diff options
Diffstat (limited to 'src/clojure/contrib/types.clj')
| -rw-r--r-- | src/clojure/contrib/types.clj | 56 |
1 files changed, 44 insertions, 12 deletions
diff --git a/src/clojure/contrib/types.clj b/src/clojure/contrib/types.clj index 38f13cb2..53cdb816 100644 --- a/src/clojure/contrib/types.clj +++ b/src/clojure/contrib/types.clj @@ -1,7 +1,7 @@ -;; Algebraic data types +;; Data types ;; by Konrad Hinsen -;; last updated February 26, 2009 +;; last updated March 12, 2009 ;; Copyright (c) Konrad Hinsen, 2009. All rights reserved. The use ;; and distribution terms for this software are covered by the Eclipse @@ -12,11 +12,46 @@ ;; remove this notice, or any other, from this software. (ns clojure.contrib.types - "Algebraic data types") + "General and algebraic data types + + NOTE: This library is experimental. It may change significantly + with future release.") + +; +; Data type definition +; +(defmulti deconstruct type) +(defmethod deconstruct :default [x] (list x)) + +(defmacro deftype + "Define a data type by a type tag (a namespace-qualified keyword) + and a symbol naming the constructor function. Optionally, a pair + of constructor and deconstructor functions can be given as well, + the defaults are clojure.core/identity and clojure.core/list. + The full constructor associated with constructor-name calls the + constructor function and attaches the type tag to its result + as metadata. The deconstructor function must return the arguments + to be passed to the constructor in order to create an equivalent + object. It is used for printing and matching." + ([type-tag constructor-name] + `(deftype ~type-tag ~constructor-name identity list)) + ([type-tag constructor-name constructor deconstructor] + `(do + (derive ~type-tag ::type) + (let [meta-map# {:type ~type-tag ::constructor (quote ~constructor-name)}] + (def ~constructor-name + (comp (fn [~'x] (with-meta ~'x meta-map#)) ~constructor)) + (defmethod deconstruct ~type-tag [~'x] + (~deconstructor (with-meta ~'x {}))))))) + +(defmethod print-method ::type [o w] + (print-method (cons (::constructor ^o) (deconstruct o)) w)) ; ; Defining algebraic types ; +(derive ::adt ::type) + (defn- qualified-symbol [s] (symbol (str *ns*) (str s))) @@ -38,15 +73,13 @@ (with-meta [(quote ~(qualified-symbol name)) ~@args] ~meta-map-symbol)))))) -(defmacro deftype - "Define the algebraic data type name by an exhaustive list of constructors. +(defmacro defadt + "Define an algebraic data type name by an exhaustive list of constructors. Each constructor can be a symbol (argument-free constructor) or a list consisting of a tag symbol followed by the argument symbols. - The data type itself is a keyword declared as deriving from - :clojure.contrib.types/adt." - [name & constructors] - (let [type-tag (qualified-keyword name) - meta-map-symbol (gensym "mm") + The data type tag must be a keyword." + [type-tag & constructors] + (let [meta-map-symbol (gensym "mm") accessor1 (if (and (= 1 (count constructors)) (seq? (first constructors)) (= 2 (count (first constructors)))) @@ -60,7 +93,6 @@ nil)] `(let [~meta-map-symbol {:type ~type-tag}] (derive ~type-tag ::adt) - (def ~name ~type-tag) ~@(map (partial constructor-code meta-map-symbol) constructors) ~accessor1 ~accessor2 @@ -72,7 +104,7 @@ (defn- unqualified-symbol [s] (let [s-str (str s)] - (symbol (.substring s-str (inc (.indexOf s-str (int \/))))))) + (symbol (subs s-str (inc (.indexOf s-str (int \/))))))) (defmethod print-method ::adt [o w] (if (symbol? o) |