collapseos/blk/042

Flow

Note about flow words: flow words can only be used in
definitions. In the INTERPRET loop, they don't have the desired
effect because each word from the input stream is executed
immediately. In this context, branching doesn't work.

f IF A ELSE B THEN: if f is true, execute A, if false, execute
B. ELSE is optional.
BEGIN .. f UNTIL: if f is false, branch to BEGIN.
BEGIN .. AGAIN: Always branch to BEGIN.
x y DO .. LOOP: LOOP increments y. if y != x, branch to DO.
x CASE y OF A ENDOF z OF B ENDOF C ENDCASE: If x == y, execute
A, if x == z, execute B. Otherwise, execute C.

                                                        (cont.)