VDM-10 Language Manual

Appendix C
Operator Precedence
The precedence ordering for operators in the concrete syntax is defined using a two-level approach:
operators are divided into families, and an upper-level precedence ordering, >, is given for the
families, such that if families F 1 and F 2 satisfy
F 1 > F 2
then every operator in the family F 1 is of a higher precedence than every operator in the family F 2 .
The relative precedences of the operators within families is determined by considering type
information, and this is used to resolve ambiguity. The type constructors are treated separately,
and are not placed in a precedence ordering with the other operators.
There are six families of operators, namely Combinators, Applicators, Evaluators, Relations,
Connectives and Constructors:
Combinators: Operations that allow function and mapping values to be combined, and function,
mapping and numeric values to be iterated.
Applicators: Function application, field selection, sequence indexing, etc.
Evaluators: Operators that are non-predicates.
Relations: Operators that are relations.
Connectives: The logical connectives.
Constructors: Operators that are used, implicitly or explicitly, in the construction of expressions;
e.g. if-then-elseif-else, ‘|->’, ‘. . . ’, etc.
The precedence ordering on the families is:
combinators > applicators > evaluators > relations > connectives > constructors
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