Chapter VIII: Appendix: F

Controversial Features of Algol 60

A few features of the language have been subject to more than one interpretation. Fortunately, the vast majority of programs will not involve these ambiguities, but for the few that do it will be necessary to know what decisions the compiler makes. This appendix indicates these decisions for the more controversial areas.

1. Side effects in function designators. The evaluation of primaries
in expressions is not strictly left to right allowing for precedence
rules. In particular, the value of a variable in an expression is
never stored in a temporary simply to preserve its value from change
by the evaluation of a function designator in the expression.
Otherwise, the evaluation does proceed from left to right and
according to precedence rules, including the referencing of formal
parameters and the calculation of the address of subscripted
variables. All function designators are evaluated in Boolean
expressions.

2. Own variables and arrays in procedures. The own quantities local to
the body of a procedure which is called from more than one point in a
program record the history of the procedure as opposed to a history of
each point of reference. In other words, only one copy of the own
quantities is preserved.