[NumericPrelude] Bug in Numeric Prelude or GHC?

Henning Thielemann lemming at henning-thielemann.de
Mon Jun 20 19:59:16 BST 2011

On Mon, 20 Jun 2011, Grigory Sarnitskiy wrote:

> a = Var "a"
> in ghci :
> *Main> -a :: Expression Float
> <interactive>:1:1:
>    No instance for (GHC.Num.Num (Expression Float))
>      arising from a use of syntactic negation
>    Possible fix:
>      add an instance declaration for (GHC.Num.Num (Expression Float))
>    In the expression: - a :: Expression Float
>    In an equation for `it': it = - a :: Expression Float

Is this a difference between GHCi and GHC? I know there is some syntactic 
sugar that does not work in GHCi, but works in GHC. I even think it was 
already reported somewhere, but I cannot find a GHC trac ticket.


More information about the Numeric-Prelude mailing list