GHC accepts `data Foo where` in H2010 mode
|Reported by:||hvr||Owned by:|
|Type of failure:||GHC accepts invalid program||Test Case:|
|Related Tickets:||Differential Rev(s):|
According to the Haskell2010 report,
The grammar productions relevant for data declarations are the following:
topdecl → data [context =>] simpletype [= constrs] [deriving]
However, GHC 7.0.4/7.4.2/7.6.3/HEAD all happily compile the following Haskell module without any warning when using -XHaskell2010 -Wall, even though this is not valid Haskell2010 afaik:
module Foo where data Foo where
The trailing where in the data declaration is not valid Haskell2010 (without language extensions such as GADT).
At the very least, this divergence from the Haskell Report should be mentioned in 14.1.1. Divergence from Haskell 98 and Haskell 2010.