Maybe -XLiberalTypeSynonyms is an option:
http://www.haskell.org/ghc/docs/6.12.2/html/users_guide/data-type-extensions...
On 29 September 2010 20:08, DavidA
Hi,
I have the following code:
{-# LANGUAGE TypeSynonymInstances #-}
data Vect k b = V [(k,b)] -- vector space over field k with basis b -- for example, V [(5, E 1), (7, E 2)] would represent the vector 5 e1 + 7 e2
data Monomial v = M [(v,Int)] -- monomials over variables v -- for example, M [(A,3), (B,5)] would represent the monomial a^3 b^5
type Poly k v = Vect k (Monomial v) -- multivariate polynomials over field k and variables v
instance Monad (Poly k) where return v = V [(1, M [(v,1)])] p >>= f = ... -- variable substitution
So my thinking is: 1. The Monad type class is for one parameter type constructors (eg [], IO) 2. Poly is a two-parameter type constructor 3. So Poly k is a one-parameter type constructor 4. What I'm trying to express, that polynomials over field k are a monad, is true.
However, GHC 6.12.2 complains:
Type synonym `Poly' should have 2 arguments, but has been given 1 In the instance declaration for `Monad (Poly k)'
What is going wrong?
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