#3911: HughesPJ.vcat should behave like 'foldr ($$) empty', not like 'foldr
($+$)
empty'
---------------------------------+------------------------------------------
Reporter: benedikt | Owner:
Type: bug | Status: new
Priority: normal | Component: libraries/pretty
Version: 6.12.1 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: Incorrect result at runtime
---------------------------------+------------------------------------------
The performance tuning for libraries/pretty applied in June 2008
{{{
Tue Jun 24 12:37:15 BST 2008 [email protected]
* fillNB bug, lazy vcat
}}}
accidentally changed the behavior of vcat to {{{foldr ($+$) empty}}},
although it should be {{{foldr ($$) empty}}}, according to the
documentation. Fixing this is simple (patch attached).
{{{
hunk ./Text/PrettyPrint/HughesPJ.hs 497
-vcat = reduceAB . foldr (above_' True) empty
+vcat = reduceAB . foldr (above_' False) empty
}}}
See:
http://www.haskell.org/pipermail/libraries/2008-December/011032.html
http://www.haskell.org/pipermail/libraries/2010-March/013067.html
It would be nice to add a test case, but I'm not sure where to put it.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3911>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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