Everything is a value

Every Dylan statement or expression returns a value. Functions and control constructs like select and for return the values of the last expression in their body.

if returns a value so it may be used in return position:

let abs = if (x >= 0) x else -x end;

Dylan functions return the values of the last expression in their body to be evaluated. This function returns either “foo” or “bar”:

define function foobar ()
  if (odd?(random(100)))
    "foo"
  else
    "bar"
  end
end;

If there is no return value declaration for a function then any number of values of any type can be returned. Use => (...decls...) to declare return values. This function returns no values:

define function foo () => ()
  format-out("foo");
end;

This function returns an integer and a string:

define function bar () => (size :: <integer>, description :: <string>)
  values(42, "the meaning of everything")
end;