#5783: Data.Text.isPrefixOf fails to terminate
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Reporter: reinerp | Owner:
Type: bug | Status: closed
Priority: highest | Milestone: 7.4.1
Component: Compiler | Version: 7.4.1-rc1
Resolution: invalid | Keywords:
Os: MacOS X | Architecture: x86_64 (amd64)
Failure: Incorrect result at runtime | Difficulty: Unknown
Testcase: | Blockedby:
Blocking: | Related:
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Changes (by simonmar):
* status: new => closed
* resolution: => invalid
Comment:
In `Data.Text` there is this:
{{{
-- | /O(n)/ The 'isPrefixOf' function takes two 'Text's and returns
-- 'True' iff the first is a prefix of the second. Subject to fusion.
isPrefixOf :: Text -> Text -> Bool
isPrefixOf a@(Text _ _ alen) b@(Text _ _ blen) =
alen <= blen && S.isPrefixOf (stream a) (stream b)
{-# INLINE [1] isPrefixOf #-}
{-# RULES
"TEXT isPrefixOf -> fused" [~1] forall s t.
isPrefixOf s t = S.isPrefixOf (stream s) (stream t)
"TEXT isPrefixOf -> unfused" [1] forall s t.
S.isPrefixOf (stream s) (stream t) = isPrefixOf s t
#-}
}}}
It looks to me like GHC has applied the second rewrite rule to end up with
{{{
isPrefixOf a@(Text _ _ alen) b@(Text _ _ blen) =
alen <= blen && isPrefixOf a b
}}}
which is an infinite loop when `alen > blen`.
So I don't think this is a bug, but the `text` package will need to be
fixed. Maybe this is going wroing now because we're optimising INLINE
functions after capturing their definitions, whereas we weren't before.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5783#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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