evan_tech -- haskell fun

09:08 am, 17 Jun 05

A short snippet of a haskell session.

I like this definition (which I likely borrowed from somewhere):
let fac n = scanl1 (*) [1..] !! (n-1)

scanl1 produces a list of repeatedly applying the operation to elements in the list. So scanl1 (*) [1..n] provides factorials from 2 to n.
scanl1 (*) [1..], then, is the infinite list of factorials. (Values are only generated once they're asked for...)
And !! is the "get the nth element" operator.

So this code is basically: n factorial is the nth element in the list of all factorials.

It memoizes itself! (I think?)

theorb	BTW, for comparisign, the idomatic perl6 way to define factorial is sub fac($x) {[] 1..$x} If you want the closest equiv, it'd be &fac ::= -> $x {([] 1..)[$x]}. -> $x {...} as a lambda, with a parameter named $x. ::= is a compile-time binding. You should be able to figure out the rest.
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gaal That however does not memoize itself. :)

(But no doubt there'll be a standard is Memoized trait)

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gaal	That however does not memoize itself. :) (But no doubt there'll be a standard is Memoized trait)
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