Software Review - Userland Frontier

John W. Baxter

In late January, Dave Winer and the rest of the folks at Userland shipped version 1.0 of Frontier. Frontier is a tool with which you can operate the growing number of modern Macintosh applications which can be controlled by sending them suitable Apple Events. Frontier also provides a clean-looking method by which very easily changed menus can be added to an AppleEvent-savvy application (this feature is called "Menu Sharing"). Here is a brief look at Frontier.

Drive those Applications

Frontier has an easy-to-use scripting language which controls both Frontier and other AppleEvent-aware applications. The language is presented in outline form, and Frontier has a good outline editor. The structure of a script is created by the levels of the outline. For example, here is an if statement:

if people.JWB.age > 50
    msg ("John, you are getting old.")
else
    msg ("Come on, John, tell the truth")

The statements controlled by the true branch of the if statement (here, just a msg verb) are indented one outline level inferior to the if. The next statement at the same level as the if marks the end of the controlled statements. Here, that statement is an else. Again, the else controls those statements inferior to it in the outline. As with outlining programs in general, you can hide the details and see only the if and else lines if you like.

The supplied language verbs include many which are implemented in the Frontier kernel and many others which are simply scripts themselves. A full list is well beyond the scope of this column, but one handy structure for script writing is

   on explore(path)
    fileloop (aFile in path)
        if (file.isFolder(aFile))
            explore(aFile)
        else
            « do something to each aFile
            « the « introduces comments

where path identifies an HFS directory, and aFile takes on the path to each file and directory contained in that directory. You can easily recurse down through the directory levels, as shown. The on construct introduces a script (routine).

The outlining capability is useful in its own right, but is limited to single-line headers. The outline editor is fully scriptable. There is also a simple word processing editor, and word processing documents can be maintained within Frontier. That editor is suitable for writing documentation about your Frontier scripts-it is not suitable for the next great novel. The word processing editor is also fully scriptable.

Things are stored in Frontier in a database, managed as a hierarchy of tables starting at a table called root. One of the items in the root table is a table called people, which has items named with the initials of each user of a given Frontier. The first example above assumes that my table, whose full address is root.people.JWB, contains an entry named age whose value is a number. A table entry consists of a name and a value. The value may be as simple as a number or string or as complex as a word processing document, an outline or script, or any Macintosh structure stored in binary form. The set of table manipulation verbs is fully scriptable.

Whose Menus are They, Anyhow

Using AppleEvents, an application can arrange for Frontier to supply one or more menus (which can include hierarchical submenus). A simple but solid-looking protocol provides for the application to inform Frontier of selections of the items in the menus Frontier has defined. The user provides a Frontier script for each such item. That script will usually send one or more AppleEvents to the application requesting services or directing actions. Provision is made for the user to edit the menus within Frontier and for the menus to be adjusted before the next time they are pulled down by the user if they have been edited. If Frontier shuts down, the application is notified and deletes the shared menus; if Frontier launches while a menu-sharing application is running, the menus get added.

Additionally, most of Frontier's own menus are fully editable by the user. Again, each item has a script associated with it. The outline editor (slightly modified) is used to edit menus and assign the scripts.

Userland supplies source code in C for the routines that need to be added to an application to support menu sharing. I've looked at MacApp 3.0, and at this writing I have a working subclass of TApplication which supports Frontier menu sharing. Unfortunately, that subclass is not yet ready for publication.

Agent 86

One of the tables in Frontier contains "agents". These agents are scripts which receive time periodically from Frontier. Frontier ships with an agent which updates a clock in Frontier's main window. An agent can trigger arbitrarily complex scripts. Frontier is pretty good about giving processing time to agents-for example, the agents are given time while Frontier is in the background awaiting a reply to an AppleEvent it sent out as requested by a script.

Almost Faceless Mini-Applications ("Appletts")

Frontier makes sense as a controller for small, nearly faceless applications which provide simple services. This is one of the directions software is moving at the moment, the do-one-thing-and-do-it-well idea. Userland practices what they preach in this area: Frontier's on-line documentation is provided by a separate DocServer application. A control-double-click on any Frontier verb ensures that DocServer is running, sends it AppleEvents directing that the appropriate documentation be displayed, and brings DocServer to the front. There is no technical reason why DocServer wouldn't be available to your application, too. I don't know the legal details at this time.

Paper Documentation

Yes, there is some. A user manual and a scripting language ("UserTalk") reference guide were written by Dan Shafer. They explain Frontier pretty clearly, though some of the more obscure verbs are only referenced, with the DocServer material (also prepared by Dan) being the only documentation.

Apple Object Model

Frontier scripts have the power to create and send AppleEvents which make use of the Object Model. This capability should be highly useful in testing MacApp-based applications which support the Object Model and the Object Support Library. A developer may also wish to supply a suitable "suite" of Frontier scripts to the users of an application.

What's In It for Me?

If you are writing an AppleEvent-driven application, Frontier represents a potentially valuable testing and debugging tool. If your application might benefit from the shared menu idea, that is easy to add. With or without Frontier, you were going to support AppleEvents for commanding your application, weren't you? There is no extra work there (and Userland will help you prepare the file which sets up the necessary verbs in Frontier to drive your application the way you want it driven).

Besides all that, Frontier is an amusing "toy", too. I have a script which runs my FarSide calendar the first time each day that Frontier starts up (I have Frontier starting from my Startup Items folder).

Availability

Frontier is available direct from Userland. Recently, Frontier has also found its way into the mail order and retail distribution system. Userland can be found in the Third Party area on AppleLink and in their own forum on CompuServe. Their address is UserLand Software, Inc., 490 California Ave, Palo Alto, CA 94306. Telephone (415) 325-5700; fax (415) 325-9829.