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§6.17. Clarification and Correction

Some commands and some objects raise special challenges when it comes to working out the player's intention.

Sometimes this can be done with good rules about the assumptions Inform should make. Alpaca Farm demonstrates a USE command, always a challenge because USE can mean very different actions with different items.

There are also times when we need to ask the player for more information. Apples demonstrates how sensibly to use properties to disambiguate between similar objects, while Walls and Noses rephrases the disambiguation question when special objects are involved: examining one of the walls of the room will make the story ask "In which direction?" and EXAMINE NOSE will lead to "Whose nose do you mean, Frederica's, Betty's, Wilma's or your own?"

At other times, the player types something that is wrong in a predictable way: for instance, we might want to remove all the "with..." phrases from commands like


and merely parse the remainder of the command. (That last command may be unlikely, but novice players do quite often type commands that refer unnecessarily to body parts.) Cave-troll demonstrates how.

WXPQ demonstrates how to modify the error message the parser gives in response to a command it doesn't understand; this particular example focuses on the "That noun doesn't make sense in this context" message that arises from using the "[any thing]" or "[any room]" tokens, but the techniques could be adapted to handling other parser errors as well.

For catching typing errors, Cedric Knight's extension Mistype may also be of use: it provides an automatic typo-correction function that the player can turn on or off.

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*ExampleAlpaca Farm
A generic USE action which behaves sensibly with a range of different objects.

Prompting the player on how to disambiguate otherwise similar objects.

Creating a more sensible parser error than "that noun did not make sense in this context".

***ExampleWalls and Noses
Responding to "EXAMINE WALL" with "In which direction?", and to "EXAMINE NOSE" with "Whose nose do you mean, Frederica's, Betty's, Wilma's or your own?"

Determining that the command the player typed is invalid, editing it, and re-examining it to see whether it now reads correctly.