[In ghc-2.10 and ghc-3.01]
The ghc version of the ST module
ghc/lib/exts/ST.lhs
makes (ST s) a Monad but not a Functor.
In hugs 1.4 February it is both a Monad and a Functor.
I don't know where to look for a formal definition for these extension
libraries, but I think hugs is right and that the Functor instance should
be there.
Patrik Jansson
------------------------------------------------------------------------
import ST
main = print (runST (map id (return True)))
STtest.hs:2: No instance for: `Functor (ST taLs)'
arising from use of `map' at STtest.hs:2
In a polymorphic function argument `(map id (return True))'
In the first argument of `runST', namely `(map id (return True))'
In the first argument of `print', namely
`(runST (map id (return True)))'
Compilation had errors
