flagLookup -- flag a symbol

• Usage:

  flagLookup x

• Inputs:
  • x, a symbol
• Outputs:
  • a Boolean value, whether each subsequent reference to the symbol x will result in an error message
• Consequences:

  • The first use arranges for each subsequent reference to the symbol x to result in an error message. The second use cancels the arrangement. Each subsequent use toggles the state.