Task

Write a program that solves the odd word problem with the restrictions given below.



Description

You are promised an input stream consisting of English letters and punctuations.

It is guaranteed that:

 the words (sequence of consecutive letters) are delimited by one and only one punctuation,
 the stream will begin with a word,
 the words will be at least one letter long,   and 
 a full stop (a period, [.]) appears after, and only after, the last word.


Example

A stream with six words:

 what,is,the;meaning,of:life. 


The task is to reverse the letters in every other word while leaving punctuations intact, producing:

 what,si,the;gninaem,of:efil. 
while observing the following restrictions:

 Only I/O allowed is reading or writing one character at a time, which means: no reading in a string, no peeking ahead, no pushing characters back into the stream, and no storing characters in a global variable for later use;
 You are not to explicitly save characters in a collection data structure, such as arrays, strings, hash tables, etc, for later reversal;
 You are allowed to use recursions, closures, continuations, threads, co-routines, etc., even if their use implies the storage of multiple characters.


Test cases

Work on both the   "life"   example given above, and also the text:

 we,are;not,in,kansas;any,more.


putch=: 4 :0                 NB. coroutine verb
  outch y
  return x
)
 
isletter=: toupper ~: tolower
 
do_char=: 3 :0                 NB. coroutine verb
  ch=. getch''
  if. isletter ch do.
    if. odd do.
      putch&ch yield do_char '' return.
    end.
  else.
    odd=: -. odd
  end.
  return ch
)
 
evenodd=: 3 :0
  clear_outstream begin_instream y
  odd=: 0
  whilst. '.'~:char do.
    outch char=. do_char coroutine ''
  end.
)