| Chapter 16: Understanding |

| 16.2. New commands for old grammar

In the photography example, we are providing entirely new grammar for an action not ordinarily built in to Inform. But we often want simply to provide alternative grammar for existing actions, or even to put new interpretations on commands that Inform already recognises. For instance:

> Understand "deposit [something] in [an open container]" as inserting it into.

The inserting action is built in to Inform, but the command "deposit" is not, so this is created as new. It is occasionally useful to put a twist on this:

> Understand "fill [an open container] with [something]" as inserting it into (with nouns reversed).

The clause "(with nouns reversed)" tells Inform to exchange the two nouns parsed, which is necessary because the inserting action expects the noun to be the item and the second noun to be the container, not vice versa.

The following example:

> Understand "access [something]" as opening.

might look as if it makes "access" behave just like "open" when the player types it, but that's not so: "open" can also be used in constructions like "open the door with the brass key", in which case it is understood as the unlocking action. We could add another line to make "access" behave this way too, but if what we really want is to make "access" behave just like "open", it's easier simply to say so:

> Understand the command "access" as "open".

This is very useful when adding a new command which needs synonyms:

> Understand the commands "snap" and "picture" as "photograph".

We can check the current stock of commands by looking at the table in the Actions index: for instance, before making "snap" synonymous with "photograph", it might be wise to check that it is not already defined as a command for breaking something.

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| Example Anchorite By default, Inform understands GET OFF, GET UP, or GET OUT when the player is sitting or standing on an enterable object. We might also want to add GET DOWN and DOWN as exit commands, though:

With GET DOWN, we can replace the whole command, which will not interfere with the normal function of the TAKE verb, or allow the player to attempt to GET any other directions: "Anchorite" The Solitary Place is a room. "A glittering, shimmering desert without either locusts or honey." The pillar is an enterable supporter in the Solitary Place. "The broken pillar is short enough to climb and sit on." The description of the pillar is "Once it was a monument: a long frieze of battles and lion-hunts spirals up the side, in honor of an earthly king." The player is on the pillar. Understand "get down" as exiting. This doesn't cover the case where the player just types "DOWN", and we don't want to preempt the normal operation of the GO action here. So instead of writing a new understand instruction, we might catch this one at the action-processing level: Instead of going down when the player is on a supporter: try exiting. Test me with "down / enter pillar / get down / down / get down".

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| Example Alpaca Farm A generic USE action which behaves sensibly with a range of different objects, expanding on the EMPLOY example above.

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| Example Cloak of Darkness Implementation of "Cloak of Darkness", a simple example game that for years has been used to demonstrate the features of IF languages.

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