TOPS-20 PASCAL Language Manual - Bitsavers

ISO COMPLIANCE
E.2 IMPLEMENTATION-DEPENDENT FEATURES
These language elements are defined by the ISO 7185 standard as
"possibly differing between processors and not necessarily defined for
any particular processor." Following is a description of how PASCAL-20
treats each of these elements.
1. The order of evaluation of array indices is their lexical
order (t.hat is, left to right).
2. The order of evaluation of members of a set constructor is
their lexical order (that is, left to right).
3. The order of evaluation of the operands of a dyadic operator
(for example, '+') depends on the complexity of each operand.
Both operands are always evaluated (even in Boolean
expressions which could be "short-circuited").
4. The order of evaluation, accessing, and binding of actual
parameters to formal parameters in a procedure or function
call is their lexical order (that is, left to right).
5. The varjable in an assignment statement is accessed after the
evaluation of the expression.
6. The effect of reading a file at the point where a PAGE was
executed when writing the file is to return either a
form-feed character (control-L) or the digit '1', depending
on the status of the file when the PAGE was executed. (See
above for a description of PAGE's actions.)
7. Program parameters which are not file variables have no
defined meaning in PASCAL-20, and cause an error.
E.3 ERROR HANDLING
This section describes how the PASCAL-20 compiler and run-time system
detect violations of level 1 of the standard proposed by the ISO for
the PASCAL language. Errors detected at run time cause a program to
terminate and return appropriate error messages. Errors described
here as "not detected" cause a program to produce unexpected results.
The type of an index value is not assignment compatible with the index
type of an array.
Explanation:
Detected at run time if checking was enabled during
compilation.
The current variant changes while a reference to it exists.
Explanation: Not detected. An example of a reference to a
variant is the passing of the variant to a formal
VAR parameter.
IlIJ'he value of a variable to which a pointer refers (p) is NIL.
Explanation:
Detected if checking was enabled at run time.
The val ue of a va r iable to wh ich a po inter refers (p) is undefined.
Explanation:
Not detected.
E-3