I should have been more careful with my terminology: I'm talking about evaluation order, not execution order. In the expression "f(g(x))", the procedure named "g" is executed before the procedure named "f", but the expression "g" may or may not be evaluated before the expression "f". (Scheme doesn't specify evaluation order for an application expression; I don't know if Perl does. Actually I don't even know if an operator in Perl can be an expression or must be a name.)