Folks I am new in this forum, so apologies if this has been asked before. If this is the case, please point me to the direction of the answer and I won't bother you again! Also, could you make sure you CC your answers to me? I am not sure how long it takes for my subscription to be activated and I don't want to miss out on the action :-) The Problem I have defined this function to calculate the Fibonacci numbers: all_fib :: [Float] all_fib = 1:(1:(add_fib all_fib)) where add_fib (x:y:rs) = (x + y):(add_fib (y:rs)) Which seems to work: Main> take 20 all_fib [1.0,1.0,2.0,3.0,5.0,8.0,13.0,21.0,34.0,55.0,89.0,144.0,233.0,377.0, 610.0,987.0,1597.0,2584.0,4181.0,6765.0] However, when I tried Main> filter even (take 20 all_fib) ERROR - Illegal Haskell 98 class constraint in inferred type *** Expression : filter even (take 20 all_fib) *** Type : Integral Float => [Float] What is going on here? Thanks in advance for any help/hint. -- Wamberto Vasconcelos, PhD wvasconcelos@acm.org Department of Computing Science http://www.csd.abdn.ac.uk/~wvasconc University of Aberdeen, Aberdeen AB24 3UE, Scotland, UK Phone +44 (0)1224 272283 Fax +44 (0)1224 273422