From 831297f162bbaa1e41e0937d2207df8a2532e9b8 Mon Sep 17 00:00:00 2001
From: simonpj <unknown>
Date: Tue, 16 Mar 1999 12:31:55 +0000
Subject: [PATCH] [project @ 1999-03-16 12:31:55 by simonpj] Make it only a
warning if you have a type like this:
forall a. Int -> Int
These show up in interface files occasionally, just because
the simplifier is a bit blase about adding type arguments.
But it's an error to have
forall a. Eq a => Int -> Int
The flag -fwarn-unused-matches reports a warning for these
redundant for-alls.
---
ghc/compiler/rename/RnSource.lhs | 28 +++++++++++++++++++++++-----
1 file changed, 23 insertions(+), 5 deletions(-)
diff --git a/ghc/compiler/rename/RnSource.lhs b/ghc/compiler/rename/RnSource.lhs
index 1dddb2291d9c..b43f6cbe4055 100644
--- a/ghc/compiler/rename/RnSource.lhs
+++ b/ghc/compiler/rename/RnSource.lhs
@@ -48,8 +48,10 @@ import PrelInfo ( derivingOccurrences, numClass_RDR,
bindIO_NAME
)
import Bag ( bagToList )
+import List ( partition )
import Outputable
import SrcLoc ( SrcLoc )
+import CmdLineOpts ( opt_WarnUnusedMatches ) -- Warn of unused for-all'd tyvars
import UniqFM ( lookupUFM )
import Maybes ( maybeToBool, catMaybes )
import Util
@@ -540,12 +542,19 @@ rnHsType doc (HsForAllTy (Just forall_tyvars) ctxt ty)
-- Explicit quantification.
-- Check that the forall'd tyvars are a subset of the
-- free tyvars in the tau-type part
+ -- That's only a warning... unless the tyvar is constrained by a
+ -- context in which case it's an error
= let
- mentioned_tyvars = extractHsTyVars ty
- bad_guys = filter (`notElem` mentioned_tyvars) forall_tyvar_names
- forall_tyvar_names = map getTyVarName forall_tyvars
+ mentioned_tyvars = extractHsTyVars ty
+ constrained_tyvars = [tv | (_,tys) <- ctxt,
+ ty <- tys,
+ tv <- extractHsTyVars ty]
+ dubious_guys = filter (`notElem` mentioned_tyvars) forall_tyvar_names
+ (bad_guys, warn_guys) = partition (`elem` constrained_tyvars) dubious_guys
+ forall_tyvar_names = map getTyVarName forall_tyvars
in
- mapRn (forAllErr doc ty) bad_guys `thenRn_`
+ mapRn (forAllErr doc ty) bad_guys `thenRn_`
+ mapRn (forAllWarn doc ty) warn_guys `thenRn_`
checkConstraints True doc forall_tyvar_names ctxt ty `thenRn` \ ctxt' ->
rnForAll doc forall_tyvars ctxt' ty
@@ -791,9 +800,18 @@ dupClassAssertWarn ctxt (assertion : dups)
badDataCon name
= hsep [ptext SLIT("Illegal data constructor name"), quotes (ppr name)]
+forAllWarn doc ty tyvar
+ | not opt_WarnUnusedMatches = returnRn ()
+ | otherwise
+ = addWarnRn (
+ sep [ptext SLIT("The universally quantified type variable") <+> quotes (ppr tyvar),
+ nest 4 (ptext SLIT("does not appear in the type") <+> quotes (ppr ty))]
+ $$
+ (ptext SLIT("In") <+> doc))
+
forAllErr doc ty tyvar
= addErrRn (
- sep [ptext SLIT("The universally quantified type variable") <+> quotes (ppr tyvar),
+ sep [ptext SLIT("The constrained type variable") <+> quotes (ppr tyvar),
nest 4 (ptext SLIT("does not appear in the type") <+> quotes (ppr ty))]
$$
(ptext SLIT("In") <+> doc))
--
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