5.3 Defining Typedefs

Typedefs are similar to typedefs in C, except they are more like “type wrappers” than aliases, for reasons that will become clear in the next section.

Defining a typedef is as simple as giving defctype a new name and the name of the type to be wrapped. Here is how a simpler version of the built-in :boolean type could be defined:

  ;;; Define MY-BOOLEAN as an alias for the built-in type :INT.
  (defctype my-boolean :int)

With this type definition, one can declare arguments to foreign functions as having the type my-boolean, and they will be passed as integers. No conversion is taking place—if nil is passed as a my-boolean, a type error will be signalled.