grammar/src/when.grm

/**
#### Pattern matching

See [When-expression](control-flow.html#when-expression)
*/

when
  : "when" ("(" expression ")")? "{"
        whenEntry*
    "}"
  ;

// TODO : consider empty after ->
whenEntry
  : whenCondition{","} "->" expression SEMI
  : "else" "->" expression SEMI
  ;

whenCondition
  : expression
  : ("in" | "!in") expression
  : ("is" | "!is") isRHS
  ;