[Haskell-cafe] Re: type trickery

[oleg at okmij.org]

Adrian Neumann wrote:

> I figured I'd need something like this

> data GF = GF Integer Integer

> so that each element of the finite field would remember p. However I
> can't think of a way to use the typesystem to ensure that p is always
> the same. 

You might like:

	Vectro: Haskell library for "statically typed linear algebra"
	http://ofb.net/~frederik/stla/

which marks each element of a vector space with its dimension. The
type system makes sure that you can only add vectors of the same
dimension (the type system does even more: it computes the dimension
of a result of multiplying a vector by a non-square matrix, for
example).

> I think that would need an infinite number of different types,
You think correctly. Haskell already has the infinite number of different
types (e.g., the infinite number of function types).