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operator and operand don't agree error in this simple function

Consider this definition:

fun abs(x:int):int = (x*x)/(~x);

which should return the absolute value of the input. But when the function is called, I get this error: 

Error: operator and operand don't agree [tycon mismatch]
  operator domain: real * real
  operand:         int * int
  in expression:
    x * x / ~ x

What am I doing wrong? Didn't I use :intcorrectly?

Thanks

Solution

  • In SML, / is division on reals. For integers, you need to use div.

    > fun abs x = x*x div ~x;
val abs = fn : int -> int