all(x, fn) => bool: returns true if the given function fn evaluates to a
truthy value on all of the items in x. It returns undefined if x is not
enumerable.
any(x, fn) => bool: returns true if the given function fn evaluates to a
truthy value on any of the items in x. It returns undefined if x is not
enumerable.
chunk(x, size) => [object]: returns an array of elements split into groups
the length of size. If x can't be split evenly, the final chunk will be the
remaining elements. It returns undefined if x is not array.
at(x, key) => object: returns an element at the given index (if x is
array) or key (if x is map). It returns undefined if x is not enumerable.
each(x, fn): iterates over elements of x and invokes fn for each
element. fn is invoked with two arguments: key and value. key is an
int index if x is array. key is a string key if x is map. It does not
iterate and returns undefined if x is not enumerable.`
filter(x, fn) => [object]: iterates over elements of x, returning an
array of all elements fn returns truthy for. fn is invoked with two
arguments: key and value. key is an int index if x is array. It returns
undefined if x is not array.
find(x, fn) => object: iterates over elements of x, returning value of
the first element fn returns truthy for. fn is invoked with two
arguments: key and value. key is an int index if x is array. key is
a string key if x is map. It returns undefined if x is not enumerable.
find_key(x, fn) => int/string: iterates over elements of x, returning key
or index of the first element fn returns truthy for. fn is invoked with
two arguments: key and value. key is an int index if x is array.
key is a string key if x is map. It returns undefined if x is not
enumerable.
map(x, fn) => [object]: creates an array of values by running each element
in x through fn. fn is invoked with two arguments: key and value.
key is an int index if x is array. key is a string key if x is map.
It returns undefined if x is not enumerable.
key(k, _) => object: returns the first argument.
value(_, v) => object: returns the second argument.
