Protocols, records and enums

A protocol defines operations on implementing types. impl supplies methods; dyn packages a value for dynamic protocol dispatch. defstruct supplies fields, defenum supplies alternatives and match inspects them. defrecord is a library macro, not a core form. derive supplies supported library implementations; it does not implement arbitrary protocols. The coherence and orphan rules in types §2.9 constrain where implementations can be declared. Start with static dispatch:

(ns main)
(defprotocol Measure (measure (self) -> i64))
(defstruct Box (value: i64))
(impl Measure Box (measure (self) (. self value)))
(defun main () -> i64 (do (println (measure (Box 7))) 0))

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