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recursionfunctional-programmingsmlsmlnj

How to count the digits of a number recursively in SML

I need to count the digits of a number in a recursive way using Standard ML, assuming that the representation of the number 0 has 1 digit.

fun digitCount 0 = 1
  | digitCount n = 1 + digitCount (n div 10)

It would be easy to do if countDigit(0) was 0, but in the code that I wrote the result will always be added by one.

Solution

  • What about using if then else statement instead of pattern-matching on zero value?

    fun digitCount n =
  if n < 10
  then 1
  else 1 + digitCount (n div 10)

    It's not much more verbose than pattern-matching a can be even written as one-line:

    fun digitCount n = if n < 10 then 1 else 1 + digitCount (n div 10)