Here's a simple snippet to demonstrate the usage of the for do done looping construct. We'll also make use of the random number generator (the one in the System namespace which is essentially, NOT random, but is suitable for our demonstration). Note that this construct looks like it is functional style until we hit that "printf" statement which creates the output to console side-effect.

Basic Case

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let aPRNG = new System.Random();;
for someLoopVariableThatDoesntMatter = 0 to 99
do
   printf "%i\n" (aPRNG.Next(1, 100))
done;
;;

Basic Case with a function definition

This could also be written as follows with the "Next" method on the System.Random object as a function:

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let bPRNG = new System.Random();;
let GetRan a b = bPRNG.Next(a, b);;
for someLoopVariableThatDoesntMatter = 0 to 99
do
   printf "%i\n" (GetRan 1 100)
done;
;;

In the second example, it is important to consider that the "GetRan" function is bound to the Next method of bPRNG, a System.Random object, while the arguments remain free (as they should).