flat : 'a list list -> 'a list
SYNOPSIS
Flattens a list of lists into one long list.
DESCRIPTION
flat [l1;...;ln]
returns
(l1 @ ... @ ln)
where each li is a list and
@
is list concatenation.
FAILURE CONDITIONS
Never fails.
EXAMPLE
# flat [[1;2];[3;4;5];[6]];; val it : int list = [1; 2; 3; 4; 5; 6]