Python from Wise Guy's Viewpoint

Dirk Thierbach dthierbach at gmx.de
Mon Nov 3 06:00:14 EST 2003


prunesquallor at comcast.net wrote:
> Joachim Durchholz <joachim.durchholz at web.de> writes:

>> I'm still hoping for an explanation on the practical relevance of that
>> black hole device.

> Neel Krishnaswami had a wonderful explanation in article
> <slrnbplpv6.ikr.neelk at gs3106.sp.cs.cmu.edu>

And note that his example for practical relevance includes a datatype.

Haskell doesn't support recursive types directly, but a recursive
datatype for lists is easy:

data List a = Nil | Cons a (List a) 

Since Haskell is lazy, that's already a lazy list, but even if Haskell
was eager, you could write a similar datatype for lazy lists.
(And of course Haskell lists are essentially just given by the above
datatype, together with some syntactic sugar).

It's very natural for a relevant application of recursive types to
be coupled with data. 

- Dirk








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