\ Split, a Forth program to split a integer (up to 999999999) into seperate digits. by T.Porter 2016
\ Written on FreeBSD using Mecrisp-Stellaris Forth (http://mecrisp.sourceforge.net/) running on a STM32F0 Discovery board, communicating via a Forth Express serial terminal by kfoltman.


\ : split >R BEGIN R> ?DUP 0 > WHILE 10 /MOD >R . cr REPEAT ;


\ Split program explained
: split >R		    \ Save the input on the Return Stack
BEGIN R> ?DUP 0 > WHILE	    \ Fetch from the Return Stack, duplicate because " 0 >" and "/MOD" both use it, then continue while greater than zero after dividing by 10. ?DUP is used instead of DUP to prevent a zero being left on the stack after the program has completed. 
10 /MOD >R . cr		    \ divide by 10 and save the result on the Return Stack, print each remainder on a new line
REPEAT
;


\ Anything added to the return stack during the execution of a word must be removed before the word ends, and the same is true for a loop. So the Return Stack must be tested for 'balance'.


\ In this variation of split, print a label for every Return Stack ADD and REMOVE to visually compare them
: split-labels >R  ." <ADD-1> " cr    \ 999999999 maximum input
BEGIN R> ." <REMOVE> " cr ?DUP 0 > WHILE 
10 /MOD >R ." <ADD-2> " cr  .      
REPEAT
;


\ This time every Return Stack ADD is worth 1 and  REMOVE is worth -1. A total of 0 shows the Return Stack is balanced, so no visual comparison is required.
0 variable rb	    \ 
: split-rbalance
>R rb @ 1+ rb !     
BEGIN
R> rb @ 1- rb !
?DUP 0 > WHILE 
10 /MOD
>R rb @ 1+ rb !
.  cr 
REPEAT
." R balance =  " rb @ .
;


\ *************************** screen pics of all three variants ;) **********************
\ Forth> 123456789 split
\ -> 123456789 split
\ <-  9 
\ <- 8 
\ <- 7 
\ <- 6 
\ <- 5 
\ <- 4 
\ <- 3 
\ <- 2 
\ <- 1 
\ <-  ok.
 

\ Forth> 123456789 split-labels
\ -> 123456789 split-labels
\ <-  <ADD-1> 
\ <- <REMOVE> 
\ <- <ADD-2> 
\ <- 9 <REMOVE> 
\ <- <ADD-2> 
\ <- 8 <REMOVE> 
\ <- <ADD-2> 
\ <- 7 <REMOVE> 
\ <- <ADD-2> 
\ <- 6 <REMOVE> 
\ <- <ADD-2> 
\ <- 5 <REMOVE> 
\ <- <ADD-2> 
\ <- 4 <REMOVE> 
\ <- <ADD-2> 
\ <- 3 <REMOVE> 
\ <- <ADD-2> 
\ <- 2 <REMOVE> 
\ <- <ADD-2> 
\ <- 1 <REMOVE> 
\ <-  ok.


\ Forth> 123456789 split-rbalance
\ -> 123456789 split-rbalance
\ <-  9 
\ <- 8 
\ <- 7 
\ <- 6 
\ <- 5 
\ <- 4 
\ <- 3 
\ <- 2 
\ <- 1 
\ <- R balance =  0  ok. 
\
\
\ **************************************************************************