[haskell-cafe] Monad and kinds

[Tim Chevalier]

On 9/4/08, Jake Mcarthur <jake.mcarthur at gmail.com> wrote:
 >  Two lazy algorithms tend to compose well and result in a lazy
>  algorithm. A lazy algorithm can compose with a strict algorithm in two
>  different ways. One way is for the lazy algorithm to control the
>  strict algorithm, in which case the strict algorithm is either invoked
>  or not invoked, resulting in a lazy algorithm. The other way is for
>  the strict algorithm to control the lazy algorithm, in which case the
>  strict algorithm requests the data it needs from the lazy algorithm as
>  it needs it, resulting in a strict algorithm. Finally, two strict
>  algorithms may also compose, which results in a strict algorithm.
>
>  No matter how you slice it, none of the above scenarios are
>  necessarily bad. Each of the four permutations of laziness and
>  strictness for two composed algorithms are necessary for different
>  situations. Laziness and strictness work in tandem with each other to
>  construct whole programs.
>

You say lazy algorithms are good because they compose well. In
Haskell, does an algorithm that operates on data structures that have
strict components have that property?

>  We Haskellers like laziness by default because we find that it
>  encourages us to consider laziness to solve our problems more often
>  than in call-by-need languages, not because it is somehow "superior"
>  to strictness. That is the strongest argument I can think of to be
>  made in favor of lazy-by-default.
>

So you don't believe that laziness is superior to strictness, or
versa; I don't, either. But you do say it's good to be encouraged to
use laziness more often. Why? You mention compositionality above as a
possible reason, in reply to which, see above.

Cheers,
Tim

-- 
Tim Chevalier * http://cs.pdx.edu/~tjc * Often in error, never in doubt
"The future is not google-able." -- William Gibson