* Dmitry Bogatov [2014-09-17 23:48:49+0400] Sorry for followup, I found that problem is not in this function per-se, but in filtering one. Since I require formula to be complicated enough, I have to filter out simple ones, and simple ones gets constructed before any more complicated. I get all formulas only about P before it even touches Q. How can I speed things up? -- Set of hacks, that tries to formalize my opinion what -- good formula is. goodFormula :: Formula -> Bool goodFormula = \case (Function2 t x y) -> x /= y && goodFormula x && goodFormula y && case (x, y) of (Negation u, Negation v) -> u /= v (Negation u, y) -> u /= y (x, Negation v) -> x /=v (Function2 t' u' v', _) -> t' /= t' || ((y /= u') && (y /= v')) _ -> True (Negation x) -> goodFormula x _ -> True flenght :: Formula -> Int flenght fmt = case value fmt of Right _ -> 0 Left l -> length (toList l) main = do -- mapM_ print $ take (buildFormulas [P, Q, R] 7) print $ filter (\f -> goodFormula f && flenght f == 3) (buildFormulas [P, Q, R] 4) !! 1 -- print $ (buildFormulas [P, Q, R] 5) !! 1

Hello! I have following code:

buildFormulas :: [Variable] -> Int -> [Formula] buildFormulas vars 0 = map Var vars buildFormulas vars n = join $ forM [0 .. n - 1 ] $ \i -> do x <- buildFormulas vars i y <- buildFormulas vars (n - i - 1) z <- buildFormulas vars (n - 1) let t1 = case z of (Negation _) -> [] _ -> [Negation z] t1 ++ [conj x y, impl x y, disj x y]

It is correct, typechecks, but it is insanely slow (calculating take 35 (buildFormulas [P, Q, R] 5) hangs my computer).

My guess is that it builds too much before returning first results. Can you suggest more efficent way enumerate formulas of set of variables?

-- Best regards, Dmitry Bogatov , Free Software supporter, esperantisto and netiquette guardian. GPG: 54B7F00D