Modify multimethods to use dispatching function

docs/contrib/multi.rst

@@ -4,20 +4,75 @@ defmulti
 
 .. versionadded:: 0.10.0
 
-``defmulti`` lets you arity-overload a function by the given number of
+``defmulti``, ``defmethod`` and ``default-method`` lets you define
-args and/or kwargs. Inspired by Clojure's take on ``defn``.
+multimethods where a dispatching function is used to select between different
+implementations of the function. Inspired by Clojure's multimethod and based
+on the code by `Adam Bard`_.
 
 .. code-block:: clj
 
     => (require hy.contrib.multi)
-    =>   (defmulti fun
+    => (defmulti area [shape]
-    ...     ([a] "a")
+    ...  "calculate area of a shape"
-    ...     ([a b] "a b")
+    ...  (:type shape))
-    ...     ([a b c] "a b c"))
+  
-    => (fun 1)
+    => (defmethod area "square" [square]
-    "a"
+    ...  (* (:width square)
-    => (fun 1 2)
+    ...     (:height square)))
-    "a b"
+  
-    => (fun 1 2 3)
+    => (defmethod area "circle" [circle]
-    "a b c"
+    ...  (* (** (:radius circle) 2) 
+    ...     3.14))
 
+    => (default-method area [shape]
+    ...  0)
+
+    => (area {:type "circle" :radius 0.5})
+    0.785
+
+    => (area {:type "square" :width 2 :height 2})
+    4
+
+    => (area {:type "non-euclid rhomboid"})
+    0
+
+``defmulti`` is used to define the initial multimethod with name, signature
+and code that selects between different implementations. In the example,
+multimethod expects a single input that is type of dictionary and contains
+at least key :type. The value that corresponds to this key is returned and
+is used to selected between different implementations.
+
+``defmethod`` defines a possible implementation for multimethod. It works
+otherwise in the same way as ``defn``, but has an extra parameters 
+for specifying multimethod and which calls are routed to this specific
+implementation. In the example, shapes with "square" as :type are routed to
+first function and shapes with "circle" as :type are routed to second
+function.
+
+``default-method`` specifies default implementation for multimethod that is
+called when no other implementation matches.
+
+Interfaces of multimethod and different implementation don't have to be
+exactly identical, as long as they're compatible enough. In practice this
+means that multimethod should accept the broadest range of parameters and
+different implementations can narrow them down.
+
+.. code-block:: clj
+
+    => (require hy.contrib.multi)
+    => (defmulti fun [&rest args]
+    ...  (len args))
+
+    => (defmethod fun 1 [a]
+    ...  a)
+
+    => (defmethod fun 2 [a b]
+    ...  (+ a b))
+
+    => (fun 1)
+    1
+
+    => (fun 1 2)
+    3
+
+.. _Adam Bard: https://adambard.com/blog/implementing-multimethods-in-python/

hy/contrib/dispatch/__init__.py

@@ -1,50 +0,0 @@
-# -*- encoding: utf-8 -*-
-#
-# Decorator for defmulti
-#
-# Copyright (c) 2014 Morten Linderud <mcfoxax@gmail.com>
-#
-# Permission is hereby granted, free of charge, to any person obtaining a
-# copy of this software and associated documentation files (the "Software"),
-# to deal in the Software without restriction, including without limitation
-# the rights to use, copy, modify, merge, publish, distribute, sublicense,
-# and/or sell copies of the Software, and to permit persons to whom the
-# Software is furnished to do so, subject to the following conditions:
-#
-# The above copyright notice and this permission notice shall be included in
-# all copies or substantial portions of the Software.
-#
-# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
-# THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
-# DEALINGS IN THE SOFTWARE.
-
-from collections import defaultdict
-
-
-class MultiDispatch(object):
-    _fns = defaultdict(dict)
-
-    def __init__(self, fn):
-        self.fn = fn
-        self.__doc__ = fn.__doc__
-        if fn.__name__ not in self._fns[fn.__module__].keys():
-            self._fns[fn.__module__][fn.__name__] = {}
-        values = fn.__code__.co_varnames
-        self._fns[fn.__module__][fn.__name__][values] = fn
-
-    def is_fn(self, v, args, kwargs):
-        """Compare the given (checked fn) too the called fn"""
-        com = list(args) + list(kwargs.keys())
-        if len(com) == len(v):
-            return all([kw in com for kw in kwargs.keys()])
-        return False
-
-    def __call__(self, *args, **kwargs):
-        for i, fn in self._fns[self.fn.__module__][self.fn.__name__].items():
-            if self.is_fn(i, args, kwargs):
-                return fn(*args, **kwargs)
-        raise TypeError("No matching functions with this signature!")

hy/contrib/multi.hy

@@ -1,5 +1,6 @@
 ;; Hy Arity-overloading
 ;; Copyright (c) 2014 Morten Linderud <mcfoxax@gmail.com>
+;; Copyright (c) 2016 Tuukka Turto <tuukka.turto@oktaeder.net>
 
 ;; Permission is hereby granted, free of charge, to any person obtaining a
 ;; copy of this software and associated documentation files (the "Software"),
@@ -19,23 +20,37 @@
 ;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 ;; DEALINGS IN THE SOFTWARE.
 
-(import [collections [defaultdict]])
+(defn multi-decorator [dispatch-fn]
-(import [hy.models.string [HyString]])
+  (setv inner (fn [&rest args &kwargs kwargs]
+                (setv dispatch-key (apply dispatch-fn args kwargs))
+                (if (in dispatch-key inner.--multi--)
+                  (apply (get inner.--multi-- dispatch-key) args kwargs)
+                  (apply inner.--multi-default-- args kwargs))))
+  (setv inner.--multi-- {})
+  (setv inner.--doc-- dispatch-fn.--doc--)
+  (setv inner.--multi-default-- (fn [&rest args &kwargs kwargs] nil))
+  inner)
 
-
+(defn method-decorator [dispatch-fn &optional [dispatch-key nil]]
-(defmacro defmulti [name &rest bodies]
+  (setv apply-decorator
-  (def comment (HyString))
+        (fn [func]
-  (if (= (type (first bodies)) HyString)
+          (if (is dispatch-key nil)
-    (do (def comment (car bodies))
+            (setv dispatch-fn.--multi-default-- func)
-        (def bodies (cdr bodies))))
+           (assoc dispatch-fn.--multi-- dispatch-key func))
-
+          dispatch-fn))
-  (def ret `(do))
+  apply-decorator)
-  
-  (.append ret '(import [hy.contrib.dispatch [MultiDispatch]]))
  
-  (for [body bodies]
+(defmacro defmulti [name params &rest body]
-    (def let-binds (car body))
+  `(do (import [hy.contrib.multi [multi-decorator]])
-    (def body (cdr body))
+       (with-decorator multi-decorator
-    (.append ret 
+         (defn ~name ~params ~@body))))
-        `(with-decorator MultiDispatch (defn ~name ~let-binds ~comment ~@body))))
+
-  ret)
+(defmacro defmethod [name multi-key params &rest body]
+  `(do (import [hy.contrib.multi [method-decorator]])
+       (with-decorator (method-decorator ~name ~multi-key)
+         (defn ~name ~params ~@body))))
+
+(defmacro default-method [name params &rest body]
+  `(do (import [hy.contrib.multi [method-decorator]])
+       (with-decorator (method-decorator ~name)
+         (defn ~name ~params ~@body))))

tests/native_tests/contrib/multi.hy

@@ -1,4 +1,5 @@
 ;; Copyright (c) 2014 Morten Linderud <mcfoxax@gmail.com>
+;; Copyright (c) 2016 Tuukka Turto <tuukka.turto@oktaeder.net>
  
 ;; Permission is hereby granted, free of charge, to any person obtaining a
 ;; copy of this software and associated documentation files (the "Software"),
@@ -21,13 +22,22 @@
 (require hy.contrib.multi)
 
 
-(defn test-basic-multi []
+(defn test-different-signatures []
-  "NATIVE: Test a basic defmulti"
+  "NATIVE: Test multimethods with different signatures"
-  (defmulti fun
+  (defmulti fun [&rest args]
-    ([] "Hello!")
+    (len args))
-    ([a] a)
+
-    ([a b] "a b")
+  (defmethod fun 0 []
-    ([a b c] "a b c"))
+    "Hello!")
+
+  (defmethod fun 1 [a]
+    a)
+
+  (defmethod fun 2 [a b]
+    "a b")
+
+  (defmethod fun 3 [a b c]
+    "a b c")
 
   (assert (= (fun) "Hello!"))
   (assert (= (fun "a") "a"))
@@ -35,23 +45,49 @@
   (assert (= (fun "a" "b" "c") "a b c")))
 
 
-(defn test-kw-args []
+(defn test-basic-dispatch []
-  "NATIVE: Test if kwargs are handled correctly"
+  "NATIVE: Test basic dispatch"
-  (defmulti fun
+  (defmulti area [shape]
-    ([a] a)
+    (:type shape))
-    ([&optional [a "nop"] [b "p"]] (+ a b)))
+  
-   
+  (defmethod area "square" [square]
-  (assert (= (fun 1) 1))
+    (* (:width square)
-  (assert (= (apply fun [] {"a" "t"}) "t"))
+       (:height square)))
-  (assert (= (apply fun ["hello "] {"b" "world"}) "hello world"))
+  
-  (assert (= (apply fun [] {"a" "hello " "b" "world"}) "hello world")))
+  (defmethod area "circle" [circle]
+    (* (** (:radius circle) 2) 
+       3.14))
 
+  (default-method area [shape]
+    0)
+
+  (assert (< 0.784 (area {:type "circle" :radius 0.5}) 0.786))
+  (assert (= (area {:type "square" :width 2 :height 2})) 4)
+  (assert (= (area {:type "non-euclid rhomboid"}) 0)))
 
 (defn test-docs []
   "NATIVE: Test if docs are properly handled"
-  (defmulti fun
+  (defmulti fun [a b]
     "docs"
-    ([a] (print a))
+    a)
-    ([a b] (print b)))
+
+  (defmethod fun "foo" [a b]
+    "foo was called")
+
+  (defmethod fun "bar" [a b]
+    "bar was called")
   
   (assert (= fun.--doc-- "docs")))
+
+(defn test-kwargs-handling []
+  "NATIVE: Test handling of kwargs with multimethods"
+  (defmulti fun [&kwargs kwargs]
+    (get kwargs "type"))
+
+  (defmethod fun "foo" [&kwargs kwargs]
+    "foo was called")
+
+  (defmethod fun "bar" [&kwargs kwargs]
+    "bar was called")
+
+  (assert (= (fun :type "foo" :extra "extra") "foo was called")))