Re: Simple GADTs Question

[David Menendez]

J. Garrett Morris writes:

> Hello,
> 
> I'm attempting to use GADTs for the first time, and I'm running into
> an (I think) odd error.  My file includes:
> 
> data DFExpr :: * -> *
> where Deriv :: (Num t) => t -> Deriv Int (DFExpr t) (DFExpr t)

I think you want something like this:

Deriv :: Int -> DFExpr t -> DFExpr t -> DFExpr t

Ignorning the other clauses, it's equivalent to

data DFExpr t = Deriv Int (DFExpr t) (DFExpr t)
-- 
David Menendez <[EMAIL PROTECTED]> | "In this house, we obey the laws
  |of thermodynamics!"
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Simple GADTs Question

[J. Garrett Morris]

Hello,

I'm attempting to use GADTs for the first time, and I'm running into
an (I think) odd error.  My file includes:

data DFExpr :: * -> *
where Deriv :: (Num t) => t -> Deriv Int (DFExpr t) (DFExpr t)
  (:+:) :: (Num t) => DFExpr t -> DFExpr t -> DFExpr t
-- and so forth,
  DFFeat :: FExpr t

and I'm getting an error "Not in scope: type constructor or class
`Deriv'.  I've got -fglasgow-exts in the options - what else should I
be doing?

 /g
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