| semantics). In doing so, I've come across an oddity. It seems
| that Haskell does not have the principal type property
It looks to me that you are correct. I hadn't realised that consequence
of the dreaded M.R.It may be "well known in the Haskell community",
it wasn't well known to me.
J
Oops!
I said THIH has problems with type synonyms. That is completely wrong.
I meant type SIGNATURES and nothing else. Sorry for the confusion.
/kff
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Hi Karl-Filip,
> (Mark Jones's THIH algorithm, as
> well as other algorithms built on W, fails to type some programs
> containing type synonyms).
Are you thinking of the following kind of problem?
type T a = Bool
b :: Eq a => T a
b = True
x = b
Gives in Hugs:
Type checking
ERROR "Test
Hello again!
John Hughes suggested that Haskell should have two forms of binding,
one with call-by-name (does not preserve sharing) semantics and
polymorphism and overloading and monomorphic with call-by-need
(preserves sharing).
The question is; would this restore principal types in general?
So here is the offending program:
class IsNil a where
isNil :: a -> Bool
instance IsNil [b] where
isNil [] = True
isNil _ = False
f x y = let g = isNil
in (g x, g y)
The monomorphism restriction applies to
Hi all!
I've been spending some time the last year writing up a formalization
of the Haskell type system (actually, most of the static semantics).
In doing so, I've come across an oddity. It seems that Haskell does not
have the principal type property, ie there are Haskell expressions
which, in
