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<br>
<br><br><div class="gmail_quote">On Wed, Sep 30, 2009 at 5:47 AM, wren ng thornton <span dir="ltr"><<a href="mailto:wren@freegeek.org">wren@freegeek.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="im">Olex P wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
This idea with new level of abstraction is good but in some cases it can<br>
make things overcomplicated / less efficient. Does that mean "leave simple<br>
built-in types as is"?<br>
</blockquote>
<br></div>
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]<br>
<br>
<br>
<br>
[1] By "strange ways" of providing typeclass instances I mean things like using<br>
<br>
class Peano p where ...<br>
<br>
data Z = Z<br>
newtype S n = S n<br>
instance Peano Z where ...<br>
instance Peano n => Peano (S n) where ...<br>
<br>
instead of a straightforward<br>
<br>
data ZorS = Z | S Peano<br>
instance Peano ZorS where ...<br>
<br>
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)).<br>
<br>
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.<br><font color="#888888">
<br>
-- <br>
Live well,<br>
~wren<br>
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