Introduction to programming using SML exercise 1.3

Question

I am currently working through the Introduction to programming using SML book released back in 1999. I would like your help on how to declare a recursive function for exercise 1.3, which I have been stuck on for some time now.

1.3: Declare a recursive function f: int -> int, where f(ᶯ) = 1 + 2 + ... + (ᶯ - 1) + ᶯ for ᶯ ≥ 0

Hint: Use two clauses with 0 and ᶯ as argument patterns. State the recursion formula corresponding to the declaration.

If anyone can provide some guidance on this that would be great.

I have not written any code for this function yet because I am trying to understand what it does. — Kirk Friend
– Kirk Friend, Commented Jun 17, 2014 at 13:22

molbdnilo · Accepted Answer · 2014-06-17 13:17:08Z

2

More literal hint:

The solution is supposed to look like this:

fun sum 0 = ... something ...
  | sum n = ... something else ...

You'll need to figure out

What is sum 0?
What information do you need in order to be able to calculate sum n?

If you're stuck, write down the calculation of f(1), f(2), f(3), and f(4) on a piece of paper and see if you can spot a pattern.

answered Jun 17, 2014 at 13:17

molbdnilo

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1 Comment

Kirk Friend Over a year ago

I think this may have helped me. Here is what I have: fun f 0 = 0 | f n = n + f(n-1);

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