[Haskell-cafe] Writing a pnm file

Hi, Now that I've understood how to generate raster points of a line in Haskell - the next thing I want to do is generate a pnm file with it. I've done it in perl as of now. In perl, I can have a scalar variable $x contain a string of 256*256*3 bytes (for 24-bit 256x256 image) and set pixels using substr on LHS. I was wondering how I could do something similar in Haskell? sub setPixel{ my($x,$y,$red,$green,$blue)=@_; my$pixel=pack "CCC",$red,$green,$blue; my$offset=$WIDTH*$y*3 + $x*3; substr($image,$offset,3) = $pixel; } Regards, Kashyap