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Type and existence operators

is a, is an

Results in true if the expression to its left is the same type as the type identifier on the right. The type identifiers are: number, integer, point, rect, date, and logical.

23 is a number      -- true

pi is an integer    -- false

"0,0,0" is a point  -- false

"0,0,0,0" is a rect -- true

"8/09/65" is a date -- true

false is a logical  -- true

there is a, there is an

Results in true if the expression to the right of the operator exists. The expression can take any of the following forms (with appropriate adjectives and/or names):

window    menu     menuItem   stack

file      disk     document   application

folder    picture  field      program [ID]*

button    part     scriptingLanguage

card      background

*Under system 7 only

there is no

Results in true if the expression to the right of the operator does not exist. The expression can identify the same elements as there is a.

there is no window "message watcher"

there is no menu "MayBe"

there is no menuItem "Back" of menu "Go"

there is no file "Simonides:References"

there is no stack "Home"

there is no card button 1

there is no disk "External Hard Disk"

there is no card 6

there is no bkgnd "fish bowl sizes"

there is not a

Same as the operator there is no.

Type and existence operators

is a, is an

there is a, there is an

there is no

there is not a

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