Am Samstag, 15. Oktober 2005 08:31 schrieb Bulat Ziganshin:
Hello Haskell,
number of type definition statements in Haskell (data, type, newtype) is a bit too large. at least, newtype definition seems to be superfluous - it can be replaced by the same `data` definition:
newtype A = A Int and data A = A Int
is equal, excluding for internal representation.
This is not true. With newtype, A _|_ is _|_, with data, A _|_ is not _|_. But as far as I know, the above newtype declaration is equivalent to this: data A = A !Int
[...]
(moreover, i prefer something like `alias` to defining aliases for existing types, and `type` for defining new types, but i think it's a bit too late to complain about it :) )
I think that the newtype syntax is misleading. It suggests a similarity to data declarations which is not there. Take the above newtype declaration. The expression A n doesn't mean that something new is constructed. It just means a type conversion. Pattern matching with the pattern A n doesn't mean that a part of a data structure is extracted but it just means – a type conversion. So, in my opinion, it would be a lot better if newtype wouldn't use these pseudo data constructors. Best wishes, Wolfgang