Expression getExpression(String varName)

Returns the bound expression for the given variable. Performs recursive lookup through parentScope.

Throws a StateError, if variable is still unbound at the root scope.

Source 

Expression getExpression(String varName) {
  if (variables.containsKey(varName)) {
    return variables[varName];
  } else if (parentScope != null) {
    return parentScope.getExpression(varName);
  } else {
    throw new StateError('Variable not bound: $varName');
  }
}