Expressions

Chunks | Operators | Factors | Literals

An expression is any fragment of HyperTalk that represents or produces a value.

Literals ("Hello!"), constants (pi), containers, (the first line of card field 1), properties (the name of me), operators (2 + 2) and functions (the short date) are all expressions.

Some examples of valid expressions include:

item 1 of the mouseLoc < 100 -- true if the mouse is towards the left of the card
4 * (2 + 3) -- yields 20
"hello" contains "el" and "goodbye" contains "bye" -- true
3 * 5 is not 15 -- false
"Hello" && "World" -- produces "Hello World"
"Hyper" > "Card" -- true, "Hyper" is alphabetically after "Card"
not "nonsense" -- syntax error, "nonsense" is not a boolean
false is not "tr" & "ue" -- true, concatenating 'tr' with 'ue' produces a logical value

Chunks

HyperTalk provides a powerful syntax for addressing just a portion of an expression, called a chunk.

That is, a script can get or set any range of words, characters, lines, or comma-separated items of a value by specifying them numerically (line 3 of), positionally (the last line of, the middle word of), randomly (any item of), or ordinally (the third line of).

For example, consider these chunked expressions:

the first character of the second word of the last line of field id 24
character 19 to 27 of the message box
the second item of "Hello,Goodbye" -- yields "Goodbye"
the middle word of "one two three" -- yields "two"

When modifying a chunk of an expression, a preposition (before, into, or after) must be included in the put command. For example:

put word 2 of "Hello Goodbye" into the first word of field id 0
put "blah" after the third character of the middle item of myVar
put 29 before the message box

Chunks can be used as terms in an expression to produce powerful and easy-to-understand logic:

multiply the first character of card field "numbers" by 9
if item 1 of the mouseLoc > item 2 of the mouseLoc then answer "Move left, captain!"
sort the lines of bkgnd field 3 by the last word of each

HyperTalk even lets you to modify a chunk-of-a-chunk (or a chunk-of-a-chunk-of-a-chunk). For example:

put "x" into the second character of the third word of the fourth line of field id 1
put the first char of the second word of myContainer into the middle item of the last line of y

Operators

An operator is an expression that takes one or two values (called operands) and performs some operation on them that yields a new value.

As in mathematics, higher precedence operators are evaluated before lower precedence operators irrespective of their lexical order in the expression. For example, 2 + 3 * 4 yields 14, not 20, because the * operator has higher precedence than the + operator.

HyperTalk provides this suite of mathematical, logical, and string operators:

Precedence	Operator	Description
1 (highest)	( )	Grouping
2	-	Negation for numbers (unary)
	not	Negation for logical values (unary)
	there is a[n]	Determines if the expression to the right of the operator refers to an existent stack part (unary)
	there is not a[n], there is no	Negation of object existence (unary)
3	^	Exponentiation for numbers
4	*	Multiplication for numbers
	/	Division for numbers
	div	Division for numbers
	mod	Modulus division for numbers (returns the remainder)
5	+	Addition for numbers
	-	Subtraction for numbers
6	&	Text concatenation; "a" & "b" yeilds ab
	&&	Text concatenation by adding a space between operators; "a" && "b" yeilds a b
7	>	Greater than comparison for numbers and text
	<	Less than comparison for numbers and text
	<=, ≤	Less than or equal to comparison for numbers and text
	>=, ≥	Greater than or equal to comparison for numbers and text
	contains, is in	Substring comparison for text; "hell" is in "hello" yeilds true
	is a[n]	Determines if the left-hand value is a number, integer, date, point, rect (or rectangle), logical (or boolean, bool). Returns an error if the right-hand value is not an expression yielding one of these types.
	is not a[n]	The logical inverse of is a, is an
8	=, is	Equality comparison for text, arithmetic or logical values
	is not, <>, ≠	Negative equality comparison; the inverse of =, is
	is within	Determines if the left-hand point value is contained within the right-hand rectangle value
	is not within	Determines if the left-hand point value is not contained within the right-hand rectangle value
9	and	Logical AND for boolean values
10 (lowest)	or	Logical OR for boolean values

Factors

A factor is an expression that refers to a part (like a card, button or field), which WyldCard interprets in whatever way is most meaningful to the context of its usage. Factors have the effect of making HyperTalk feel more like English than a computer programming language. Factors "do what I mean, not what I say."

For example, the go command expects to "go" to a navigable destination like a card or background. But, if you say go to cd field 1, WyldCard will assume that you mean to go wherever the text of that field refers, because a field is not a valid argument to go. Of course, if no such field exists, or if the text contained in that field doesn't actually refer to a navigable destination (such as card 3 of stack "Fun Games") then WyldCard will produce an error.

This behavior is true of other commands that expect a reference to part as an argument.

How factors work in WyldCard

When a HyperTalk command expects an argument conforming to a specific object type (like a button), it uses this algorithm to determine how to interpret the factor:

1. If the argument expression is a grouped expression (that is, it has parentheses around it) then the expression inside the parens is evaluated and the resulting value is re-interpreted as a HyperTalk expression. If the re-interpreted expression refers to an object of the expected type, then that object becomes the argument to the command. For example, consider a card in which card field 1 contains the text card button 1. On this card, the command hide card field 1 has the effect of hiding the first card field, but, the command hide (card field 1) hides the button card button 1, not the field.

2. If the expression is an object literal referring directly to the expected object type, then the literal value is accepted as the argument to the command. In the previous example, removing the parentheses from the command causes the field itself to be hidden because card field 1 is an acceptable object literal for the hide command.

3. Finally, if the previous attempts don't produce a usable argument, then the expression is evaluated, and the result is treated as the argument. For example, when executing the command hide x, we find that x is neither a grouped expression, nor is it an object literal. HyperTalk then attempts to evaluate x as an expression. If a variable called x exists, then the value of that variable is treated as the argument to hide.

Constants and literals

The table below lists special values that are treated as constants in the language. These are special keywords in the syntax whose unquoted use always evaluates to the specified value. For example, put 3 + ten displays 13 inside the message window.

Constant	Value
empty	The empty string, equivalent to ""
pi	The first 20 digits of pi, 3.14159265358979323846
quote	A double-quote character, "
return	The newline character (\n in Java)
space	A single space, equivalent to " "
tab	A tab character
formFeed	The form feed character (ASCII 0x0c, \f in Java)
lineFeed	The line feed character (ASCII 0x0a, \r in Java)
comma	The comma character, ,
colon	The colon character, :
zero..ten	The integers 0 to 10

Any single-word unquoted literal that is not a language keyword or an in-scope variable will be interpreted as though it were a quoted string literal. For example, put neat into x is equivalent to put "neat" into x. Multi-word unquoted literals are never allowed in WyldCard (e.g., put hello world results in a syntax error).