On Mon, 26 Feb 2007 23:41:14 -0600 (CST), you wrote: >Here's my second attempt at the code: >...
You've left out a bunch of constructors, and there are various other errors here and there. I think this will do what you want: > data ISine = > Sine Integer Integer Integer [Char] | > MetaSine Integer Integer Integer [ISine] > > letter (Sine _ _ _ l) = l > sub_sines (MetaSine _ _ _ xs) = xs > period (Sine p _ _ _) = p > period (MetaSine p _ _ _) = p > offset (Sine _ o _ _) = o > offset (MetaSine _ o _ _) = o > threshold (Sine _ _ t _) = t > threshold (MetaSine _ _ t _) = t > > on :: Integer -> ISine -> Bool > on time iSine = (mod (time-(offset iSine)) (period iSine)) < (threshold iSine) > > act :: Integer -> ISine -> [[Char]] > act time (MetaSine p o t s) = > if on time (MetaSine p o t s) > then foldr1 (++) (map (act time) (sub_sines (MetaSine p o t s))) > else [] > > act time (Sine p o t l) = > if on time (Sine p o t l) > then [letter (Sine p o t l)] > else [] But note that you have to write the equations for period, offset and threshold twice. If you want to avoid that, you can move the Sine/MetaSine discrimination into the "tail" of the data structure, something like this: > data ISineTail = > SineTail [Char] | > MetaTail [ISine] > > data ISine = ISine Integer Integer Integer ISineTail > > letter (ISine _ _ _ (SineTail l)) = l > sub_sines (ISine _ _ _ (MetaTail xs)) = xs > period (ISine p _ _ _) = p > offset (ISine _ o _ _) = o > threshold (ISine _ _ t _) = t > > on :: Integer -> ISine -> Bool > on time iSine = (mod (time-(offset iSine)) (period iSine)) < (threshold iSine) > > act :: Integer -> ISine -> [[Char]] > act time (ISine p o t (MetaTail s)) = > if on time (ISine p o t (MetaTail s)) > then foldr1 (++) (map (act time) (sub_sines (ISine p o t (MetaTail s)))) > else [] > > act time (ISine p o t (SineTail l)) = > if on time (ISine p o t (SineTail l)) > then [letter (ISine p o t (SineTail l))] > else [] Steve Schafer Fenestra Technologies Corp. http://www.fenestra.com/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
