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

[ajb at spamcop.net]

G'day all.

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

> It is astonishing to see that your version actually performs the worst (at
> least on my machine).

On your example, I'm not surprised:

> plong 0 = Var 0
> plong n | even n    = Or  (Var n) (plong (n-1))
>         | otherwise = And (Var n) (plong (n-1))

This is effectively a singly linked list.  I would expect my (well, I
didn't invent it) to work better on something that didn't have this
unique structure, such as:

test 0 = Var 0
test n | even n    = Or  (Var n) (test (n-1))
        | otherwise = And (test (n-1)) (Var n)

Cheers,
Andrew Bromage