hi , I am stuck in the following problem. I am maintaining a list of tuples of the form ([Char],Int,Int, Int,Int) . The purpose of maintaining the tuples is that the program reads from a file line by line , Matches the contents with the first element of the tuple and updates the tuple respectively. The precise function I am using is as follows tupup::Bool->[Char]->Int->Int->Int->Int->Char->([Char],Int,Int,Int,Int) tupup val elf els elr ell elx ys= if val then case ys of 'A' -> (elf, els+1,elr,ell,elx) 'G' -> (elf,els, elr +1,ell,elx) 'C' -> (elf,els,elr, ell +1,elx) 'T' -> (elf,els,elr,ell, elx +1) else (elf,els,elr,ell,elx) uptable::[[Char]]->[([Char],Int,Int,Int,Int)]->[([Char],Int,Int,Int,Int)] uptable (xf:xs) main_array = map (\(x,y,z,r,t)-> tupup (x==xf) x y z r t (secvalue xs) ) main_array It gives the error ERROR - Control stack overflow. I assume it is because of the lazy evaluation . Is there a way to enforce strict evaluation only for the function tupup. Thanks, Navin