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When a word is compiled, it behaves differently from being interpreted.
1 2 + . : foo + ;
These two behaviours are known as compilation and interpretation
semantics. For normal words (e.g.,
+), the compilation semantics
is to append the interpretation semantics to the currently defined word
foo in the example above). I.e., when
foo is executed
later, the interpretation semantics of
+ (i.e., adding two
numbers) will be performed.
However, there are words with non-default compilation semantics, e.g.,
the control-flow words like
if. You can use
change the compilation semantics of the last defined word to be equal to
the interpretation semantics:
: [FOO] ( -- ) 5 . ; immediate [FOO] : bar ( -- ) [FOO] ; bar see bar
Two conventions to mark words with non-default compilation semantics are names with brackets (more frequently used) and to write them all in upper case (less frequently used).
In Gforth (and many other systems) you can also remove the
interpretation semantics with
compile-only (the compilation
semantics is derived from the original interpretation semantics):
: flip ( -- ) 6 . ; compile-only \ but not immediate flip : flop ( -- ) flip ; flop
In this example the interpretation semantics of
flop is equal to
the original interpretation semantics of
The text interpreter has two states: in interpret state, it performs the interpretation semantics of words it encounters; in compile state, it performs the compilation semantics of these words.
Among other things,
: switches into compile state, and
switches back to interpret state. They contain the factors
(switch to compile state) and
[ (switch to interpret state), that
do nothing but switch the state.
: xxx ( -- ) [ 5 . ] ; xxx see xxx
These brackets are also the source of the naming convention mentioned above.
Reference: Interpretation and Compilation Semantics.