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<HTML><HEAD><TITLE>Section A6: Library properties</TITLE></HEAD>
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<BODY BGCOLOR="#FFFFFF">
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<TR><TD Valign="top"><A HREF="contents.html">Contents</A><BR><A HREF="sectionA5.html">Back</A><BR><A HREF="sectionA7.html">Forward</A><TD bgcolor="#F5DEB3"><BLOCKQUOTE><H3>A6. Library properties</H3></BLOCKQUOTE><TR><TD><TD>
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The following table lists every library-defined property. The banner
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headings give the name, what type of value makes sense and the default value
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(if other than 0). The symbol
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means "this property is additive''
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so that inherited values from class definitions pile up into a list, rather
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than wipe each other out. Recall that 'false' is the value 0 and 'true'
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>n_to, s_to, e_to, w_to, ...</B></TT> -- Room, object or routine<TR><TD><TD>
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<BR><I>For rooms: </I>These twelve properties (there are also <TT>ne_to</TT>, <TT>nw_to</TT>, <TT>se_to</TT>,
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<TT>sw_to</TT>, <TT>in_to</TT>, <TT>out_to</TT>, <TT>u_to</TT> and <TT>d_to</TT>) are the map connections for
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the room. A value of 0 means "can't go this way''. Otherwise, the
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value should either be a room or a <TT>door</TT> object: thus, <TT>e_to</TT> might be set
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to <TT>crystal_bridge</TT> if the direction "east'' means "over the crystal
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<BR><I>Routine should return:</I> The room or object the map connects to; or 0 for "can't go this way'';
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or 1 for "can't go this way; stop and print nothing further''.
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<BR><I>Warning: </I> Do not confuse the direction properties <TT>n_to</TT> and so on with
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the twelve direction objects, <TT>n_obj</TT> et
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>add_to_scope</B></TT> -- List of objects or routine<TR><TD><TD>
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<BR><I>For objects: </I>When this object is in scope, so are all those listed, or all those
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nominated by the routine. A routine given here should call
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<TT>PlaceInScope(obj)</TT> to put <TT>obj</TT> in scope.
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD Valign="top"><B>(+)</B><TD bgcolor="#AE9BFF"><TT><B>after</B></TT> -- Routine (<TT>NULL</TT>)<TR><TD><TD>
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Receives actions after they have happened, but before the player has
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<BR><I>For rooms: </I>All actions taking place in this room.
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<BR><I>For objects: </I>All actions for which this object is <TT>noun</TT> (the first object
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specified in the command); and all fake actions for it.
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<BR><I>Routine should return:</I> False to continue (and tell the player what has happened), true to
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stop here (printing nothing).
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The <TT>Search</TT> action is a slightly special case. Here, <TT>after</TT> is
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called when it is clear that it would be sensible to look inside the object
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(e.g., it's an open container in a light room) but before the contents
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>article</B></TT> -- String or routine (<TT>"a"</TT>)<TR><TD><TD>
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<BR><I>For objects: </I>Indefinite article for object or routine to print one.
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>articles</B></TT> -- Array of strings<TR><TD><TD>
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For objects: If given, these are the articles used with
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the object's name. (Provided for non-English languages
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where irregular nouns may have unusual vowel-contraction
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rules with articles: e.g. with French non-mute 'H'.)
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<P><TR><TD Valign="top"><B>(+)</B><TD bgcolor="#AE9BFF"><TT><B>before</B></TT> -- Routine (<TT>NULL</TT>)<TR><TD><TD>
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Receives advance warning of actions (or fake actions) about to happen.
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<BR><I>For rooms: </I>All actions taking place in this room.
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<BR><I>For objects: </I>All actions for which this object is <TT>noun</TT> (the first object
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specified in the command); and all fake actions, such as <TT>Receive</TT>
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and <TT>LetGo</TT> if this object is the container or supporter concerned.
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<BR><I>Routine should return:</I> False to continue with the action, true to stop here (printing
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First special case: A vehicle object receives the <TT>Go</TT>
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action if the player is trying to drive around in it. In this case:
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<BR><I>Routine should return:</I> 0 to disallow as usual; 1 to allow as usual, moving vehicle and
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player; 2 to disallow but do (and print) nothing; 3 to allow but do
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(and print) nothing. If you want to move the vehicle in your own code,
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return 3, not 2: otherwise the old location may be restored by subsequent
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Second special case: in a <TT>PushDir</TT> action, the <TT>before</TT>
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routine must call <TT>AllowPushDir()</TT> and then return true in order to
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allow the attempt (to push an object from one room to another) to
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>cant_go</B></TT> -- String or routine (<TT>"You can't go that way."</TT>)<TR><TD><TD>
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<BR><I>For rooms: </I>Message, or routine to print one, when a player tries to go in an
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impossible direction from this room.
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>capacity</B></TT> -- Number or routine (<TT>100</TT>)<TR><TD><TD>
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<BR><I>For objects: </I>Number of objects a <TT>container</TT> or <TT>supporter</TT>
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<BR><I>For player objects: </I>Number of things the player can carry (when the player is this
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object); the default player object (<TT>selfobj</TT>) has <TT>capacity</TT> initially
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set to the constant <TT>MAX_CARRIED</TT>.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>daemon</B></TT> -- Routine (<TT>NULL</TT>)<TR><TD><TD>
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This routine is run each turn, once it has been activated by a
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call to <TT>StartDaemon</TT>, and until stopped by a call to <TT>StopDaemon</TT>.
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<P><TR><TD Valign="top"><B>(+)</B><TD bgcolor="#AE9BFF"><TT><B>describe</B></TT> -- Routine (<TT>NULL</TT>)<TR><TD><TD>
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<BR><I>For objects: </I>Called when the object is to be described in a room description,
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before any paragraph break (i.e., skipped line) has been printed. A
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sometimes useful trick is to print nothing in this routine and return
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true, which makes an object 'invisible'.
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<BR><I>For rooms: </I>Called before a room's long ("look'') description is printed.
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<BR><I>Routine should return:</I> False to describe in the usual way, true to stop printing here.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>description</B></TT> -- String or routine<TR><TD><TD>
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<BR><I>For objects: </I>The <TT>Examine</TT> message, or a routine to print one out.
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<BR><I>For rooms: </I>The long ("look'') description, or a routine to print one out.
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>door_dir</B></TT> -- Direction property or routine<TR><TD><TD>
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<BR><I>For compass objects: </I>When the player tries to go in this direction, e.g., by typing the
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name of this object, then the map connection tried is the value of
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this direction property for the current room. For example, the
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<TT>n_obj</TT> "north'' object normally has <TT>door_dir</TT> set to <TT>n_to</TT>.
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<BR><I>For objects: </I>The direction that this <TT>door</TT> object goes via (for instance,
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a bridge might run east, in which case this would be set to <TT>e_to</TT>).
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<BR><I>Routine should return:</I> The direction property to try.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>door_to</B></TT> -- Room or routine<TR><TD><TD>
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<BR><I>For objects: </I>The place this door object leads to. A value of 0 means
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<BR><I>Routine should return:</I> The room. Again, 0 (or false) means "leads nowhere''.
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Further, 1 (or true) means "stop the movement action immediately
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and print nothing further''.
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<P><TR><TD Valign="top"><B>(+)</B><TD bgcolor="#AE9BFF"><TT><B>each_turn</B></TT> -- String or routine (<TT>NULL</TT>)<TR><TD><TD>
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String to print, or routine to run, at the end of each turn in which
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the object is in scope (after all timers and daemons for that turn have
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>found_in</B></TT> -- List of rooms or routine<TR><TD><TD>
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This object will be found in all of the listed rooms, or if
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the routine says so, unless it has the attribute <TT>absent</TT>. If
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an object in the list is not a room, it means "present in the
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same room as this object''.
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<BR><I>Routine should return:</I> True to be present, otherwise false. The routine can look
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at the current <TT>location</TT> in order to decide.
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<BR><I>Warning: </I>This property is only looked at when the player changes rooms.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>grammar</B></TT> -- Routine<TR><TD><TD>
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<BR><I>For animate or talkable objects: </I> This is called when the
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parser has worked out that the object in question is being spoken
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to, and has decided the <TT>verb_word</TT> and <TT>verb_wordnum</TT> (the position
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of the verb word in the word stream) but hasn't yet tried any grammar.
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The routine can, if it wishes, parse past some words (provided it
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moves <TT>verb_wordnum</TT> on by the number of words it wants to eat up).
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<BR><I>Routine should return:</I> False to carry on as usual; true to indicate that the routine
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has parsed the entire command itself, and set up <TT>action</TT>, <TT>noun</TT>
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and <TT>second</TT> to the appropriate order; or a dictionary value for
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a verb, such as <TT>'take'</TT>, to indicate "parse the command from this
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verb's grammar instead''; or minus such a value, e.g. <TT>-'take'</TT>,
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to indicate "parse from this verb and then parse the usual
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>initial</B></TT> -- String or routine<TR><TD><TD>
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<BR><I>For objects: </I>The description of an object not yet picked up, used when a
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room is described; or a routine to print one out.
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<BR><I>For rooms: </I>Printed or run when the room is arrived in, either by ordinary
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movement or by <TT>PlayerTo</TT>.
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<BR><I>Warning: </I>If the object is a <TT>door</TT>, or a <TT>container</TT>, or is <TT>switchable</TT>,
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then use one of the <TT>when_</TT> properties rather than <TT>initial</TT>.
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>inside_description</B></TT> -- String or routine<TR><TD><TD>
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<BR><I>For objects: </I>Printed as part or all of a room description when the player is
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inside the given object, which must be <TT>enterable</TT>.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>invent</B></TT> -- Routine<TR><TD><TD>
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This routine is for changing an object's inventory listing. If provided,
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it's called twice, first with the variable <TT>inventory_stage</TT> set to 1,
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second with it set to 2. At stage 1, you have an entirely free hand to
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print a different inventory listing.
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<BR><I>Routine should return:</I> Stage 1: False to continue; true to stop here, printing nothing further
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about the object or its contents.
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At stage 2, the object's indefinite article and short name have
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already been printed, but messages like " (providing light)'' haven't.
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This is an opportunity to add something like " (almost empty)".
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<BR><I>Routine should return:</I> Stage 2: False to continue; true to stop here, printing nothing further
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about the object or its contents.
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<P><TR><TD Valign="top"><B>(+)</B><TD bgcolor="#AE9BFF"><TT><B>life</B></TT> -- Routine (<TT>NULL</TT>)<TR><TD><TD>
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This routine holds rules about <TT>animate</TT> objects, behaving much like
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<TT>before</TT> and <TT>after</TT> but only handling the person-to-person events:
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Attack Kiss WakeOther ThrowAt Give Show Ask Tell Answer Order
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See <A HREF="section16.html">Section 16</A>, and see also the properties <TT>orders</TT> and <TT>grammar</TT>.
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<BR><I>Routine should return:</I> True to stop and print nothing, false to resume as usual (for example,
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printing "Miss Gatsby has better things to do.'').
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>list_together</B></TT> -- Number, string or routine<TR><TD><TD>
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Objects with the same <TT>list_together</TT> value are grouped together in
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object lists (such as inventories, or the miscellany at the end of a
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room description). If a string such as <TT>"fish"</TT> is given, then such
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a group will be headed with text such as <TT>"five fish"</TT>.
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A routine, if given, is called at two stages in the process
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(once with the variable <TT>inventory_stage</TT> set to 1, once with it set to 2).
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These stages occur before and after the group is printed; thus, a
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preamble or postscript can be printed. Also, such a routine may
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change the variable <TT>c_style</TT> (which holds the current list style).
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On entry, the variable <TT>parser_one</TT> holds the first object in the
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group, and <TT>parser_two</TT> the current depth of recursion in the list.
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Applying <TT>x=NextEntry(x,parser_two);</TT> moves <TT>x</TT> on from <TT>parser_one</TT>
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to the next item in the group. Another helpful variable is
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<TT>listing_together</TT>, set up to the first object of a group being listed
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(or to 0 whenever no group is being listed).
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<BR><I>Routine should return:</I> Stage 1: False to continue, true not to print the group's list
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<BR><I>Routine should return:</I> Stage 2: No return value.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>orders</B></TT> -- Routine<TR><TD><TD>
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<BR><I>For animate or talkable objects: </I> This carries out the player's
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orders (or doesn't, as it sees fit): it looks at <TT>actor</TT>, <TT>action</TT>,
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<TT>noun</TT> and <TT>second</TT> to do so. Unless this object is the current
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player, <TT>actor</TT> is irrelevant (it is always the player) and the
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object is the person being ordered about.
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If the player typed an incomprehensible command, like
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"robot, og sthou'', then the action is <TT>NotUnderstood</TT> and the
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variable <TT>etype</TT> holds the parser's error number.
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If this object is the current player then <TT>actor</TT> is
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the person being ordered about. <TT>actor</TT> can either be this
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object -- in which case an action is being processed, because
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the player has typed an ordinary command -- or can be some other
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object, in which case the player has typed an order. See
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<A HREF="section16.html">Section 16</A> for how to write <TT>orders</TT> routines in these cases.
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<BR><I>Routine should return:</I> True to stop and print nothing further; false to continue.
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(Unless the object is the current player, the <TT>life</TT> routine's
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<TT>Order</TT> section gets an opportunity to meddle next; after that,
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<P><TR><TD Valign="top"><B>(+)</B><TD bgcolor="#AE9BFF"><TT><B>name</B></TT> -- List of dictionary words<TR><TD><TD>
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<BR><I>For objects: </I>A list of dictionary words referring to this object.
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<BR><I>Warning: </I>The <TT>parse_name</TT> property of an object may take precedence over this,
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<BR><I>For rooms: </I>A list of words which the room understands but which refer to things
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which "do not need to be referred to in this game''; these are only looked
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at if all other attempts to understand the player's command have failed.
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<BR><I>Warning: </I>Uniquely in Inform syntax, these dictionary words are given in double
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quotes <TT>"thus"</TT>, whereas in all other circumstances they would be <TT>'thus'</TT>.
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This means they can safely be only one letter long without ambiguity.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>number</B></TT> -- Any value<TR><TD><TD>
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A general purpose property left free: conventionally holding a number like
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"number of turns' battery power left''.
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<BR><I>For compass objects: </I>Note that the standard compass objects defined by the library all
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provide a <TT>number</TT> property, in case this might be useful to the designer.
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<BR><I>For player objects: </I>Exception: an object to be used as a player-object must provide one of
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these, and musn't use it for anything.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>parse_name</B></TT> -- Routine<TR><TD><TD>
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<BR><I>For objects: </I>To parse an object's name (this overrides the <TT>name</TT> but is also used in
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determining if two objects are describably identical). This routine should
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try to match as many words as possible in sequence, reading them one at a
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time by calling <TT>NextWord()</TT>. (It can leave the "word marker'' variable
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<TT>wn</TT> anywhere it likes).
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<BR><I>Routine should return:</I> 0 if the text didn't make any sense at all, -1 to make the parser resume
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its usual course (looking at the <TT>name</TT>), or the number of words in a row
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which successfully matched.
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In addition to this, if the text matched seems to be in the plural
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(for instance, a blind mouse object reading <TT>blind mice</TT>), the routine can
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set the variable <TT>parser_action</TT> to the value <TT>##PluralFound</TT>. The parser
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will then match with all of the different objects understood, rather than
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ask a player which of them is meant.
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A <TT>parse_name</TT> routine may also (voluntarily) assist the parser
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by telling it whether or not two objects which share the same <TT>parse_name</TT>
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routine are identical. (They may share the same routine if they both inherit
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it from a class.) If, when it is called, the variable <TT>parser_action</TT> is
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set to <TT>##TheSame</TT> then this is the reason. It can then decide whether or
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not the objects <TT>parser_one</TT> and <TT>parser_two</TT> are indistinguishable.
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<BR><I>Routine should return:</I> -1 if the objects are indistinguishable, -2 if not.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>plural</B></TT> -- String or routine<TR><TD><TD>
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<BR><I>For objects: </I>The plural name of an object (when in the presence of others like it),
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or routine to print one; for instance, a wax candle might have <TT>plural</TT> set
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to <TT>"wax candles"</TT>.
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>react_after</B></TT> -- Routine<TR><TD><TD>
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<BR><I>For objects: </I>Acts like an <TT>after</TT> rule, but detects any actions in the vicinity
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(any actions which take place when this object is in scope).
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<BR><I>Routine should return:</I> True to print nothing further; false to carry on.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>react_before</B></TT> -- Routine<TR><TD><TD>
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<BR><I>For objects: </I>Acts like a <TT>before</TT> rule, but detects any actions in the vicinity
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(any actions which take place when this object is in scope).
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<BR><I>Routine should return:</I> True to stop the action, printing nothing; false to carry on.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>short_name</B></TT> -- Routine<TR><TD><TD>
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<BR><I>For objects: </I>The short name of an object (like "brass lamp"), or a routine to print
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<BR><I>Routine should return:</I> True to stop here, false to carry on by printing the object's 'real'
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short name (the string given at the head of the object's definition). It's
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sometimes useful to print text like <TT>"half-empty "</TT> and then return false.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>short_name_indef</B></TT> -- Routine<TR><TD><TD>
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<BR><I>For objects: </I>If set, this form of the short name is used
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when the name is prefaced by an indefinite article. (This
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is not useful in English-language games, but in other
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languages adjectival parts of names agree with the
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definiteness of the article.)
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>time_left</B></TT> -- Number<TR><TD><TD>
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Number of turns left until the timer for this object (if set, which must be
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done using <TT>StartTimer</TT>) goes off. Its initial value is of no significance,
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as <TT>StartTimer</TT> will write over this, but a timer object must provide the
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property. If the timer is currently set, the value 0 means "will go off
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at the end of the current turn'', the value 1 means "...at the end of
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next turn'' and so on.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>time_out</B></TT> -- Routine (<TT>NULL</TT>)<TR><TD><TD>
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Routine to run when the timer for this object goes off (having been set by
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<TT>StartTimer</TT> and not in the mean time stopped by <TT>StopTimer</TT>).
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<BR><I>Warning: </I>A timer object must also provide a <TT>time_left</TT> property.
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>when_closed</B></TT> -- String or routine<TR><TD><TD>
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<BR><I>For objects: </I>Description, or routine to print one, of something closed (a <TT>door</TT> or
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<TT>container</TT>) in a room's long description.
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>when_open</B></TT> -- String or routine<TR><TD><TD>
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<BR><I>For objects: </I>Description, or routine to print one, of something open (a <TT>door</TT> or
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<TT>container</TT>) in a room's long description.
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>when_on</B></TT> -- String or routine<TR><TD><TD>
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<BR><I>For objects: </I>Description, or routine to print one, of a <TT>switchable</TT> object which is
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currently switched on, in a room's long description.
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>when_off</B></TT> -- String or routine<TR><TD><TD>
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<BR><I>For objects: </I>Description, or routine to print one, of a <TT>switchable</TT> object which is
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currently switched off, in a room's long description.
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<BR><I>No return value expected from routine.</I>
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<P><TR><TD><TD bgcolor="#AE9BFF"><TT><B>with_key</B></TT> -- Object (<TT>nothing</TT>)<TR><TD><TD>
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The key object needed to lock or unlock this <TT>lockable</TT> object. A player
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must explicitly name it as the key being used and be holding it at the time.
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The value <TT>nothing</TT>, or 0, means that no key fits (though this is not made
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clear to the player, who can try as many as he likes).
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<HR><A HREF="contents.html">Contents</A> / <A HREF="sectionA5.html">Back</A> / <A HREF="sectionA7.html">Forward</A> <BR>
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<A HREF="chapter1.html">Chapter I</A> / <A HREF="chapter2.html">Chapter II</A> / <A HREF="chapter3.html">Chapter III</A> / <A HREF="chapter4.html">Chapter IV</A> / <A HREF="chapter5.html">Chapter V</A> / <A HREF="chapter6.html">Chapter VI</A> / <A HREF="chapterA.html">Appendix</A><HR><SMALL><I>Mechanically translated to HTML from third edition as revised 16 May 1997. Copyright © Graham Nelson 1993, 1994, 1995, 1996, 1997: all rights reserved.</I></SMALL></BODY></HTML>
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