Every Dylan statement or expression returns a value. Control constructs and methods generally return the value of the last expression in their body.
if returns a value so it may be used in return position:
format-out("abs(x) = %d", if (x >= 0) x else -x end);
Dylan methods return the value of the last expression in their body to be evaluated. If there is no return value declaration for the generic function then any number of values of type <object> may be returned. This function returns the string “foo”:
define method foo ()
"foo"
end;
Sometimes you write a function for which there is no useful return value. In these cases it is sometimes useful (especially for external APIs) to tell the compiler that no values are returned since it can then give you warnings when callers expect a value. => () is the way to say this:
define method foo () => ()
format-out("foo");
end;