head-strict

theory A head-strict function will not necessarily evaluate

every cons cell of its (list) argument, but whenever it does

evaluate a cons cell it will also evaluate the element in the

head of that cell. An example of a head-strict function is

beforeZero :: [Int] -@# [Int]

beforeZero [] = []

beforeZero (0:xs) = []

beforeZero (x:xs) = x : beforeZero xs

which returns a list up to the first zero.

This pattern of evaluation is important because it is common

in functions which operate on a list of inputs.

See also tail-strict, hyperstrict.

(1995-05-11)