A Boolean flag is cell-sized. A cell with all bits clear represents the
flag false and a flag with all bits set represents the flag
true. Words that check a flag (for example, IF) will treat
a cell that has any bit set as true.
true ( – f ) core-ext “true”
Constant – f is a cell with all bits set.
false ( – f ) core-ext “false”
Constant – f is a cell with all bits clear.
on ( a-addr – ) gforth-0.2 “on”
Set the (value of the) variable at a-addr to true.
off ( a-addr – ) gforth-0.2 “off”
Set the (value of the) variable at a-addr to false.
select ( u1 u2 f – u ) gforth-1.0 “select”
If f is false, u is u2, otherwise u1.