( The Towers Of Hanoi                                 )
( FORTH                                               )
( Copyright 1998 Amit Singh. All Rights Reserved. )
( http://hanoi.kernelthread.com                       )
(                                                     )
( Tested under GNU Forth 0.3.0, PFE 0.9.14            )

( Use "gforth <thisfile> -e 'n HANOI bye'" to run     )
( hanoi with n disks. Alternatively, load everything  )
( and use the HANOI word from within the interpreter. )

: MOVEIT ." move " . ." --> " . CR ;     ( to from -- )

: DOHANOI                        ( to from using n -- )
                                  ( T3 <- T1 using T2 )
  DUP 0 >                         ( more disks ?      )
  IF
    1 -                           ( n <- n - 1        )
    2OVER 2OVER                   ( clone data stack  )
    >r >r >r >r                   ( save it to rstack )
    1 ROLL 2 ROLL 3 ROLL 3 ROLL   ( using from to n-1 )
    RECURSE                       ( T2 <- T1 using T3 )
    2r@ SWAP MOVEIT               ( to from           )
    2DROP 2DROP                   ( empty the stack   )
    2r> 2r>                       ( from to n-1 using )
    SWAP                          ( from to using n-1 )
    3 ROLL                        ( to using n-1 from )
    SWAP                          ( to using from n-1 )
    RECURSE                       ( T3 <- T2 using T1 )
THEN ;

: HANOI ( n -- )                  ( prepare arguments )
3 1 2 3 ROLL DOHANOI 2DROP 2DROP ;