orphan
`Outputable` instances for passes other than `GhcPass`.
Type inference doesn't currently to suffer, and Richard gave an example
in #17304 that shows how rare a case would be where the slightly worse
type inference would matter.
So I went ahead with the refactoring, attempting to fix #17304.
Diffstat (limited to 'compiler/GHC/Hs/Lit.hs')
| -rw-r--r-- | compiler/GHC/Hs/Lit.hs | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/compiler/GHC/Hs/Lit.hs b/compiler/GHC/Hs/Lit.hs index ab30de87ac..963bf0e2c0 100644 --- a/compiler/GHC/Hs/Lit.hs +++ b/compiler/GHC/Hs/Lit.hs @@ -9,6 +9,7 @@ {-# LANGUAGE TypeSynonymInstances #-} {-# LANGUAGE StandaloneDeriving #-} {-# LANGUAGE FlexibleContexts #-} +{-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE UndecidableInstances #-} -- Note [Pass sensitive types] -- in module GHC.Hs.PlaceHolder {-# LANGUAGE ConstraintKinds #-} @@ -227,7 +228,7 @@ instance Ord OverLitVal where compare (HsIsString _ _) (HsFractional _) = GT -- Instance specific to GhcPs, need the SourceText -instance p ~ GhcPass pass => Outputable (HsLit p) where +instance Outputable (HsLit (GhcPass p)) where ppr (HsChar st c) = pprWithSourceText st (pprHsChar c) ppr (HsCharPrim st c) = pp_st_suffix st primCharSuffix (pprPrimChar c) ppr (HsString st s) = pprWithSourceText st (pprHsString s) @@ -249,8 +250,8 @@ pp_st_suffix NoSourceText _ doc = doc pp_st_suffix (SourceText st) suffix _ = text st <> suffix -- in debug mode, print the expression that it's resolved to, too -instance (p ~ GhcPass pass, OutputableBndrId p) - => Outputable (HsOverLit p) where +instance OutputableBndrId p + => Outputable (HsOverLit (GhcPass p)) where ppr (OverLit {ol_val=val, ol_witness=witness}) = ppr val <+> (whenPprDebug (parens (pprExpr witness))) ppr (XOverLit x) = ppr x |