Commit 3671d002 authored by Simon Peyton Jones's avatar Simon Peyton Jones
Browse files

Fix desguaring of bang patterns (Trac #8952)

A palpable bug, although one that will rarely bite
parent 791f4fa2
......@@ -586,8 +586,6 @@ tidy1 _ non_interesting_pat
--------------------
tidy_bang_pat :: Id -> SrcSpan -> Pat Id -> DsM (DsWrapper, Pat Id)
-- BangPatterns: Pattern matching is already strict in constructors,
-- tuples etc, so the last case strips off the bang for those patterns.
-- Discard bang around strict pattern
tidy_bang_pat v _ p@(ListPat {}) = tidy1 v p
......@@ -596,8 +594,7 @@ tidy_bang_pat v _ p@(PArrPat {}) = tidy1 v p
tidy_bang_pat v _ p@(ConPatOut {}) = tidy1 v p
tidy_bang_pat v _ p@(LitPat {}) = tidy1 v p
-- Discard lazy/par/sig under a bang
tidy_bang_pat v _ (LazyPat (L l p)) = tidy_bang_pat v l p
-- Discard par/sig under a bang
tidy_bang_pat v _ (ParPat (L l p)) = tidy_bang_pat v l p
tidy_bang_pat v _ (SigPatOut (L l p) _) = tidy_bang_pat v l p
......@@ -607,7 +604,10 @@ tidy_bang_pat v l (AsPat v' p) = tidy1 v (AsPat v' (L l (BangPat p)))
tidy_bang_pat v l (CoPat w p t) = tidy1 v (CoPat w (BangPat (L l p)) t)
-- Default case, leave the bang there:
-- VarPat, WildPat, ViewPat, NPat, NPlusKPat
-- VarPat, LazyPat, WildPat, ViewPat, NPat, NPlusKPat
-- For LazyPat, remember that it's semantically like a VarPat
-- i.e. !(~p) is not like ~p, or p! (Trac #8952)
tidy_bang_pat _ l p = return (idDsWrapper, BangPat (L l p))
-- NB: SigPatIn, ConPatIn should not happen
\end{code}
......
{-# LANGUAGE BangPatterns #-}
module Main where
main = print (case Nothing of
!(~(Just x)) -> "ok"
Nothing -> "bad")
......@@ -40,3 +40,4 @@ test('mc08', normal, compile_and_run, [''])
test('T5742', normal, compile_and_run, [''])
test('DsLambdaCase', when(compiler_lt('ghc', '7.5'), skip), compile_and_run, [''])
test('DsMultiWayIf', when(compiler_lt('ghc', '7.5'), skip), compile_and_run, [''])
test('T8952', normal, compile_and_run, [''])
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