Re: [Haskell-cafe] what is the fastest way to extract variables from a proposition?

plong 0 = Var 0 plong n | even n = Or (Var n) (plong (n-1)) | otherwise = And (Var n) (plong (n-1)) main = do print ((length ∘ vars) (plong 10000000)) real 0m3.290s user 0m3.152s sys 0m0.020s main = do print ((length ∘ vars_) (plong 10000000)) real 0m3.732s user 0m3.680s sys 0m0.024s -- vrsn=varsBromage main = do print ((length ∘ vrsn) (plong 10000000)) real 0m4.164s user 0m4.128s sys 0m0.008s ghc -fglasgow-exts -O2 ghc 6.8.2 @Andrew: It is astonishing to see that your version actually performs the worst (at least on my machine). By looking at your code I had also thought that yours would be the fastest in terms of runtime performance, it was also exactly what I tried but failed to get to here on my own. Maybe future ghc versions will change this in favour of your version. I would like to have someone test it on another machine though: fetch: svn co https://okitsune.svn.sourceforge.net/svnroot/okitsune . build: ghc -fglasgow-exts -O2 Common.hs Propositions.hs Test.hs testS: time ./a.out sert testH: time ./a.out hutton testB: time ./a.out bromage Best regards, Cetin Sert. On 21/02/2008, ajb@spamcop.net wrote:

G'day all.

Quoting Cetin Sert :

...

-- proposition data Prp a = Var a | Not (Prp a) | Or (Prp a) (Prp a) | And (Prp a) (Prp a) | Imp (Prp a) (Prp a) | Xor (Prp a) (Prp a) | Eqv (Prp a) (Prp a) | Cns Bool deriving (Show, Eq)

This is probably the fastest:

vars :: Prp a -> [a] vars p = vars' p [] where vars' (Var a) = (a:)

vars' (Not p) = vars' p

vars' (Or l r) = vars' l . vars' r {- etc -} vars' (Cns _) = id

Cheers, Andrew Bromage

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