F# Programming:

Write an F# program lengthsort to sort a list of lists according the lengths of the element lists such that short lists first, longer lists later.

> lengthsort [[2;3];[1;2;3;4];[1;2;4;5;6];[2;3;4];[3]];; val it : int list list =

[[3]; [2; 3]; [2; 3; 4]; [1; 2; 3; 4]; [1; 2; 4; 5; 6]]

Hint: Use List.map to construct a tuple list from the given list such that the first element is the length of the element list, e.g [[2;3];[1;2;3;4];[1;2;4;5;6];[2;3;4];[3]] becomes [(2,[2;3]);(4,[1;2;3;4]);(5,[1;2;4;5;6]);(3,[2;3;4]);(1,[3])]. Write a function to sort the list based on the 1st element of the tuple, and then drop the 1st element in the tuples to obtain the final result.