[Haskell-cafe] Equality constraints in type families

Hugo Pacheco hpacheco at gmail.com
Tue Mar 11 07:03:17 EDT 2008

I know I do not need these constraints, it was just the simplest way I found
to explain the problem.

I have fought about that: I was not expecting F d c ~  F a (c,a) not mean
that F d ~F a /\ c ~(c,a), I thought the whole family was "parameterized".
If I encoded the family

type family F a x :: *

F d c ~  F a (c,a) would be semantically different, meaning that this
"decomposition rule" does not apply?

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