'deriving Data' compilation regression 6.10.1 -> 6.12.1
Compiling the attached file in GHC 6.12.1 gives the following error, when GHC 6.10.1 compiles it fine:
[1 of 1] Compiling Main ( baddata.hs, baddata.o )
baddata.hs:33:14:
No instances for (Data Const, Data Var)
arising from the 'deriving' clause of a data type declaration
at baddata.hs:33:14-17
Possible fix:
add an instance declaration for (Data Const, Data Var)
or use a standalone 'deriving instance' declaration instead,
so you can specify the instance context yourself
When deriving the instance for (Data (Domain e g))