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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Yes, that’s wrong. Thank you. Now fixed; see
<a href="http://hackage.haskell.org/trac/ghc/ticket/4918">http://hackage.haskell.org/trac/ghc/ticket/4918</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users-bounces@haskell.org]
<b>On Behalf Of </b>José Pedro Magalhães<br>
<b>Sent:</b> 18 January 2011 10:33<br>
<b>To:</b> GHC users<br>
<b>Subject:</b> Behavior of the inliner on imported class methods<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">Hello all,<br>
<br>
I fail to understand the behavior of the inliner in the following example:<o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">module M1 where<br>
<br>
class MyEnum a where myEnum :: [a]<br>
<br>
instance MyEnum () where myEnum = [()]<o:p></o:p></span></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">module M2 where<br>
<br>
import M1<br>
<br>
f1 = map (\() -> 'p') [()]<br>
f2 = map (\() -> 'q') myEnum<o:p></o:p></span></p>
</blockquote>
<p class="MsoNormal" style="margin-bottom:12.0pt"><br>
The generated core code for M2 with ghc-7.0.1 -O is:<o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">M2.f22 :: GHC.Types.Char<br>
[GblId,<br>
Caf=NoCafRefs,<br>
Str=DmdType m,<br>
Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,<br>
ConLike=True, Cheap=True, Expandable=True,<br>
Guidance=IF_ARGS [] 1 2}]<br>
M2.f22 = GHC.Types.C# 'q'<br>
<br>
M2.f11 :: GHC.Types.Char<br>
[GblId,<br>
Caf=NoCafRefs,<br>
Str=DmdType m,<br>
Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,<br>
ConLike=True, Cheap=True, Expandable=True,<br>
Guidance=IF_ARGS [] 1 2}]<br>
M2.f11 = GHC.Types.C# 'p'<br>
<br>
M2.f21 :: () -> GHC.Types.Char<br>
[GblId,<br>
Arity=1,<br>
Caf=NoCafRefs,<br>
Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=1, Value=True,<br>
ConLike=True, Cheap=True, Expandable=True,<br>
Guidance=ALWAYS_IF(unsat_ok=True,boring_ok=True)}]<br>
M2.f21 =<br>
\ (ds_dch :: ()) -> case ds_dch of _ { () -> M2.f22 }<br>
<br>
M2.f2 :: [GHC.Types.Char]<br>
[GblId,<br>
Str=DmdType,<br>
Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=False,<br>
ConLike=False, Cheap=False, Expandable=False,<br>
Guidance=IF_ARGS [] 3 0}]<br>
M2.f2 =<br>
GHC.Base.map<br>
@ () @ GHC.Types.Char M2.f21 M1.$fMyEnum()_$cmyEnum<br>
<br>
M2.f1 :: [GHC.Types.Char]<br>
[GblId,<br>
Caf=NoCafRefs,<br>
Str=DmdType,<br>
Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,<br>
ConLike=True, Cheap=True, Expandable=True,<br>
Guidance=IF_ARGS [] 1 3}]<br>
M2.f1 =<br>
GHC.Types.:<br>
@ GHC.Types.Char M2.f11 (GHC.Types.[] @ GHC.Types.Char)<o:p></o:p></span></p>
<p class="MsoNormal"><br>
So, why does the inliner fail to get rid of the map in f2, while correctly ditching it in f1? Note that using two modules is essential here: if the instance is in M2 (and thus becoming orphan), the inliner works "correctly". Adding INLINE/INLINABLE pragmas
to myEnum doesn't improve things either. Is this a bug, or is there a reason for this behavior?<br>
<br>
<br>
Thanks,<br>
Pedro<o:p></o:p></p>
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