Subtyping

[Fritz K Ruehr]

Frank Atanassow wrote:

> This is a situation where the explicit fixpoint datatype comes in handy:
> 
>   data Fix f = In (f (Fix f))
> 
>   ...
> 
> BTW, this is not a beginner, or even intermediate, Haskell programmer's
> technique.

For those who are interested in what exactly is or isn't a beginner or 
intermediate Haskell programmer's technique, I humbly offer the following

	<http://www.willamette.edu/~fruehr/haskell/evolution.html>

which includes examples of the afore-mentioned approach, along with many
others, from accumulating parameters to comonads.

Fair warning: tongue held firmly in cheek ...

  --  Fritz Ruehr
      fruehr@willamette.edu