On Mon, 16 Apr 2007, Gaetano Caruana wrote:
Hi all. I am new to this list ;) Today I have encountered something new that has never happened to me in the past 6 months that I have been using ghci and Haskell.
I wrote this function:
type Line = (Point,Point) type Point = (Float,Float)
circleLineIntersection :: Float -> Float -> Float -> Line -> Maybe [Point] circleLineIntersection h k r ((x1,y1),(x2,y2)) = do
no 'do' is needed here
let perpdist = calcPerpDist (h,k) ((x1,y1),(x2,y2)) noSolution = perpdist > r oneSolution = perpdist == r twoSolutions = perpdist < r
case compare perpdist r of GT -> EQ -> LT -> ...
in do if noSolution then Nothing else let dx = x2 - x1 dy = y2 - y1 dr = sqrt (dx * dx + dy * dy)
Why computing sqrt if you only use dr*dr?
bigD = x1 * y2 - x2 * y1 x1 = ( bigD * dy + sign (dy) * dx * sqrt( r * r * dr * dr - bigD * bigD ) ) / (dr * dr) y1 = - bigD * dx + abs(dy) * sqrt( r * r * dr * dr - bigD * bigD ) / (dr * dr) x2 = ( bigD * dy - sign (dy) * dx * sqrt( r * r * dr * dr - bigD * bigD ) ) / (dr * dr) y2 = - bigD * dx - abs(dy) * sqrt( r * r * dr * dr - bigD * bigD ) / (dr * dr)
ghci -Wall should have warned you, that y2 shadows function argument y2. Thus you programmed an infinite cycle.