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 <ajb@spamcop.net> wrote:
G'day all.


Quoting Cetin Sert <cetin.sert@gmail.com>:

> -- 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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