• Summary
• Acknowledgments
• Getting Started


• Overview of Scheme
• Lexical conventions
• Basic concepts
• Expressions
• Program structure
• Standard procedures


• Haskell Interface


• Standard Libraries
• Husk Libraries
• Standard Feature Identifiers
• Index

Booleans

The standard boolean objects for true and false are written as #t and #f. Alternatively, they can be written #true and #false, respectively. What really matters, though, are the objects that the Scheme conditional expressions ( if, cond, and, or, when, unless, do) treat as true or false. The phrase "a true value" (or sometimes just "true") means any object treated as true by the conditional expressions, and the phrase "a false value" (or "false") means any object treated as false by the conditional expressions.

Of all the Scheme values, only #f counts as false in conditional expressions. All other Scheme values, including #t, count as true.

Unlike some other dialects of Lisp, Scheme distinguishes #f and the empty list from each other and from the symbol nil.

Boolean constants evaluate to themselves, so they do not need to be quoted in programs.