Sets I

Sets are constructed with square brackets preceded by a colon. Elements are separated by one or more whitespaces. Sets can contain any valid Wall element. Since we have already seen symbols, we'll use some for demonstration purposes.

w> apple banana pear =
w> :[ apple banana pear ]
:[ apple banana pear ]

Sets are just functions whose domain contains all valid Wall values and whose range contains true and false. All elements present in the set produce true, and all elements not present in the set produce false. Thus, the following code is valid Wall syntax.

w> apple banana pear =
w> basket = :[ apple banana ]
w> basket apple
true
w> basket pear
false