[Haskell-cafe] Re: unification

[Christian Maeder]

andrea wrote:
>> data Tipo = Var Int | Const String | Tipo :-> Tipo deriving (Show, Eq)
>>

> But now how can I do to make the set of Const fixed??
> I want just a few base types, like "int" and "string", how could I
> define it?

your base types could be:

Const "String" :: Tipo

Const "Int" :: Tipo

and the polymorphic type of the identity function could be:

Var 1 :-> Var 1 :: Tipo

(and with "infixr :->") the type of binary function like (+)

Const "Int" :-> Const "Int" :-> Const "Int"

Note: the data type does not support type constructors like "List".

I recommend from:
 http://www.haskell.org/haskellwiki/Research_papers/Type_systems

Typing Haskell in Haskell

The first few pages will be enough (substitution is on page 7)

However, the link
http://www.cse.ogi.edu/~mpj/pubs/thih.html
does not work for me

Could someone correct that link?

Christian