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.


(define (odd)
  (let ((c (read-char)))
    (if (char-alphabetic? c)
      (let ((r (odd)))
	(write-char c)
	r)
      (lambda () (write-char c) (char=? c #\.)))))
 
(define (even)
  (let ((c (read-char)))
    (write-char c)
    (if (char-alphabetic? c)
      (even)
      (char=? c #\.))))
 
(let loop ((i #f))
  (if (if i ((odd)) (even))
    (exit)
    (loop (not i))))