Henning Thielemann wrote:
On Thu, 8 May 2008, Madoc wrote:
minValue = 0::Int maxValue = 1000::Int
normalize a | a < minValue = minValue | a > maxValue = maxValue | otherwise = a
normalize' = min maxValue . max minValue
There is a curiosity here. The functions normalize and normalize' are extensionally equal only because minValue <= maxValue, but intensionally different. The intensional equivalent is to reverse order of composition: normalize'' = max minValue . min maxValue which remains equal to to normalize whatever the values of minValue and maxValue. That the order of composition (or of guarded expressions) matters conditionally base on its parameters is reason enough for the original poster to decide what the "right answer" should be if maxValue < minValue. These corner cases are often where future bugs lie dormant. My choice would be: normalize''' = max trueMin . min trueMax where trueMin = min minValue maxValue trueMax = max minValue maxValue Now the function makes no assumptions about external values. This is no less efficient than before, since trueMin and trueMax are CAFs evaluated only once.