sclass LASScope {
  // do we use FixedVarContext instead of FlexibleVarContext
  settable bool useFixedVars;
  
  // variables declared in this scope, with type/value description
  gettable new Map<S, LASValueDescriptor> declaredVars;
  
  // optional parent scope
  // (we can see the parent's variables in this scope too, unless they
  // are redeclared)
  settable LASScope parentScope;
  
  // true = we may outlive the parent scope
  // (e.g. when we're a lambda)
  settable bool parentIsDetached;
  
  // sorted names when scope is finalized (resolved)
  S[] names;
  
  *() {}
  *(LASScope *parentScope) {}
  
  bool resolved() { ret names != null; }
  
  void addDeclaredVar(S name, LASValueDescriptor type) {
    if (resolved())
      fail("Can't add variables to resolved scope");
    declaredVars.put(name, type);
  }
  
  int resolveVar(S name) {
    resolve();
    int idx = indexOfInSortedArray(names, name);
    if (idx < 0)
      fail("Variable not found in scope: " + name);
    ret idx;
  }
  
  void resolve {
    if (names != null) ret;
    names = empty(declaredVars) ? null
      : toStringArray(sortedKeys(declaredVars));
  }
}

Began life as a copy of #1035285