On Sat, Dec 22, 2007 at 10:22:46PM +0100, alpheccar wrote:

Can someone confirm me that:

type TA = A :+: B type TB = C :+: D type T = TA :+: TB

is not equivalent to

type T = A :+: B :+: C :+: D

where I have defined

infixr 6 :+: data (f :+: g) data A data B data C data D

I have a computation at type level which is working with the later definition of T but not with the former (ghc 6.8.1)

Type synonyms are implicitly parenthetized, and your :+: is non-associative. Compare: s +:+ t = concat["(",s,",",t,")"] foo = "a" +:+ "b" bar = "c" +:+ "d" baz = (foo +:+ bar) == ("a" +:+ "b" +:+ "c" +:+ "d") Stefan

alpheccar wrote:

Can someone confirm me that:

type TA = A :+: B type TB = C :+: D type T = TA :+: TB

This is type T = (A :+: B) :+: (C :+: D)

is not equivalent to

type T = A :+: B :+: C :+: D

is type T = A :+: (B :+: (C :+: D)) So these types are indeed not the same. Twan