else expression

The grounding “else” expression is a fairly new construct in programming languages; syntactically, it is similar to the “else” branch of a ternary expression:

a : b

The expression yields the result of the expression a. If the expression a arcs, then the expression yields the result of the expression b.

It is a compile-time error if expression a does not short-circuit. The expression short-circuits iff expression b short-circuits.

Definite assignment rules:

• The VAS before a is the VAS before the expression.
• The VAS before b is the join of the VAS from each short-circuiting point in a.
• The VAS after the expression is the join of the VAS after a and the VAS after b.

Note that the “else” operator groups to the right, which is different from most other binary operators:

    ElseExpression:
        TernaryExpression
        TernaryExpression : Expression

That means that a : b : c is treated the same as a : (b : c).