Keeping the answers ordering on "oldest".

Empirical orders of growth, please!

primes = [2..] \ [[p², p²+p ..] | p <- primes]

((g<=<f)=<<) = (g=<<).(f=<<) = join.(g<$>).join.(f<$>)

Monads as generalized function application

condU:(g ~~>! h) f x = case g x of [] -> f x; (y:_) -> h y
apply (FUNARG lambda env) xs a = apply lambda xs env
hammingSlice hi w = (c, sortBy (compare `on` fst) b) where
1:foldr (\n s->fix (merge s . (n:) . map (n*))) [] [2,3,5]
ordfactors = foldr g [1] . reverse . primePowers where

in a declarative language,
length(a) == 0 is the same as null(a),
and [y | x <- [1..], y <- []] is just [].

What's in a powerset? A set's subsets...
(define (call/cc& proc& k) (proc& k k))
(define (list . xs) xs)

How Monads are considered Pure?
Monads are EDSLs are Nested Loops are Trees:
do { [1,2,3] ; [4,5] } => do { x <- [1,2,3] ; do { y <- [4,5] ; return y }} => for x from [1,2,3] { for y from [4,5] { yield y }} => [ 4,5, 4,5, 4,5 ]

Is your ( programming ) language ( high-level ) enough?