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Apple called HyperCard "programming for the rest of us." Steve Wozniak called it "the best program ever written".

Released in 1987 and included in the box with every Macintosh sold during the late 1980's and '90s. HyperCard was a software Erector Set: part programming language, part paint program, part database. With HyperCard, you could draw a user interface with MacPaint-like tools, then apply scripts and behaviors to it with an expressive syntax that mimicked natural English.

Need more? Watch an interview of HyperCard's creators Bill Atkinson and Dan Winkler on The Computer Chronicles, circa 1987.

The basics

WyldCard is a clone of Apple's HyperCard, written in Java, utilizing the Swing framework for UI components and the Antlr parser generator for HyperTalk language recognition.

WyldCard lets users create and interact with a document called a stack. Like a deck of PowerPoint slides, a stack represents a navigable list of cards containing graphics and interactive user interface elements like buttons and text fields. Each card is comprised of two layers of content: a background, which can be shared between cards, and a foreground that overlays the background and which is unique to each card.

HyperTalk scripting

HyperCard's native programming language is called HyperTalk, and programs written in this language are known as scripts. Scripts describe the action that should be taken when a user interacts with a user interface element in the stack, called a part. A script might describe what should happen when a user clicks a button, chooses an item from a menu, or simply moves the mouse across the surface of the card.

As a user interacts with a stack's parts, HyperCard sends messages to them describing the nature of the interaction. Stack authors associate actions to parts by attaching a HyperTalk script that contains a message handler for each desired interaction. For example, HyperCard sends the mouseDoubleClick message to a part when the user double-clicks it with the mouse. If the script of the double-clicked part contains a handler for this message then that handler will be executed each time the part is double-clicked. Scripts can also send and respond to messages of their own invention, too.

When a message is sent to a part that has no handler to address it, the unhandled message is forwarded to other parts in the message passing order. For example, a message that's ignored by a button will be passed to the card on which the button appears. If the card also ignores the message, it gets forwarded to the background, then the stack, and finally back to WyldCard (which may provide some default behavior).

A simple script to prompt the user to enter their name then greet them might look like:

-- This is my first script. It runs when the user clicks this part.

on mouseUp
  ask "Hi! What's your name?"
  put it into theName
  if theName is not empty then answer "Pleasure to meet you, " & theName & "."
end mouseUp

HyperTalk is a dynamically typed language. Internally, WyldCard stores each value as a string of characters and interprets it as a number, boolean, list, coordinate or rectangle depending on the context of its use. The language does not allow nonsensical conversions: 5 + "12" yields 17, but 5 + "huh?" produces an error. Some have argued that HyperTalk is an object oriented programming language whose objects are its user interface elements.

Keywords and symbols in the language are case insensitive. Thus, put x into y is the same as PUt x iNTo Y. Comments are preceded by -- and terminate at the end of the line. HyperTalk has no multi-line comment syntax like, /* ... */.

Indentation and most whitespace is ignored, but newlines have special meaning in the syntax and are somewhat analogous to semicolons in C-like languages. Statements must be separated by a newline, and a single statement cannot break across multiple lines.

For example, this is legal:

answer "How are you today" with "Pretty good" or "Stinky!"

... but this is not:

answer "How are you today" with
  "Pretty good" or
  "Stinky!"

To improve readability, HyperTalk offers a line-wrap symbol (¬) that can be used to break a long statement across lines. WyldCard also allows the the pipe character (|) to be used for this purpose. Either symbol must be immediately followed by a carriage-return in order to be valid, and a quoted string literal can never be wrapped across lines. For example,

answer "This is totally acceptable!" |
  with "Love it" ¬
  or "Hate it"