#2118: deriving for GRose
----------------------------------------------------+-----------------------
Reporter: alexey | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.8.2 | Severity: normal
Keywords: type classes, undecidable instances | Testcase:
Architecture: x86 | Os: MacOS X
----------------------------------------------------+-----------------------
GHC 6.6 used to be happy with the program below provided that i use
"-fglasgow-exts -fallow-undecidable-instances"
{{{
data GRose ff a = GRose a (ff (GRose ff a))
}}}
The same program does NOT work with GHC 6.8, 6.8.1 and 6.8.2, even if I
use the options "-fglasgow-exts -XUndecidableInstances". This is the error
I get:
{{{
No instance for (Show (ff (GRose ff a)))
arising from the 'deriving' clause of a data type declaration
at domotest.hs:2:0-56
Possible fix:
add an instance declaration for (Show (ff (GRose ff a)))
When deriving the instance for (Show (GRose ff a))
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2118>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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