LTAI Error Handling (4)
Context stack (with associated error messages)
Error look-up table
onlyOne There is only one value noMore There is no more value Empty The workspace is empty NIL The value is nil TooBig The result is too big TooSmall The result is too small NoValue There is no value in the workspace Highest level error response: "I cannot <operation>, because <error>"
User asks "Why?" to progress down tree
At each node, the command is explained and an error given
User asks "Then?" to move onto the next right node to gain more information
System responds: "That is all." when tree search exhausted
