Run-length encoding

You are encouraged to solve this task according to the task description, using any language you may know.


Task

Given a string containing uppercase characters (A-Z), compress repeated 'runs' of the same character by storing the length of that run, and provide a function to reverse the compression.

The output can be anything, as long as you can recreate the input with it.



Example

 Input: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
 Output: 12W1B12W3B24W1B14W


Note: the encoding step in the above example is the same as a step of the Look-and-say sequence.




  ( run-length
  = character otherCharacter acc begin end
    .   :?acc
      & 0:?begin
      & @( !arg
         :   ?
             [!begin
             %@?character
             ?
             [?end
             (   (%@:~!character:?otherCharacter) ?
               & !acc !end+-1*!begin !character:?acc
               & !otherCharacter:?character
               & !end:?begin
               & ~`
             | &!acc !end+-1*!begin !character:?acc
             )
         )
      & str$!acc
  )
&   run-length$WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
 