Error running script: Error compiling expression 'exit.visible': RootExpressionElement: Cannot convert type 'Object' to expression result of 'Boolean'

I do not have an exit.variable in my code. In fact I never referenced any variable called "visible". Why am I be getting this error?

There are two places in the core code the expression exit.visible appears.

First is in the function ScopeExitsForRoom, which looks like this:

  <function name="ScopeExitsForRoom" type="objectlist" parameters="room">
    <![CDATA[
    result = NewObjectList()
    foreach (exit, AllExits()) {
      if (exit.parent = room) {
        if (exit.visible) {
          if (GetBoolean(room, "darklevel")) {
            if (GetBoolean(exit, "lightsource")) {
              list add(result, exit)
            }
          }
          else {
            list add(result, exit)
          }
        }
      }
    }
    return (result)
    ]]>
  </function>

Now, in this case the variable exit is being extracted from the built-in function AllExits(), so it can only be an exit. And all exits inherit the type defaultexit, which forces them to have a visible attribute. So if the error is coming from here, it means that either you have modified defaultexit and omitted the visible attribute; or you have created an exit whose visible attribute is set to an actual object.

Both of these seem unlikely, so let's look at the other possibility.

The built-in go command starts with:

  <command name="go" pattern="[go]" unresolved="[UnresolvedLocation]">
    if (exit.visible) {
      if (exit.locked) {
        msg (exit.lockmessage)
      }
      else if (exit.runscript) {
        if (HasScript(exit, "script")) {
          do (exit, "script")
        }
      }
      else if (exit.lookonly) {
         msg ("[UnresolvedLocation]")
      }
      else {
        if (HasString(exit, "message")) {
          if (not exit.message = "") {
            if (game.clearscreenonroomenter) {
              game.currentexitmessage = exit.message
            }
            else {
              msg(exit.message)
            }
          }
        }
        game.pov.parent = exit.to
      }
    }
    else {
      msg ("[UnresolvedLocation]")
    }
  </command>

Hmm… the parser's scope functions should ensure that this only gets an exit as well. Or are you invoking the go script manually? I would wonder if you were passing an object to go.script using some of your own code; but that still shouldn't cause that error, as defaultobject also has a boolean visible attribute. Are you manually invoking go.script and passing it a command or a turnscript in place of an exit for some reason?

So… further questions:

• Have you modified defaultexit?
• Does the error appear as soon as the game starts, at some specific interval, or when the player uses the go command?
• Have you manually called go.script anywhere in your code? If so, what exit are you passing it?

With a weird case like this, it would probably be better if you could just show us a copy of the game (or a sample game that demonstrates the same error). This is the kind of issue where explaining what to look for can be tough, but it should stand out to a more experienced user.

So if the error is coming from here, it means that either you have modified defaultexit and omitted the visible attribute; or you have created an exit whose visible attribute is set to an actual object.
Both of these seem unlikely, so let's look at the other possibility.

Oops

<type name="defaultexit">
    <access_requirement type="string"></access_requirement>
    <action_description type="string"></action_description>
    <display_when_out_of_combat type="string"></display_when_out_of_combat>
    <display_during_close_combat type="string"> </display_during_close_combat>
    <can_push_to type="boolean">true</can_push_to>
    <can_fall_down type="boolean">false</can_fall_down>
  </type>

I am hoping to have exits that don't require me to keep manually updating each one individually as I develop my game. Is there a way to add what I have above to "defaultexit" without removing what is already in it?

The usual way to do stuff like that is for the code that uses those attributes to check if they exist, and if not use a default value.

I've also seen people redefine the type direction, which by default is inherited by all directional exits, but doesn't contain any attributes you would need to preserve.]

If you really want to modify defaultexit itself, to ensure that your attributes appear on all exits, you would need to include some of the default attributes.

I assume you've seen the default definition?

  <type name="defaultexit">
    <displayverbs type="simplestringlist">[GoTo]</displayverbs>
    <visible type="boolean">true</visible>
    <scenery type="boolean">false</scenery>
    <locked type="boolean">false</locked>
    <lockmessage>[LockedExit]</lockmessage>
    <lookonly type="boolean">false</lookonly>
    <runscript type="boolean">false</runscript>
    <lightstrength type="string"></lightstrength>
    <grid_length type="int">1</grid_length>
    <grid_render type="boolean">false</grid_render>
    <grid_offset_x type="int">0</grid_offset_x>
    <grid_offset_y type="int">0</grid_offset_y>
  </type>

Core scope functions use the attributes visible and scenery, so you will need to include those unless you are rewriting the scope functions too. (They also use lightsource and lightstrength, but those are checked using the GetBoolean and GetString functions, so omitting them doesn't cause an error)

So you'd end up with something like:

  <type name="defaultexit">
    <visible type="boolean">true</visible>
    <scenery type="boolean">false</scenery>
    <access_requirement type="string"></access_requirement>
    <action_description type="string"></action_description>
    <display_when_out_of_combat type="string"></display_when_out_of_combat>
    <display_during_close_combat type="string"> </display_during_close_combat>
    <can_push_to type="boolean">true</can_push_to>
    <can_fall_down type="boolean">false</can_fall_down>
  </type>

The grid_ attributes are used by the grid/map system, so should be included as well if you want to use the map at all.

The remaining attributes (locked, lookonly, runscript, and to) are referenced by the default go command; so if you've written your own go you can probably omit them.

Everything related to this issue seems to be fixed now! Thanks for all the help mrangel!