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.




rle(a) := block(
   [n: slength(a), b: "", c: charat(a, 1), k: 1],
   for i from 2 thru n do
      if cequal(c, charat(a, i)) then k: k + 1 else (b: sconcat(b, k, c), c: charat(a, i), k: 1),
   sconcat(b, k, c)
)$
 
rle("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW");
"12W1B12W3B24W1B14W"