Editing Forth (programming language) (section)

==== Compilation state and interpretation state ====
The word <code>:</code> (colon) parses a name as a parameter, creates a dictionary entry (a ''colon definition'') and enters compilation state. The interpreter continues to read space-delimited words from the user input device. If a word is found, the interpreter executes the ''compilation semantics'' associated with the word, instead of the ''interpretation semantics''. The default compilation semantics of a word are to append its interpretation semantics to the current definition.<ref name="compiler" />

The word <code>;</code> (semi-colon) finishes the current definition and returns to interpretation state. It is an example of a word whose compilation semantics differ from the default. The interpretation semantics of <code>;</code> (semi-colon), most control flow words, and several other words are undefined in {{Not a typo|ANS}} <!-- not a misspelling --> Forth, meaning that they must only be used inside of definitions and not on the interactive command line.<ref name="compiler" />

The interpreter state can be changed manually with the words <code><nowiki>[</nowiki></code> (left-bracket) and <code><nowiki>]</nowiki></code> (right-bracket) which enter interpretation state or compilation state, respectively. These words can be used with the word <code>LITERAL</code> to calculate a value during a compilation and to insert the calculated value into the current colon definition. <code>LITERAL</code> has the compilation semantics to take an object from the data stack and to append semantics to the current colon definition to place that object on the data stack.

In {{Not a typo|ANS}} <!-- not a misspelling --> Forth, the current state of the interpreter can be read from the [[flag (programming)|flag]] <code>STATE</code> which contains the value true when in compilation state and false otherwise. This allows the implementation of so-called ''state-smart words'' with behavior that changes according to the current state of the interpreter.