body

You declare a procedure or function forward when you want to define its header but not its body. This is the case when one procedure or function calls another, which in turn calls the first. This situation is called mutual recursion. The use of forward is necessary in this case because every item must be declared before it can be used. The forward declaration must be followed by a body declaration for the same procedure or function. For details, see forward declarations.

When a procedure or function in a class is declared to be deferred (or simply exported from the class), it can be resolved or overridden afterward by giving its body further down in that class or in descendant classes. The overriding procedure must use the keyword body. See class or "implement by" for examples.

        var token : string
        forward procedure expn (var eValue : real)
            import forward term, var token
        … other declarations appear here …
        body procedure expn
            var nextValue : real
            term (eValue)               % Evaluate t
            loop                        % Evaluate { + t}
                exit when token not= "+"
                get token
                term (nextValue)
                eValue := eValue + nextValue
            end loop
        end expn

The "function" or "procedure" token in the declaration is now optional. In other words the following code fragment is legal

        forward procedure p
        …
        body  p
        …
        end p