newtype pattern matching

[Feuer]

Please reply to dfeuer@cs.brown.edu


I don't remember if I answered this before, but...

I don't see the relevance of there being no constructor to match on.  That
is the case for any tuple type.  It seems that

newtype T1 [a1 a2 ...] =3D C1 ...
is the same as
data T2 [a1 a2 ...] =3D C2 !... !... !...

Except that pattern matching on C1 is like lazy pattern matching on C2.
Since newtype is supposed to be about efficiency, I am trying to
understand what makes this more efficient.  I have not yet seen any
explanation of this.

On 22 Jan 2002, Martin [ISO-8859-1] Norb=E4ck wrote:

> tis 2002-01-22 klockan 15.52 skrev Feuer:
> > Why is pattern matching on newtypes lazy?  Does this add to efficiency
> > somehow?  If not, it seems to be just another rule to keep straight.
>
> That's the difference between newtype and data. Newtypes are unboxed, so
> there is no constructor to match on. Pattern matching on newtypes is
> only a type-checker thing, the constructor doesn't exist.
>
> Regards,
>
> =09Martin
>
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