Marc van Dongen writes:
>
..
>
> The following program:
>
> > module Main( main ) where
> > main = putStr (seq bot "1\n") >>
> > return ()
> > where bot = error []
>
> cannot be compiled:
> Main.lhs:1: Ambiguous context `{PrelBase.Eval tans}'
> `PrelBase.Eval tans' arising from use of `Prelude.seq' at Main.lhs:4
>
Hi,
this seems like a fair response to me (modulo the use of 'tans' rather
than 'a'), 'bot' has type alpha, but 'seq' requires its first argument
to be an instance of Eval.
>
> The folowing program
>
> > module Main( main ) where
> > main = putStr (seq bot "1\n") >>
> > return ()
> > where bot | 0 == 1 = []
>
> outputs:
>
> 1
This time bot has type '[alpha]' for which there is an Eval instance,
i.e., evaluate the list to WHNF.
HTH,
--Sigbjorn
