When multiplying
x and
y the answer is
y*x,
unless
0 or
1 is involved:
: TIMES ( x y -- y*x | x | y )
OVER 0= OVER 1 = OR IF DROP EXIT THEN
OVER 1 = OVER 0= OR IF NIP EXIT THEN
* ;
However, we can simplify this:
: TIMES ( x y -- y*x ) * ;
This illustrates that obvious exceptions not necessarily need special treatment.
Of course, it will not always be as simple as
TIMES.
The following program removes exceptions
( **) by transforming them
to regular actions.
Because there are no conditional branches anywhere,
the program flow is very easy to follow.
The only concession is the
UNTIL at the end of
PLAY.
Forth file: ec206.frt
\ Shift game (Albert Nijhof)
\ The player shifts the blocks to their correct position.
FORTH DEFINITIONS DECIMAL
: CHAR-ARRAY ( amount -- ) \ Defining word
CREATE 255 UMIN \ Max. length? ( **)
DUP C, 1+ ALLOT ALIGN
DOES> ( index -- address )
COUNT ROT UMIN + ; \ Range? ( **)
#16 CHAR-ARRAY board \ 15 chars plus an empty space
0 VALUE SPOT \ Position of empty space
: FINAL ( -- )
S" VIJGEBLAD*FORTH "
DUP 1- TO SPOT
0 BOARD SWAP MOVE ;
