[Haskell-cafe] Re: Channel9 Interview: Software Composability and theFu ture of Languages

[Bill Wood]

On Wed, 2007-01-31 at 19:51 +1100, Donald Bruce Stewart wrote:
   . . .
>     foldl (\water dish -> wash water dish) soapywater dishes :: [Dishes]

Nice example.  First, note that you can't get close with map -- you need
accumulation across the dishes.  Second, the correctness of this plan
depends on the rather strong frame axiom that no entity in the
environment is changed during a step of the fold, so no broken dishes.
Finally, that doesn't work so well when there are constraints on the
order that the dishes are washed, for example when washing the cruddiest
dishes first while there are more suds.

 -- Bill Wood