RosettaCodeData/Task/Run-length-encoding/Picat/run-length-encoding-1.picat

rle(S) = RLE =>
  RLE = "",
  Char = S[1],
  I = 2,
  Count = 1,
  while (I <= S.len)
    if Char == S[I] then
      Count := Count + 1
    else
      RLE := RLE ++ Count.to_string() ++ Char.to_string(),
      Count := 1,
      Char := S[I]
    end,
    I := I + 1
  end,
  RLE := RLE ++ Count.to_string() ++ Char.to_string().