6.11.4 The choose Statement

The choose statement chooses an element of a list. Its format is:

     choose $var in expr;

For every element in the list expr a rule path is created; in this rule path the element is stored in the variable $var. Thus the number of rule paths can multiply. If, for example, expr has the value <A, B, C>, the currently processed rule path has three continuations: In the first one $var has the value A, in the second one it has the value B and in the third one it has the value C. The three paths behave independently from now on.

The choose statement can also be used for records. In that case, the variable $var gets a different attribute name of the record expr in each path.

The choose statement also works for numbers:

• If expr is a positive number n, the variable $var is assigned the numbers 1, 2, ..., n, respectively, in each path.
• If expr is a negative number -n, the variable $var is assigned the numbers -1, -2, ..., -n, respectively, in each path.