#3731: SYB gone wild - mysterious <<loop>> in code derived from an
syb-with-class
example
---------------------------------+------------------------------------------
Reporter: dsf | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.12.1
Resolution: | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: Incorrect result at runtime
---------------------------------+------------------------------------------
Comment (by JeremyShaw):
I compiled with:
{{{ghc -S Bug.hs -ddump-simpl -dsuppress-uniques -dcore-lint}}}
And I get this:
{{{
Main.e :: Main.Expression
[GlobalId]
[]
Main.e =
case $dSat
`cast` ((Main.:Co:TSat) (Main.DefaultD Main.Expression)
:: (Main.:TSat) (Main.DefaultD Main.Expression)
~
Main.DefaultD Main.Expression)
of tpl { Main.DefaultD ipv ->
ipv
}
Rec {
$dSat :: Main.Sat (Main.DefaultD Main.Expression)
[GlobalId]
[]
$dSat = $dSat
end Rec }
}}}
It seems clear that the loop is caused by:
{{{$dSat = $dSat}}}
The question is whether the simplifier is causing the bug, or if the bug
already exists after desugaring/type checking, and the simplifier is doing
the right thing.
I also tried dumping the output after {{{-ddump-ds}}}. But I have not
studied it enough to figure out if it is doing the right thing or not.
This bug has popped up several different ways in our code base. :( Is
there something we can do to get it looked at by someone who might
understand what is going on?
thanks!
- jeremy
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3731#comment:3>
GHC <http://www.haskell.org/ghc/>
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