Fuzion • Idioms • Idiom # 173: Format a number with grouped thousands

Idiom # 173: Format a number with grouped thousands

String based approach

Code

Runnable Example

ex173 is
  format(x T : integer) String =>

      str:= x.as_string

      len := str.byte_length

      first :=
          if x < T.zero && len%3 = 1 then 4      # avoid separator right after minus
          else if len%3 > 0          then len%3  # determine size of first group
          else                            3

      groups(start i32, str0 String) String =>
          if start > (str0.byte_length - 3)
          then ""
          else "," + (str0.substring start (start + 3)) + groups (start + 3) str0

      (str.substring (0) (first)) + (groups first str)


  numbers := [1, 42, 123, 1234, 12345, 123456, 1234567, 12345678, 123456789]

  for n in numbers
  do say "$n -> {format n}"

  for n in numbers
  do n_neg := n*(-1); say "$n_neg -> {format n_neg}"

  a := int i64.max
  say (format a*a)

What are effects?

Numeric way

Runnable Example for i32

last changed: 2026-02-20

next: NYI: Idiom # 174: Make HTTP POST request