HyperTalk
|
|
HyperTalk is a high-level programming language created in 1987 by Dan Winkler and used in conjunction with Apple Computer's HyperCard hypermedia program by Bill Atkinson. The main target audience of HyperTalk was beginning programmers, hence HyperTalk programmers were usually called authors, and the process of writing programs was called "scripting". HyperTalk scripts are fairly similar to written English, and use a logic structure similar to the Pascal programming language.
The case-insensitive language was at first interpreted, but since HyperCard 2.x 'virtually compiled'. It supports the basic control structures of procedural languages: repeat for/while/until, if/then/else, as well as function and message "handler" calls (a handler is a subroutine, a message handler is a procedure). Data types are transparent to the user, conversion happens transparently in the background between strings and numbers. There are no classes or data structures in the traditional sense; their place was taken by special strings, or rather "lists" of "items" delimited by a certain character (in later versions the "itemDelimiter" property allowed choosing an arbitrary character).
| Contents |
Object-Oriented HyperTalk
However, HyperTalk was by no means a strictly procedural language. Scripts were associated with objects in HyperCard files (so-called "stacks"), and HyperTalk allowed manipulating these objects in various ways, changing their properties using the "set" command, for example. Objects were addressed using a syntax close to natural language, where objects were specified relative to the current card, or the of operator was used to specify the absolute position of an object: send "mouseUp" to card button "OK" of card "Veracity". Since buttons could also exist on the background layer, but their content would differ between cards, there were card buttons, background buttons etc. Objects could be addressed by their name, z-ordering number, or by a unique ID number that usually did not change throughout an object's lifetime. To iterate over objects (joinedly referred to as parts in HyperCard 2.2 and later), one simply used their number after querying e.g. the number of card parts.
HyperTalk also provided full-blown script control over the built-in drawing tools, simply by scripting the needed changes in paint tools and simulating mouse movements using the drag from start to endand the click at pos commands.
HyperTalk also used messages (i.e. events) sent to objects to handle user interaction. E.g. the mouseDown message was sent to a button when the user clicked it, and mouseUp was sent when the user released the mouse inside it to trigger its action. Similarly, it had the periodic idle message, mouseEnter, mouseLeave, ... and various other messages related to navigation between different cards in a HyperCard stack, as well as user input (keyDown, functionKey, ...), and system events. As far as the scripters were concerned, there were no main event loops like in other procedural programming languages.
Extending HyperTalk
Although the HyperTalk language languished just like HyperCard itself, it received a second lease on life through its plugin protocol, so-called External Commands (XCMDs) and External Functions (XFCNs), which were native code containers attached to stacks (as Macintosh-specific resources) with a single entry point and return value. XCMDs and XFCNs could be called just like regular message and function handlers from HyperTalk scripts, and were also able to send messages back to the HyperCard application. Some enterprising XCMD authors added advanced features like full color support (ColorizeHC, HyperTint, AddColor), multiple special-purpose windows (Prompt, Tabloid, Textoid, Listoid, ShowDialog, MegaWindows), drag and drop support and various hardware interfaces to the language.
Descendants of HyperTalk
Various languages have taken their cues from HyperTalk. There are straight clones like
- SuperTalk - The language of SuperCard (http://www.supercard.us) by Bill Appleton, the first HyperCard clone. Appleton also wrote the popular WorldBuilder adventure construction kit.
- PlusTalk (?) - of Spinnaker Plus (originally by the German Format Verlag), which was used as the basis for OMO.
- MediaTalk - The language of Oracle Media Objects, the first cross-platform HyperCard clone, and the only one that was truly modular.
- CompileIt!-Talk - A HyperCard stack and XCMD by Tom Pittman that allowed compiling native 68000 machine code (e.g. for XCMDs and XFCNs) from HyperTalk code, and calling the native Macintosh toolbox routines. CompileIt was bootstrapped, that is, later versions were compiled using earlier versions of itself.
- Double-XX-Talk (?) - Double-XX was a lightweight HyperCard clone that shipped as an addition to CompileIt! and allowed running XCMDs and XFCNs without HyperCard, and even included a small HyperTalk interpreter.
- Transcript (fka MetaTalk) - The language of the Unix-originated HyperCard clone Revolution (http://www.runrev.com) (formerly MetaCard (http://www.metacard.com)).
- SenseTalk - The language of the NeXT-originated HyperSense (http://www.thoughtful.com) and the VNC-based testing tool Eggplant (http://www.redstonesoftware.com/usingeggplant.html).
As well as second-level clones like
- Lingo - the programming language of Macromedia Director
- AppleScript - the main scripting language of Apple's Mac OS.
- SerfTalk - a HyperTalk-on-steroids that supported many modern features, but disappeared during its beta phase.
Many method names first popularized by HyperTalk made it into later languages, such as the onmouseUp message in JavaScript. Although Asymmetrix Toolbook is often also considered a HyperCard clone, its scripting language apparently bears little resemblance to HyperTalk.
These clones and dialects (commonly referred to under the moniker of "xTalk"-languages) added various features to the language that are expected from a modern programming language, like exception handling, user-defined object properties, timers, multi-threading and even user-defined objects.
Some sample scripts
on mouseUp
put "100,100" into pos
repeat with x = 1 to the number of card buttons
set the location of card button x to pos
add 15 to item 1 of pos
end repeat
end mouseUp
on mouseDown
put "Disk:Folder:MyFile" into filePath -- no need to declare variables
if there is a file filePath then
open file filePath
read from file filePath until return
put it into cd fld "some field"
close file filePath
set the textStyle of character 1 to 10 of card field "some field" to bold
end if
end mouseDown
function replaceStr pattern,newStr,inStr
repeat while pattern is in inStr
put offset(pattern,inStr) into pos
put newStr into character pos to (pos +the length of pattern)-1 of inStr
end repeat
return inStr
end replaceStr