Q: Why does the Forth word if require a then?
A: Unlike languages such as C, Forth requires an if to be followed
by an else followed by a then. In the case without an
else, the then must still follow an if.
Since any character, number, or symbol can be a Forth word, you cannot use a pair
of parentheses to encase the code following an if or else.
The left paren character, (, is a Forth word. It tells the Forth interpreter to stop
interpreting input and collect all text, as comments, until a right paren character, ),
is encountered. A more rigorous definition for the if word is:
The then is the delimiter to the true or false function, since the true
action follows the if statement and the false action follows
the else statement. Other non-conditional code can follow the "if
then" clause before the end of the definition.
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