space leak

A data structure which grows bigger, or lives longer, than

might be expected. Such unexpected memory use can cause a

program to require more garbage collections or to run out of

heap. Space leaks in functional programs usually result

from excessive laziness. For example, the Haskell function

sum [] = 0

sum (x:xs) = x + sum xs

when applied to a list will build a chain of closures for the

additions and only when it reaches the end of the list will it

perform the additions and free the storage. Another example

is the function

mean l = sum l / length l

The sum function forces the entire list l to be evaluated and

built in the heap. None of it can be garbage collected until

the length function has consumed it.