True. But anyway newtype creates a new type which is not what I'm looking
for. In this case instead of passing a string "myAttrName" user should pass
constructor as well. And the next step of such "simplification" will be a
smart constructor attrName? :) And that's all just to show user of that
function what kind of parameters function expects! :-D
On Wed, Sep 30, 2009 at 5:47 AM, wren ng thornton
Olex P wrote:
This idea with new level of abstraction is good but in some cases it can make things overcomplicated / less efficient. Does that mean "leave simple built-in types as is"?
That's what newtypes are for. A newtype is like a type alias, except that it is type checked. All newtype wrappering/unwrappering is compiled away so the representations are the same. The only performance difference is (== should be) that there can be overhead for strange ways of providing typeclass instances.[1]
[1] By "strange ways" of providing typeclass instances I mean things like using
class Peano p where ...
data Z = Z newtype S n = S n instance Peano Z where ... instance Peano n => Peano (S n) where ...
instead of a straightforward
data ZorS = Z | S Peano instance Peano ZorS where ...
Because of the newtype, the representation of (S n) is the same as the representation of Z, thus all peano numbers are the same size. However, we still need to keep that info around somewhere, and consequently the size of the (Peano n) dictionary is linear in n (because it needs a pointer to the (Peano (n-1)) dictionary, and so on until (Peano Z)).
On the other hand, with the straightforward version, the size of (n :: ZorS) is linear in n, but the size of the (Peano ZorS) dictionary is constant.
-- Live well, ~wren _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe