Previous: lambda* Reference, Up: Optional Arguments

5.8.3.4 define* Reference

Just like define has a shorthand notation for defining procedures (see Lambda Alternatives), define* is provided as an abbreviation of the combination of define and lambda*.

define*-public is the lambda* version of define-public; defmacro* and defmacro*-public exist for defining macros with the improved argument list handling possibilities. The -public versions not only define the procedures/macros, but also export them from the current module.

— library syntax: define* formals body
— library syntax: define*-public formals body

define* and define*-public support optional arguments with a similar syntax to lambda*. They also support arbitrary-depth currying, just like Guile's define. Some examples: 

          (define* (x y #:optional a (z 3) #:key w . u)
             (display (list y z u)))

defines a procedure x with a fixed argument y, an optional argument a, another optional argument z with default value 3, a keyword argument w, and a rest argument u. 

          (define-public* ((foo #:optional bar) #:optional baz) '())

This illustrates currying. A procedure foo is defined, which, when called with an optional argument bar, returns a procedure that takes an optional argument baz.

Of course, define*[-public] also supports #:rest and #:allow-other-keys in the same way as lambda*.

— library syntax: defmacro* name formals body
— library syntax: defmacro*-public name formals body

These are just like defmacro and defmacro-public except that they take lambda*-style extended parameter lists, where #:optional, #:key, #:allow-other-keys and #:rest are allowed with the usual semantics. Here is an example of a macro with an optional argument: 

          (defmacro* transmorgify (a #:optional b)
              (a 1))