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3.2 Disjointness of types

No object satisfies more than one of the following predicates:

• boolean?
• bytevector?
• char?
• eof-object?
• null?
• number?
• pair?
• port?
• procedure?
• string?
• symbol?
• vector?

and all predicates created by define-record-type.

These predicates define the types boolean, bytevector, character, the empty list object, eof-object, number, pair, port, procedure, string, symbol, vector, and all record types.

Although there is a separate boolean type, any Scheme value can be used as a boolean value for the purpose of a conditional test. As explained in Booleans, all values count as true in such a test except for #f. This report uses the word “true” to refer to any Scheme value except #f, and the word “false” to refer to #f.