Question

Consider this:

ruleset = [rule0, rule1, rule2, rule3, rule4, rule5]

where rule0, rule1, etc. are boolean functions that take one argument. What is the cleanest way to find if all elements of a particular list satisfy all the rules in the ruleset?

Obviously, a loop would work, but Haskell folks always seem to have clever one-liners for these types of problems.

The all function seems appropriate (eg. all (== check_one_element) ruleset) or nested maps. Also, map ($ anElement) ruleset is roughly what I want, but for all elements.

I’m a novice at Haskell and the many ways one could approach this problem are overwhelming.

Answer 1

If you require all the functions to be true for each argument, then it’s just

and (ruleset <*> list)

(You’ll need to import Control.Applicative to use <*>.)

Explanation:

When <*> is given a pair of lists, it applies each function from the list on the left to each argument from the list on the right, and gives back a list containing all the results.