Small tips: - Use swap and avoid those if's. - [a] ++ b is the same as a : b. - Factor out the first point that is always there. - Factor out line' arguments that don't change with the recursion. Untested:
swap :: Bool -> (a,a) -> (a,a) swap False = id swap True = \(x,y) -> (y,x)
line :: Point -> Point -> [Point] line (xa,ya) (xb,yb) = line' p1 p2 deltax deltay ystep isSteep 0 where isSteep = abs (yb - ya) > abs (xb - xa) (p1,p2) = let a = swap isSteep (xa,ya) b = swap isSteep (xb,yb) in swap (fst a > fst b) (a, b) ((x1,y1),(x2,y2)) = (p1,p2) deltax = x2 - x1 deltay = abs (y2 - y1) ystep = if y1 < y2 then 1 else -1
line' :: Point -> Point -> Integer -> Integer -> Integer -> Bool -> Integer -> [Point] line' p1 (x2,_) deltax deltay ystep isSteep = go p1 where go (x1,y1) error = swap isSteep (x1,y1) : rest where rest = if x1 == x2 then [] else go (newX,newY) newError newX = x1 + 1 tempError = error + deltay (newY, newError) = if (2*tempError) >= deltax then (y1+ystep,tempError-deltax) else (y1,tempError)
But now that we got here, you may inline line' and avoid "swap isSteep". I've also changed some names to more pleasant one (for me, at least :). Untested as well:
swap :: Bool -> (a,a) -> (a,a) swap False = id swap True = \(x,y) -> (y,x)
line :: Point -> Point -> [Point] line (xa,ya) (xb,yb) = go (x1,y1) 0 where ((x1,y1),(x2,y2)) = let a = adjust (xa,ya) b = adjust (xb,yb) in swap (fst a > fst b) (a, b) adjust = swap $ abs (yb - ya) > abs (xb - xa) deltax = x2 - x1 deltay = abs (y2 - y1) ystep = if y1 < y2 then 1 else -1
go (x,y) error = let error' = error + deltay (yd,ed) = if 2*tempError >= deltax then (ystep,deltax) else (0,0) in adjust (x,y) : if x == x2 then [] else go (x+1,y+yd) (error' - ed)
HTH, -- Felipe.