Re: [Haskell-cafe] Need feedback on my Haskell code

28 Jul 2009

      Thanks Neil,
That helped. Now the code looks better - I still feel a little bad about the way I repeat calls to line' though - I was thinking of using a partially applied function with (newX,newY) as the last parameter - but that'll make the code less readable.

line :: Point -> Point -> [Point]
line (xa,ya) (xb,yb) = line' (x1,y1) (x2,y2) deltax deltay ystep isSteep 0
  where
    isSteep = abs (yb - ya) > abs (xb - xa)
    (xa',ya',xb',yb') = if isSteep
      then (ya,xa,yb,xb)
      else (xa,ya,xb,yb)
    (x1,y1,x2,y2) = if xa' > xb'
      then (xb',yb',xa',ya')
      else (xa',ya',xb',yb')
    deltax = x2 - x1
    deltay = abs (y2 - y1)
    ystep = if y1 < y2 then 1 else -1

line' (x1, y1) (x2, y2) deltax deltay ystep isSteep error
  | x1 == x2 = if isSteep then [(y1, x1)] else [(x1, y1)]
  | isSteep =
    (y1, x1) :
      line' (newX, newY) (x2, y2) deltax deltay ystep isSteep newError
  | otherwise =
    (x1, y1) :
      line' (newX, newY) (x2, y2) deltax deltay ystep isSteep newError
  where newX = x1 + 1
        tempError = error + deltay
        (newY, newError)
          = if (2 * tempError) >= deltax then
              (y1 + ystep, tempError - deltax) else (y1, tempError)

Regards,
Kashyap

________________________________
From: Neil Mitchell <ndmitchell@gmail.com>
To: CK Kashyap <ck_kashyap@yahoo.com>
Cc: haskell-cafe@haskell.org
Sent: Tuesday, July 28, 2009 6:44:58 PM
Subject: Re: [Haskell-cafe] Need feedback on my Haskell code

Hi Kashyap,

My first suggestion would be to run HLint over the code
(http://community.haskell.org/~ndm/hlint) - that will spot a few easy
simplifications.

Thanks

Neil

On Tue, Jul 28, 2009 at 2:04 PM, CK Kashyap<ck_kashyap@yahoo.com> wrote:
...
Hi Everyone,
I managed to write up the line drawing function using the following links -
http://www.cs.helsinki.fi/group/goa/mallinnus/lines/bresenh.html
http://rosettacode.org/wiki/Bresenham%27s_line_algorithm#Haskell
line :: Point -> Point -> [Point]
line (xa,ya) (xb,yb) = line' (x1,y1) (x2,y2) deltax deltay ystep isSteep 0
  where
    isSteep = abs (yb - ya) > abs (xb - xa)
    (xa',ya',xb',yb') = if isSteep
      then (ya,xa,yb,xb)
      else (xa,ya,xb,yb)
    (x1,y1,x2,y2) = if xa' > xb'
      then (xb',yb',xa',ya')
      else (xa',ya',xb',yb')
    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' (x1,y1) (x2,y2) deltax deltay ystep isSteep error =
  if x1 == x2
  then if isSteep then [(y1,x1)] else [(x1,y1)]
  else
    if isSteep
      then [(y1,x1)] ++ line' (newX,newY) (x2,y2) deltax deltay ystep
isSteep newError
      else [(x1,y1)] ++ line' (newX,newY) (x2,y2) deltax deltay ystep
isSteep newError
        where
          newX = x1 + 1
          tempError = error + deltay
          (newY, newError) = if (2*tempError) >= deltax then
(y1+ystep,tempError-deltax) else (y1,tempError)
Can someone please provide feedback on this? In terms of, how do I get more
Haskell'ism into it.
Regards,
Kashyap
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