2.2.2 Method Bodies

The syntax of the body of a method, closure, or parenthetical subexpression is as follows:

body	::=	{stmt} result
	|	empty	return void
result	::=	normal_return	return an expression
	|	non_local_rtn	return from the lexically-enclosing method
normal_return	::=	decl_block [";"]	return void
	|	assignment [";"]	return void
	|	expr [";"]	return result of expression
non_local_rtn	::=	"^" [";"]	do a non-local return, returning void
	|	"^" expr [";"]	do a non-local return, returning a result

(The syntax and semantics of statements and expressions is described in section 2.5.)

When invoked, a method evaluates its statements in a new environment containing bindings for the method's formal parameters and nested in the method's lexically-enclosing environment. (The interactions among nested scopes, method lookup, and other language features is described in more detail in section 2.7.7.)

The result of the message invoking the method is the result of the last statement in the method's body. If the method's body is empty, then the method returns the special void value. Alternatively, a method returns void if the last statement is a declaration block, an assignment statement, or an expression that itself returns void. The void value is used to indicate that the method returns no useful result. The system ensures that void is not accidentally used in later computation by reporting an error (statically in the presence of type checking) if void is passed as an argument to a message.

When a closure's eval method is invoked, evaluation proceeds much like the evaluation of any other method. One difference is that a closure eval method may force a non-local return by prefixing the result expression with the ^ symbol; if the result expression is omitted, then void is returned non-locally. A non-local return returns to the caller of the closest lexically-enclosing non-closure method rather than to the caller of the eval method, just like a non-local return in Smalltalk-80[3] [Goldberg & Robson 83] and Self and similar to a return statement in C. The language currently prohibits invoking a non-local return after the lexically-enclosing scope of a closure has returned; first-class continuations are not supported.