chickadee » srfi-209 » make-enum-type

Returns a newly allocated enum type containing a fixed set of newly allocated enums. Both enums and enum types are immutable, and it is not possible to create an enum except as part of creating an enum type.

The elements of list are either symbols or two-element lists, where each list has a symbol as the first element and any value as the second element. Each list element causes a single enum to be generated, and the enum's name is specified by the symbol. It is an error unless all the symbols are distinct within an enum type. The position of the element in list is the ordinal of the corresponding enum, so ordinals within an enum type are also distinct. If a value is given, it becomes the value of the enum; otherwise the enum’s value is the same as the ordinal.

define-enum should be preferred to make-enum-set. It generates efficient accessors and set constructors and can catch errors at expansion time.

The following example enum types will be used in examples throughout this SRFI, with the identifier type-name referring to the enum of type type with name name.

(define color
  (make-enum-type '(red orange yellow green cyan blue violet)))

(define us-traffic-light
  (make-enum-type '(red yellow green)))

(define pizza
  (make-enum-type '((margherita "tomato and mozzarella")
                    (funghi "mushrooms")
                    (chicago "deep-dish")
                    (hawaiian "pineapple and ham"))))