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.


import scala.io.Source
import java.io.PrintStream
 
def process(s: Source, p: PrintStream, w: Int = 0): Unit = if (s.hasNext) s.next match {
  case '.' => p append '.'
  case c if !Character.isAlphabetic(c) => p append c; reverse(s, p, w + 1)
  case c => p append c; process(s, p, w)
}
 
def reverse(s: Source, p: PrintStream, w: Int = 0, x: Char = '.'): Char = s.next match {
  case c if !Character.isAlphabetic(c) => p append x; c
  case c => val n = reverse(s, p, w, c);
    if (x == '.') {p append n; process(s, p, w + 1)} else p append x; n
}
 
process(Source.fromString("what,is,the;meaning,of:life."), System.out); println
process(Source.fromString("we,are;not,in,kansas;any,more."), System.out); println