factorial function input int, output real?

1
votes

This is absolutely driving me nuts. The supposed simplest thing I can imagine and I can't do it.

I just want to computer factorial inputting an int and output a real.

I've tried to coerce in numerous way.

fun factorial 0 = 1 |
    factorial n = n * factorial(n-1);
3
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3 Answers

3
votes

To convert an int to a real, you use Real.fromInt. If you want to return reals, you should also return 1.0 instead of 1 as the base case. So your code becomes:

fun factorial 0 = 1.0
  | factorial n = (Real.fromInt n) * factorial(n-1);
1
votes

Mathematically, n! = (n-1)! * n . Unless i'm misunderstanding things (which is possible; i don't know ML), your function will always return 1 because it's never multiplying by n.

fun factorial 0 = 1 |
    factorial n = n * factorial(n-1);

I don't know how you return a real rather than an int, or whether this code even does it, but at the very least it should give you a correct value.