F# and all ML derivatives are an aberration because they use juxtaposition to denote function calls. That eliminates a lot of parens but personally I find the result less readable.

But compare to, say, C where no one complains about the parens:

    int fact(int n) {
      if (n==0) {
        return 1
      } else {
        return n*fact(n-1);
      }
    }

That's six pairs of parens. The only reason it's not more is because some function calls in C are disguised as operators, and those just happen to be the functions that factorial uses. If we wanted a semantically equivalent function that handled bignums you'd have to write:

    bignum fact(bignum n) {
      if (bignum_is_zero(n)) {
        return n;
      else {
        return bignum_multiply(n, fact(bignum_subtract_1(n)));
      }
    }

Now you've got nine parens. But still no one complains about C because of that.