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Boolean Flags

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       ``on''
Set the (value of the) variable at a-addr to true. 
off       a-addr --         gforth       ``off''
Set the (value of the) variable at a-addr to false.