Write two functions that each take a function and a list. One of them will
return the list of items for which the passed in function is true, and the
other will return the items for which it is false.

For example, given the collection of numbers:

• 1, 2, 3, 4, 5

And the predicate:

• is the number even?

Then your keep operation should produce:

• 2, 4

While your discard operation should produce:

• 1, 3, 5

Note that the union of keep and discard is all the elements.

The functions may be called keep and discard, or they may need different
names in order to not clash with existing functions or concepts in your
language.

Restrictions

Keep your hands off that filter/reject/whatchamacallit functionality
provided by your standard library! Solve this one yourself using other
basic tools instead.