Primitive syntax

9.1  Unspecified evaluation order

The order in which the subexpressions of an application are evaluated is unspecified, as is the order in which certain subexpressions of some other forms such as letrec are evaluated. While this causes occasional problems, it encourages programmers to write programs that do not depend on a specific evaluation order, and thus may be easier to read. Moreover, it allows the programmer to express that the evaluation order really does not matter for the result. A secondary consideration is that some compilers are able to generate better code if they can choose evaluation order.