define-class

define-class introduces a type class.

Syntax

(define-class (⟨constraints⟩ ... => ⟨class-name⟩ ⟨fields⟩ ... ⟨func-deps⟩?)
  (⟨method⟩ ⟨docstring⟩? ⟨type⟩)
  ...)

;; ⟨func-deps⟩ := (⟨type-var⟩ -> ⟨type-var⟩*)

Semantics

• The class head may include constraints and functional dependencies.
• Constraints in effect allow the definition of a subclass.
• Functional dependencies help the inferencer if one type variable completely determine the others.
• Methods are declared as part of the class definition.
• Instances are supplied separately with define-instance.
• If no methods are present, then it is called a “marker class”. They must still be instantiated, but only serve to mark a type.
• A docstring is optional.

Example

(define-class (Eq :a)
  (== "Mathematical equality." (:a * :a -> Boolean)))