[clean-list] Synonym types

[Arjen van Weelden]

Alan Hutchinson wrote:
 > Hello Arjen
 > Thanks for your mail.
 > It helps understand the matter, though I am still not sure
 > what to do about it.

Hello Alan,

If you want to use types in such a way, you will have to use algebraic 
or record types in Clean. Clean does not support something like 
Haskell's newtype.

You could try using a algebraic type or a record type. The record type 
run-time representation is similar to tuples.

	:: SynTypeA a b = {fst :: a, snd :: b}

	:: Constr t1 t2 a b = C (t1 a b) (t2 a b)

	:: SynTypeB a b :== Constr SynTypeA SynTypeA a b

	testFn :: SynTypeA Int String
	testFn = {fst = 3, snd = "It works."}

	Start = (fst, snd) where {fst, snd} = testFn

To simulate Haskell's newtype, because Clean does not (fully) support 
class instances for synonym types, you can also use a record with a 
single field. This is more efficient than an algebraic constructor.
Unfortunately, it does require more syntax.

regards,
	Arjen