Ticket #3076 (closed bug: wontfix)
Make genericLength tail-recursive so it doesn't overflow stack
A likely use for genericLength is to count lists of more than Int elements. However, the source code is not tail-recursive, making a poor "consumer", so genericLength easily overflows stack.
Here is the source code from 6.10.1:
genericLength :: (Num i) => [b] -> i genericLength  = 0 genericLength (_:l) = 1 + genericLength l
Here is a proposed alternative:
genericLength ∷ (Num i) ⇒ [b] → i genericLength = len 0 where len n  = n len n (_:xt) = len (n+1) xt
In my test application (enumerating the 66,960,965,307 atomic lattices on six atoms) this alternative avoids overflowing the stack.
[This is not the same issue as http://hackage.haskell.org/trac/ghc/ticket/2962]