Clojure Interoperability

INTEROPERABILITY
CLOJURE PYTHON
Enrico Franchi

2

OUTLINE

Why Clojure? Why Java?
Clojure from 3000 m.
Jython-Clojure interoperability
Clojure-Jython interoperability

ENRICO FRANCHI <EFRANCHI@CE.UNIPR.IT>

3

GENERAL NOTES

During this presentation some very explicit Java code may be shown.

No ducks were harmed during the making of this presentation.


4

JVM LANGUAGES

Jython Java ?

JVM


5

JVM LANGUAGES

Jython Java Clojure

JVM


6

CLOJURE

Clojure is Lisp
Clojure is a good Lisp

Clojure has a more functional flavor than Common Lisp;
stateful programming is banned unless in very controlled ways

Clojure lives on the JVM and perhaps its rejection of state
is a reaction to the heavily stateful model of JVM

Clojure is not a pure functional language by any means


7

JVM LANGUAGES

Jython
Implementation of Python in Java
Jython calls Java

~
Clojure
New Programming Languages built on the JVM
Design choices in Clojure reflect design choices of the JVM
Interoperability


8

CLOJURE

~ Good Parts ~

Functional Programming
Laziness
Full Macros
Multi-Methods
Immutable types, STM & Concurrency Model

~ Bad Parts ~

“Java”


9

ATOMIC TYPES

Integers
Floating Point Numbers
Ratios (3/4 is not 0.75, is ¾)
BigDecimal
Strings (“foo”)
Booleans (true, false)
Nil (nil)
Characters (a, b)
:keywords
regexp’s (#“foo.*”)


10

SEQUENCE TYPES

Python Common Lisp Clojure
Type Syntax Type Syntax Type Syntax
Random access list [1, 2] vector #(1 2) vector [1 2]
sequence
Linked List - No list (1 2) list (1 2)
Set set {1, 2} No No set #{1 2}
Map dict {1:2, 3:4} hash-table No vector {1 2, 3 4}

Clojure collections
In Clojure all collections are immutable;
implement corresponding
all the functions return a new collections – as usual,
Java collections interfaces
immutability allows easy data sharing –
vector, list List
set Set
map Map

11

CLOJURE EXAMPLE

(defn rember [a lat]
  (cond
   (empty? lat) '()
   (= (first lat) a) (rest lat)
   :else (cons
          (first lat)
          (rember a (rest lat)))))

(rember 4 '(1 2 3 4 5 6 4))
; => (1 2 3 5 6 4)

12

TAIL CALL OPTIMIZATION

(defn multirember [a lat]
  (letfn
      [(multirember-aux [source sink]
                   (if (seq source)
                     (if (= (first source) a)
                       (recur (rest source) sink)
                       (recur (rest source)
                              (conj sink (first source))))
                     sink))]
    (multirember-aux lat [])))
(take 10
(multirember 4 '(1 2 3 4 5 6 4)) (multirember 4 (iterate inc 0)))
; => [1 2 3 5 6] ; Evaluation aborted.

13

LAZINESS

(defn lazy-multirember [a lat]
  (letfn
      [(multirember-aux [source]
                        (lazy-seq
                         (if (seq source)
                             (multirember-aux (rest source))
                             (cons (first source)
                                   (multirember-aux (rest source))))
                          '())))]
    (multirember-aux lat)))

(take 10 (lazy-multirember 4 (iterate inc 0)))
; => (0 1 2 3 5 6 7 8 9 10)

14

NAMESPACES & MODULES

(ns example.namespace) (ns example.namespace
(:require clojure.set))
Introduces a new namespace.
With def (and defn, …) stuff is (ns example.namespace
added to namespaces. (:require [clojure.set :as s]))

(ns example.namespace (ns example.namespace
(:use clojure.string)) (:import [java.util HashMap]))
(ns example.namespace
(:use [clojure.string :only [capitalize]]))
(:use [clojure.string :exclude [capitalize]])

15

CALLING JAVA

Java Clojure Jython
import app.model.Person; (import [app.model Person]) from app.model import
Person
new Person() (new Person) Person()
(Person.)
person.getFullName() (. getFullName person) person.getFullName()
(.getFullName person)
Locale.JAPAN (. Locale JAPAN) Locale.JAPAN
Locale/JAPAN
Integer.valueOf(“42”) (. Integer valueOf "42") java.lang.Integer.valueOf('42')
(Integer/valueOf “42”)


16

PROXIES
(ns gui-sample
  (:import [javax.swing JFrame JButton]
(gui-sample/build-gui
           [java.awt.event ActionListener]))
"Rock & Roll"
(defn build-gui [title message] "Hello, world!”)
  (let [frame (JFrame. title)
        button (JButton. "CLICK")]
    (.addActionListener button
                        (proxy [ActionListener] []
                          (actionPerformed [evt]
                                           (println message))))
    (.. frame getContentPane (add button))
    (.pack frame)
    (.setVisible frame true)
    frame))


17

PROXIES
(ns gui-sample

(defn build-gui [title message]
        button (JButton. "CLICK")
        px (proxy [ActionListener] []
                                           (println message)))]
    (.addActionListener button px)
    (.pack frame)
    (.setVisible frame true) px))

(update-proxy p {"actionPerformed" (fn [this evt] (println "foo!"))})


18

GEN-CLASS

(ns example.ClassExample
  (:gen-class
   :name example.ClassExample
   :extends Object
   :implements []
   :methods [
[foo [java.util.Collection] int]
             ^{:static true} [show [java.util.Collection] void]])
  (:import (java.util Collection)))


19

GEN-CLASS (2)

(defn show [coll] (defn -show [coll]
  (if (seq coll)   (show coll))
    (do
      (print (first coll)) (defn -foo [this coll]
      (recur (rest coll)))   (let [coll (seq coll)]
    (println "")))     (if coll (count coll) -1)))
>>> import example
>>> example.ClassExample.show([1, 2, 3])
123

>>> ce = example.ClassExample()
>>> ce.foo([1, 2, 3])
3

20

IMPLEMENTING PYOBJECTS
IN CLOJURE
import clj
(ns clj.ImmutableList
(:gen-class py_list = ['a', 'b', 'c']
:name clj.ImmutableList my_list = clj.ImmutableList(py_list)
:extends org.python.core.PyObject
:implements [clojure.lang.IPersistentList]
:state state
:init init
:constructors {[java.util.Collection], []})
(:import [org.python.core PyObject PyInteger Py]))

(defn -init [coll]
[[coll] (apply list coll)])

21

IN CLOJURE (2)

(defmacro delegate-to-state [sym] (defn -cons [this other]
`(defn ~(symbol (str "-" sym)) (cons (.state this) other))
[this#]
(~sym (.state this#)))) (defn -equiv [this other]
print(.state this) other))
(= my_list.peek()
(delegate-to-state peek) print my_list.pop()
(delegate-to-state pop) print my_list.count()
(delegate-to-state count) print my_list.empty()
(delegate-to-state empty) print my_list.seq()
(delegate-to-state seq) print my_list.cons('d')
print my_list.equiv(py_list)
print my_list.equiv(['a', 'b', 'c'])

22

print my_list[0]
IN CLOJURE (3)
print my_list[1]
print my_list[2]
(defn -__finditem__ [this index] print my_list[2.4]
(let [index (if (instance? Number index)
index try:
(Py/tojava index Number))] print my_list[3]
except IndexError, e:
(try
print e
(Py/java2py (nth (.state this) index)) try:
(catch IndexOutOfBoundsException e print my_list['a']
(throw (Py/IndexError (.toString e))))))) except TypeError, e:
print e

try:
my_list[0] = 1
except TypeError, e:
print e

23

CLOJURE RT

from clojure.lang import RT, Compiler
source = '''
(ns rember) Compiler.load(java.io.StringReader(source))
(defn rember [a lat] rember = RT.var('rember', 'rember')
(cond print rember.invoke(2, range(4))
(empty? lat) '()
:else (cons
(first lat)
'''

24

CLOJURE DECORATOR
import pyclj

@pyclj.clojure
def rember(a, lat):
    ’’’(defn rember
"Remove first occurrence of a from lat"
[a lat] (cond
(empty? lat) '()
:else (cons (first lat)
(rember a (rest lat)))))’’’

if __name__ == '__main__':
    print rember(2, range(4))
    help(rember) ENRICO FRANCHI <EFRANCHI@CE.UNIPR.IT>

25

IMPLEMENTATION

def clojure(fn):
    """Decorator that substitutes an empty python function with clojure
in the doc with a callable which delegates to the clojure function.
"""
    clj_namespace = determine_clojure_namespace(fn)
    clojure_fnc = build_clojure_function_object(clj_namespace, fn)

    fn.__doc__ = get_docs(clojure_fnc)

    def aux(*args):
        return clojure_fnc.invoke(*args)
    functools.update_wrapper(aux, fn)

    return aux ENRICO FRANCHI <EFRANCHI@CE.UNIPR.IT>

26

IMPLEMENTATION (2)

def determine_clojure_namespace(fn):
    try:
        clj_namespace = fn.__module__
    except AttributeError:
        clj_namespace = 'user'
    return clj_namespace

def get_docs(clojure_fnc):
    meta = clojure_fnc.meta()
    return meta.get(Keyword.intern('doc'))


27

IMPLEMENTATION (3)

def build_clojure_function_object(clj_namespace, fn):
    clojure_code = '(ns %s)n%s' % (
        clj_namespace,
        fn.__doc__)
    clojure_compile_string(clojure_code)
    clojure_fnc = RT.var(clj_namespace, fn.func_name)
    return clojure_fnc


28

CALLING JYTHON FROM CLOJURE

(defn make-factory [modulename klassname]
  (let [interpreter (PythonInterpreter.)
class SpamAndEggs(object):
         import-command (str-join " " ["from" modulename
    def __init__(self, eggs):
"import" klassname])]
        self.eggs = eggs
    (.exec interpreter import-command)
    (.get interpreter klassname))) hasSpam(self):
    def
        return True
(def spam-and-eggs (make-factory "example" "SpamAndEggs"))
    def getEggs(self):
(def inst (.__call__ spam-and-eggs (Py/java2py 1)))
        return self.eggs

(println inst)     def __repr__(self):
(println (.invoke inst "hasSpam"))
        return 'Spam and %s eggs.' % self.eggs

29

(PT. 2)
(defn make-factory
  [module klassname]
        import-command (str-join " " ["from" module
    (let [klass (.get interpreter klassname)]
      (fn [& args]
        (.__call__ klass
          (into-array PyObject
            (map #(Py/java2py %) args)))))))

(def inst (spam-and-eggs 1))

30

THROW MACROS IN

(defmacro pyclass [q-class jtype]
  (let [[klass-name module-name] (split-module-and-class q-class)]
    `(def ~(symbol klass-name)
      (make-factory ~(str module-name) ~(str klass-name) ~jtype))))

(pyclass example.PrintSomething java.awt.event.ActionListener)

(def evt-printer (PrintSomething))


31

MAKE-FACTORY (AGAIN)

(defn make-factory
[module klassname interface]
import-command (str-join " " ["from" module "import" klassname])]
(fn [& args]
(.__tojava__ (.__call__ klass
(map #(Py/java2py %) args)))
interface)))))

32

BACK TO THE BEGINNING

(defn build-gui [title]
    (.addActionListener button (PrintSomething))
    (.pack frame)
    frame))


33

CONCLUSION

Thanks for Your Kind Attention

https://github.com/rik0/PyCLJ_Examples
https://github.com/rik0/pyclj


35

OUTLINE

Why Clojure? Why Java?
Clojure from 3000 m.
Jython-Clojure interoperability
Clojure-Jython interoperability


36

GENERAL NOTES




37

GENERAL NOTES




38

JVM LANGUAGES

Jython Java ?

JVM


39

JVM LANGUAGES

Jython Java Clojure

JVM


40

CLOJURE

Clojure is Lisp
Clojure is a good Lisp

Clojure has a more functional flavor than Common Lisp;
stateful programming is banned unless in very controlled ways

Clojure lives on the JVM and perhaps its rejection of state
is a reaction to the heavily stateful model of JVM

Clojure is not a pure functional language by any means


41

JVM LANGUAGES

Jython
Implementation of Python in Java
Jython calls Java

~
Clojure
New Programming Languages built on the JVM
Design choices in Clojure reflect design choices of the JVM
Interoperability


42

CLOJURE

~ Good Parts ~

Functional Programming
Laziness
Full Macros
Multi-Methods
Immutable types, STM & Concurrency Model

~ Bad Parts ~

“Java”


43

ATOMIC TYPES

Integers
Floating Point Numbers
Ratios (3/4 is not 0.75, is ¾)
BigDecimal
Strings (“foo”)
Booleans (true, false)
Nil (nil)
Characters (a, b)
:keywords
regexp’s (#“foo.*”)


44

SEQUENCE TYPES

Python Common Lisp Clojure
Type Syntax Type Syntax Type Syntax
Random access list [1, 2] vector #(1 2) vector [1 2]
sequence
Linked List - No list (1 2) list (1 2)
Set set {1, 2} No No set #{1 2}
Map dict {1:2, 3:4} hash-table No vector {1 2, 3 4}

Clojure collections
In Clojure all collections are immutable;
implement corresponding
all the functions return a new collections – as usual,
Java collections interfaces
immutability allows easy data sharing –
vector, list List
set Set
map Map

45

CLOJURE EXAMPLE

(defn rember [a lat]
  (cond
   (empty? lat) '()
   :else (cons
          (first lat)

(rember 4 '(1 2 3 4 5 6 4))
; => (1 2 3 5 6 4)

46

TAIL CALL OPTIMIZATION

(defn multirember [a lat]
  (letfn
      [(multirember-aux [source sink]
                   (if (seq source)
                       (recur (rest source) sink)
                       (recur (rest source)
                              (conj sink (first source))))
                     sink))]
    (multirember-aux lat [])))
(take 10
(multirember 4 '(1 2 3 4 5 6 4)) (multirember 4 (iterate inc 0)))
; => [1 2 3 5 6] ; Evaluation aborted.

47

LAZINESS

(defn lazy-multirember [a lat]
  (letfn
      [(multirember-aux [source]
                        (lazy-seq
                         (if (seq source)
                             (multirember-aux (rest source))
                             (cons (first source)
                                   (multirember-aux (rest source))))
                          '())))]
    (multirember-aux lat)))

(take 10 (lazy-multirember 4 (iterate inc 0)))
; => (0 1 2 3 5 6 7 8 9 10)

48

NAMESPACES & MODULES

(ns example.namespace) (ns example.namespace
(:require clojure.set))
Introduces a new namespace.
With def (and defn, …) stuff is (ns example.namespace
added to namespaces. (:require [clojure.set :as s]))

(ns example.namespace (ns example.namespace
(:use clojure.string)) (:import [java.util HashMap]))
(:use [clojure.string :only [capitalize]]))
(:use [clojure.string :exclude [capitalize]])

49

CALLING JAVA

Java Clojure Jython
import app.model.Person; (import [app.model Person]) from app.model import
Person
new Person() (new Person) Person()
(Person.)
person.getFullName() (. getFullName person) person.getFullName()
(.getFullName person)
Locale.JAPAN (. Locale JAPAN) Locale.JAPAN
Locale/JAPAN
Integer.valueOf(“42”) (. Integer valueOf "42") java.lang.Integer.valueOf('42')
(Integer/valueOf “42”)


50

PROXIES
(ns gui-sample
(gui-sample/build-gui
"Rock & Roll"
(defn build-gui [title message] "Hello, world!”)
    (.addActionListener button
                        (proxy [ActionListener] []
                                           (println message))))
    (.pack frame)
    frame))


51

PROXIES
(ns gui-sample

(defn build-gui [title message]
        button (JButton. "CLICK")
        px (proxy [ActionListener] []
                                           (println message)))]
    (.addActionListener button px)
    (.pack frame)
    (.setVisible frame true) px))

(update-proxy p {"actionPerformed" (fn [this evt] (println "foo!"))})


52

GEN-CLASS

(ns example.ClassExample
  (:gen-class
   :name example.ClassExample
   :extends Object
   :implements []
   :methods [
[foo [java.util.Collection] int]
             ^{:static true} [show [java.util.Collection] void]])
  (:import (java.util Collection)))


53

GEN-CLASS (2)

(defn show [coll] (defn -show [coll]
  (if (seq coll)   (show coll))
    (do
      (print (first coll)) (defn -foo [this coll]
      (recur (rest coll)))   (let [coll (seq coll)]
    (println "")))     (if coll (count coll) -1)))
>>> import example
>>> example.ClassExample.show([1, 2, 3])
123

>>> ce = example.ClassExample()
>>> ce.foo([1, 2, 3])
3

54

IN CLOJURE

(:gen-class
:name clj.ImmutableList
:state state
:init init

(defn -init [coll]

55

IN CLOJURE
import clj
(:gen-class py_list = ['a', 'b', 'c']
:name clj.ImmutableList my_list = clj.ImmutableList(py_list)
:state state
:init init

(defn -init [coll]

56

IN CLOJURE (2)

[this#]
(= (.state this) other))
(delegate-to-state peek)
(delegate-to-state pop)
(delegate-to-state count)
(delegate-to-state empty)
(delegate-to-state seq)


57

IN CLOJURE (2)

[this#]
print(.state this) other))
(= my_list.peek()
(delegate-to-state peek) print my_list.pop()
(delegate-to-state pop) print my_list.count()
(delegate-to-state count) print my_list.empty()
(delegate-to-state empty) print my_list.seq()
(delegate-to-state seq) print my_list.cons('d')
print my_list.equiv(py_list)
print my_list.equiv(['a', 'b', 'c'])

58

print my_list[0]
IN CLOJURE (3)
print my_list[1]
print my_list[2]
(defn -__finditem__ [this index] print my_list[2.4]
(let [index (if (instance? Number index)
index try:
(Py/tojava index Number))] print my_list[3]
except IndexError, e:
(try
print e
(Py/java2py (nth (.state this) index)) try:
(catch IndexOutOfBoundsException e print my_list['a']
(throw (Py/IndexError (.toString e))))))) except TypeError, e:
print e

try:
my_list[0] = 1
except TypeError, e:
print e

59

CLOJURE RT

from clojure.lang import RT, Compiler
source = '''
(ns rember) Compiler.load(java.io.StringReader(source))
(defn rember [a lat] rember = RT.var('rember', 'rember')
(cond print rember.invoke(2, range(4))
(empty? lat) '()
:else (cons
(first lat)
'''

60

CLOJURE DECORATOR
import pyclj

@pyclj.clojure
def rember(a, lat):
    ’’’(defn rember
"Remove first occurrence of a from lat"
[a lat] (cond
(empty? lat) '()
:else (cons (first lat)
(rember a (rest lat)))))’’’

if __name__ == '__main__':
    print rember(2, range(4))
    help(rember) ENRICO FRANCHI <EFRANCHI@CE.UNIPR.IT>

61

IMPLEMENTATION

def clojure(fn):
    """Decorator that substitutes an empty python function with clojure
in the doc with a callable which delegates to the clojure function.
"""
    clj_namespace = determine_clojure_namespace(fn)
    clojure_fnc = build_clojure_function_object(clj_namespace, fn)

    fn.__doc__ = get_docs(clojure_fnc)

    def aux(*args):
        return clojure_fnc.invoke(*args)
    functools.update_wrapper(aux, fn)

    return aux ENRICO FRANCHI <EFRANCHI@CE.UNIPR.IT>

62

IMPLEMENTATION (2)

def determine_clojure_namespace(fn):
    try:
        clj_namespace = fn.__module__
    except AttributeError:
        clj_namespace = 'user'
    return clj_namespace

def get_docs(clojure_fnc):
    meta = clojure_fnc.meta()
    return meta.get(Keyword.intern('doc'))


63

IMPLEMENTATION (3)

def build_clojure_function_object(clj_namespace, fn):
    clojure_code = '(ns %s)n%s' % (
        clj_namespace,
        fn.__doc__)
    clojure_compile_string(clojure_code)
    clojure_fnc = RT.var(clj_namespace, fn.func_name)
    return clojure_fnc


64


    (.get interpreter klassname)))



(println inst)

65


class SpamAndEggs(object):
    def __init__(self, eggs):
        self.eggs = eggs
    (.get interpreter klassname))) hasSpam(self):
    def
        return True
    def getEggs(self):
        return self.eggs

(println inst)     def __repr__(self):
        return 'Spam and %s eggs.' % self.eggs

66

(PT. 2)
(defn make-factory
  [module klassname]
        import-command (str-join " " ["from" module
      (fn [& args]
        (.__call__ klass
            (map #(Py/java2py %) args)))))))

(def inst (spam-and-eggs 1))

67

THROW MACROS IN

(defmacro pyclass [q-class jtype]
  (let [[klass-name module-name] (split-module-and-class q-class)]
    `(def ~(symbol klass-name)
      (make-factory ~(str module-name) ~(str klass-name) ~jtype))))

(pyclass example.PrintSomething java.awt.event.ActionListener)

(def evt-printer (PrintSomething))


68

MAKE-FACTORY (AGAIN)

(defn make-factory
[module klassname interface]
import-command (str-join " " ["from" module "import" klassname])]
(fn [& args]
(.__tojava__ (.__call__ klass
(map #(Py/java2py %) args)))
interface)))))

69

BACK TO THE BEGINNING

(defn build-gui [title]
    (.addActionListener button (PrintSomething))
    (.pack frame)
    frame))


70

CONCLUSION

Thanks for Your Kind Attention

https://github.com/rik0/PyCLJ_Examples
https://github.com/rik0/pyclj


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