HOMEWORK 3

Notes: 

-- How to hand in the functions you have to write in this homework
   will be explained later on.

-- Before writing a function study its type.

-- You have to use the same names as given for the functions to write.

-- You may use some functions we define in class.

-- You may need to define auxiliary functions. 

Write SML functions to do the following list manipulations

duplicate(L): Duplicates each element of L. For example
duplicate([1,2,3])=[1,1,2,2,3,3].

order(L): Determines if there is any order between the elements
in L and returns 1 if the elements are sorted in non decreasing order,
2 in the case of non increasing order and 3 otherwise. For example
order([1,1,2,3])=1, order([3,2,2,1])=2 and order([1,2,1,3])=3.

flip(L): Flips alternate elements of L. For example
flip([1,2,3,4])=[2,1,4,3].

split(L): splits the list L in half. For example
split([1,2,3,4])=([1,2],[3,4]) and split([1,2,3])= ([1,2],[3]). Note that
the first list must have one more element if the number of elements in
L is not even.

Good work!