opensLexicalFrame function

bool opensLexicalFrame(SAstNode node)

Does node open a new runtime Environment frame?

This is the shared scope-frame predicate (plan_3 §4.4, risk R1): the single decision the resolver and the interpreter must agree on. It is deliberately over-approximating — it may return true for a construct the interpreter happens not to wrap in its own frame. Over-approximation is safe for the depth-0 resolver: modelling an extra frame only ever raises a computed depth (suppressing a coordinate), never lowers it, so it can never manufacture a false depth-0. Under-approximation (missing a frame the interpreter does push) is the unsafe direction and is what this list guards against by erring generous.

Implementation

bool opensLexicalFrame(SAstNode node) {
  return node is SBlock ||
      node is SForStatement ||
      node is SForElement ||
      node is SWhileStatement ||
      node is SDoStatement ||
      node is SSwitchStatement ||
      node is SSwitchExpression ||
      node is SCatchClause ||
      node is SFunctionExpression ||
      node is SMethodDeclaration ||
      node is SConstructorDeclaration;
}