[Haskell-cafe] using mutable data structures in pure functions
stephen.tetley at gmail.com
Mon Mar 12 09:09:28 CET 2012
There is a "trick" to `nub` where you couldn't implement the internal
lookup list with an (assumed faster) search tree anyway.
`nub` only mandates equality not ordering, so building a ordered
structure like a binary tree is impossible. In practice i would be
hard to beat list as the intermediate structure in this case.
On 12 March 2012 03:38, E R <pc88mxer at gmail.com> wrote:
> For example, consider the definition of Data.List.nub:
> nub l = nub' l 
> nub'  _ = 
> nub' (x:xs) ls
> | x `elem` ls = nub' xs ls
> | otherwise = x : nub' xs (x:ls)
> Clearly the memory allocated to ls never escapes nub', so it seems
> that ls could be replaced with a mutable data structure (with an eye
> towards improving performance in special cases).
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