Conditional block

A cond expression allows branching based on conditions.

Syntax

cond_expression
  = "cond" "{" (cond_branch ",")+ cond_else_branch ","? "}"

cond_branch
  = expression "->" branch_body

cond_else_branch
  = "else" "->" branch_body

branch_body
  = expression
  / "{" (expression ";")+ "}"

Example

cond {
  age < 18 -> "minor",
  age < 60 -> "adult",
  else -> "senior",
};

Semantics

Every conditional expression MUST return a boolean (true or false). If they don't, an exception MUST be thrown, the value of that exception is defined by the implementation.

If a conditional expression throws an exception, that exception MUST NOT be ignored, and MUST bubble up.

The body of the branch with the first conditional expression that returns true MUST be evaluated. The cond expression MUST evaluate to the value this branch evaluates to.

The conditional expressions following one that returned true MUST NOT be evaluated (this is short-circuiting).

If no conditional expression returns true, the default else branch MUST be evaluated.

Each branch MUST create a new scope.