The document provides an agenda for a Clojure Deep Dive presentation. The agenda includes sections on the Core Language, Standard Tools, Clojure Compilation, and Clojure Pitfalls. It then goes on to describe various aspects of the Clojure core language such as forms, functions, namespaces, and more.

1. Clojure Deep
Dive
Howard M. Lewis Ship
TWD Consulting
hlship@gmail.com
1 © 2009 Howard Lewis Ship

2. Agenda
• Core Language
• Standard Tools
• Clojure Compilation
• Clojure Pitfalls
2 © 2009 Howard Lewis Ship

3. Core Language
3 © 2009 Howard Lewis Ship

4. What's A Form?
Constants: Keywords: Symbols:
42 :foo map
"hello" :tag strutils2/take
Data Structures:
[…]
{…}
#{ … }
Callables:
Special Forms: Function Call: Macros Expansion:
(if …) (map …) (and …)
(var …) (or …)
(do …) (ns …)
4 © 2009 Howard Lewis Ship

5. defn: Define a function
Symbol (in current namespace)
Optional doc string
(defn to-seq
"Converts the object to a sequence (a vector)
unless it is already sequential."
[obj]
(if (sequential? obj) obj [obj]))
List of parameters
user=> (doc to-seq)
-------------------------
user/to-seq
([obj])
Converts the object to a sequence (a vector)
unless it is already sequential.
nil
user=>
5 © 2009 Howard Lewis Ship

6. defn: Multiple Arities
One doc string
Series of argument lists / forms
(defn not=
"Same as (not (= obj1 obj2))"
([x] false)
([x y] (not (= x y)))
([x y & more]
(not (apply = x y more))))
& symbol ➠ provide
remaining values as a
seq
user=> (doc not=)
-------------------------
clojure.core/not=
([x] [x y] [x y & more])
Same as (not (= obj1 obj2))
nil
user=>
6 © 2009 Howard Lewis Ship

7. let: local symbols
(let [center (calc-center-for-frame frame)
x (get-x center)
y (get-y center)]
…)
•Even number: symbol1 form1 symbol2 form2 …
•Not variables: symbols are read-only
•Can re-define symbols
7 © 2009 Howard Lewis Ship

8. do: evaluate for side-effects
(if value-found
(do
(println "Found the value.")
value-found))
Last form is the result
; Broken
(if value-found
(println "Found the value.") If true, side effect & return nil
value-found)
If false, return value (false or nil)
8 © 2009 Howard Lewis Ship

9. Branching: if, when
(if test then-form)
(if test then-form else-form)
• Special form: not a function
• Evaluates test, then evaluates & returns either then-form or
else-form
• false and nil ➠ logical false
• anything else ➠ logical true
(when test then-forms) (if-not test then-form)
(if-not test then-form else-form)
Any number of forms in an
implicit do Like (if (not test) then else)
(when-not test then-forms)
9 © 2009 Howard Lewis Ship

10. if-let, when-let
(if-let [symbol test] then-form)
(if-let [symbol test] then-form else-form)
Symbol can be referenced
(when-let [symbol test] then-forms)
Any number of forms in an
implicit do
10 © 2009 Howard Lewis Ship

11. or, and
(or form…)
(and form…)
• or: first value from list that evaluates to true
• Will return value of last expression (false or nil)
• (or) returns nil
• and: first logical false (nil or false)
• Returns value of last expression (if prior are logical true)
• (and) return true
• Can be used as a "guard" Only invoke symbol and find-ns
(defn dispatch-named-function-to-pipeline if ns-name is non-nil
[env pipeline]
(let [split-path (-> env :cascade :split-path)
[_ ns-name fn-name] split-path
fn-namespace (and ns-name (find-ns (symbol ns-name)))
named-function (and fn-namespace fn-name (ns-resolve fn-namespace (symbol fn-name)))
new-env (assoc-in env [:cascade :extra-path] (drop 3 split-path))]
(call-pipeline pipeline new-env named-function)))
11 © 2009 Howard Lewis Ship

12. Destructuring
Bu
N wo
sy
o rk
• Automatically extract values from data structures
!
• Binding forms:
• Map to extract keys
• Vector to extract indexed values
• Function parameters
One un-named parameter
• let, if-let, when-let, etc. destructured to two symbols
user=> (defn natural-name
[{fname :first-name lname :last-name}]
(str lname ", " fname))
#'user/natural-name
user=> (natural-name (persons 1))
"Simon, Scott"
user=>
12 © 2009 Howard Lewis Ship

13. Destructuring
• Binding Forms:
• symbol (let [x (get-x center)] … )
• vector of binding forms (let [[x y] center] … )
• map of binding form to map key
(let [{fname :first-name lname :last-name} person] …)
13 © 2009 Howard Lewis Ship

14. Vector Destructuring
center must be sequential
(let [[x y] center] …)
May be nil if not enough values in center
(let [[first-born second-born & other-children] children] …)
& symbol gets the remaining values
(let [[first-born second-born & other-children :as children] (find-children parent)] …)
Nested binding forms! :as symbol gets the full list
user=> (let [[[x1 y1][x2 y2]] [[1 2] [3 4]]]
[x1 y1 x2 y2])
[1 2 3 4]
user=>
14 © 2009 Howard Lewis Ship

15. Map Destructuring
(defn natural-name [{fname :first-name lname :last-name}] (str lname ", " fname))
(defn natural-name [{:keys [first-name last-name]}] (str last-name ", " first-name))
:keys maps a keyword key for each symbol
:or sets defaults for missing keys
user=> (defn natural-name [{:keys [first-name last-name]
:or {first-name "(none)" last-name "(none)"}}]
(str last-name ", " first-name))
#'user/natural-name
user=> (natural-name {:first-name "Gromit"})
"(none), Gromit"
user=> (natural-name {:first-name "Gromit" :last-name nil})
", Gromit"
user=>
:as symbol to get the original map
:strs ➠ like :keys, but maps to string keys, not keyword keys
:syms ➠ like :keys, but maps to symbol keys, not keyword keys
15 © 2009 Howard Lewis Ship

16. ns: define namespaces
(ns example.utils)
cascade/dispatcher.clj
(ns cascade.dispatcher
(:import (javax.servlet ServletResponse))
File: example/utils.clj (:use (cascade config dom logging path-map pipeline)
(cascade.internal utils)))
(ns namespace
(:import …) Optional directives
(:use …))
user=> (defn natural-name
[{fname :first-name lname :last-name}]
(str lname ", " fname))
#'user/natural-name
user=> (natural-name (persons 1))
"Simon, Scott"
user=>
user/natural-name
Namespace: user
Symbol: natural-name
16 © 2009 Howard Lewis Ship

17. :import Java Classes
Package name, then any number of classes/interfaces
(ns cascade.dispatcher
(:import (javax.servlet ServletResponse))
…)
Repeat for other packages
Can also list fully qualify class names
17 © 2009 Howard Lewis Ship

18. :use Import Namespaces
(:use clojure.contrib.pprint)
Symbols defined by pprint are available, i.e.
(pprint [1 2 3])
(:use (clojure.contrib pprint monads))
Add multiple namespaces under the root
namespace
(:use (clojure.contrib (str-utils2 :only [join map-str]))
Uses just join and map-str from str-utils2
(:use (clojure.contrib (str-utils2 :exclude [take replace drop]))
Exclude just some of the symbols
(:use (clojure.contrib (str-utils2 :rename {take strtake}))
Use str-utils2, mapping take as strtake
18 © 2009 Howard Lewis Ship

19. Other ns directives
• :require ➠ load a namespace but don't import it
• :gen-class ➠ create a Java class from functions in the
namespace
• :refer-clojure ➠ import selected clojure.core symbols
• :load ➠ load Clojure scripts (not namespaces)
19 © 2009 Howard Lewis Ship

20. Standard
Tools
20 © 2009 Howard Lewis Ship

21. Anonymous Functions
#() ➠ implicit anonymous function
(filter #(not (.startsWith % ".")) names)
% is replaced by the function's parameter
%n is parameter #n
(map
#(assoc %1 :sort-index %2)
(sort-by :age persons)
(iterate inc 0))
inline anonymous function
(map
21
(fn [person-map sort-index]
(assoc person-map :sort-index sort-index))
(sort-by :age persons)
(iterate inc 0))
© 2009 Howard Lewis Ship

22. What are seqs?
Seqable
seq() : ISeq
IPersistentCollection Sequential
count() : int
cons(Object): IPersistentCollection
empty() : IPersistentCollection
equiv(Object) : boolean
PersistentSet ISeq
first() : Object
next(): ISeq
more(): ISeq
cons(Object): ISeq Returned from map, for,
filter, remove, etc.
PersistentList PersistentVector LazySeq
22 © 2009 Howard Lewis Ship

23. assoc-in / update-in
user=> (def person { :first-name "Howard" :last-name "Lewis Ship"
:address { :street "123 NW 12th Ave. #541" :city "Portland" :state "OR" :zip 97309 }})
#'user/person
user=> (assoc-in person [:address :street] "2647 SE 97th Ave.")
{:first-name "Howard", :last-name "Lewis Ship",
:address {:street "2647 SE 97th Ave.", :city "Portland", :state "OR", :zip 97309}}
user=> (update-in person [:address :zip] + 5)
{:first-name "Howard", :last-name "Lewis Ship",
:address {:street "123 NW 12th Ave. #541", :city "Portland", :state "OR", :zip 97314}}
user=>
:first-name "Howard"
:last-name "Lewis Ship"
:address :street "123 NW 12th Ave."
:city "Portland"
:state "OR"
:zip 97309
(update-in person [:address :zip] + 5)
(+ 97309 5)
:first-name "Howard"
:last-name "Lewis Ship"
:address :street "123 NW 12th Ave."
:city "Portland"
:state "OR"
:zip 97314
23 © 2009 Howard Lewis Ship

24. map
La
zy
f
:age acts as a function
user=> (map :age persons)
(42 44 29)
user=> (map #(apply str (reverse (% :first-name))) persons)
("drawoH" "ttocS" "ylloM")
user=> (map identity (persons 0))
([:first-name "Howard"] iterate a map ➠ key/value pairs
[:last-name "Lewis Ship"]
[:age 42])
user=> (seq (persons 0))
([:first-name "Howard"]
[:last-name "Lewis Ship"]
[:age 42])
user=>
24 © 2009 Howard Lewis Ship

25. map
La
zy
f
N seqs ➠ N parameters
user=> (map #(assoc %1 :sort-index %2)
(sort-by :age persons)
(iterate inc 0))
({:sort-index 0, :first-name "Molly", :last-name "Newman", :age 29}
{:sort-index 1, :first-name "Howard", :last-name "Lewis Ship", :age 42}
{:sort-index 2, :first-name "Scott", :last-name "Simon", :age 44})
user=>
25 © 2009 Howard Lewis Ship

26. reduce
f
user=> (map :age persons)
(42 44 29 38)
user=> (reduce + (map :age persons))
153
(reduce + (map :age persons))
26 © 2009 Howard Lewis Ship

27. reduce
f
user=> (map :age persons)
(42 44 29 38)
user=> (reduce + (map :age persons))
153
(reduce + (map :age persons))
(reduce + '(42 44 29 38))
27 © 2009 Howard Lewis Ship

28. reduce
f
user=> (map :age persons)
(42 44 29 38)
user=> (reduce + (map :age persons))
153
(reduce + (map :age persons))
(reduce + '(42 44 29 38))
(+ (+ (+ 42 44) 29) 38)
28 © 2009 Howard Lewis Ship

29. reduce
f
user=> (map :age persons)
(42 44 29 38)
user=> (reduce + (map :age persons))
153
(reduce + (map :age persons))
(reduce + '(42 44 29 38))
(+ (+ (+ 42 44) 29) 38)
(+ (+ 86 29) 38)
29 © 2009 Howard Lewis Ship

30. reduce
f
user=> (map :age persons)
(42 44 29 38)
user=> (reduce + (map :age persons))
153
(reduce + (map :age persons))
(reduce + '(42 44 29 38))
(+ (+ (+ 42 44) 29) 38)
(+ (+ 86 29) 38)
(+ 115 38)
30 © 2009 Howard Lewis Ship

31. reduce
f
user=> (map :age persons)
(42 44 29 38)
user=> (reduce + (map :age persons))
153
(reduce + (map :age persons))
(reduce + '(42 44 29 38))
(+ (+ (+ 42 44) 29) 38)
(+ (+ 86 29) 38)
(+ 115 38)
153
31 © 2009 Howard Lewis Ship

32. reduce
f
user=> (def input-string "Clojure is a fascinating language with unique
capabilities and total integration with Java.")
#'user/input-string
user=> (seq input-string)
(C l o j u r e space i s space a space f a s c i n a
t i n g space l a n g u a g e space w i t h space u
n i q u e space c a p a b i l i t i e s space a n d
space t o t a l space i n t e g r a t i o n space w
i t h space J a v a .)
user=> (reduce
(fn [m k] (update-in m [k] #(if (nil? %) 1 (inc %))))
Optional initial value {}
(seq input-string))
{space 12, a 12, b 1, C 1, c 2, d 1, e 5, f 1, g 4, h 2, i 11,
J 1, j 1, l 4, . 1, n 7, o 3, p 1, q 1, r 2, s 3, t 8, u 4,
v 1, w 2}
user=>
32 © 2009 Howard Lewis Ship

33. filter / remove
La
zy
f
?
user=> (remove #(< (% :age) 30) persons)
({:first-name "Howard", :last-name "Lewis Ship", :age 42}
{:first-name "Scott", :last-name "Simon", :age 44})
user=> (filter #(< (% :age) 30) persons)
({:first-name "Molly", :last-name "Newman", :age 29})
user=>
33 © 2009 Howard Lewis Ship

34. apply
f
user=> (map :age persons)
(42 44 29)
user=> (apply + (map :age persons))
115
user=>
(apply + (map :age persons))
(apply + '(42 44 29))
(+ 42 44 29)
115
34 © 2009 Howard Lewis Ship

35. Clojure Compilation
35 © 2009 Howard Lewis Ship

36. Function Calls
(remove nil? coll)
IFn
invoke() : Object
invoke(Object) : Object
Namespace invoke(Object, Object) : Object
…
applyTo(ISeq) : Object
Var
get() clojure.core$remove__4782 PersistentMap Keyword
36 © 2009 Howard Lewis Ship

37. Compiled to Bytecode
(defn first-non-nil
"Returns the first non-nil value from the collection."
[coll]
(first (remove nil? coll)))
package com.howardlewisship.cascade.internal;
import clojure.lang.*;
public class utils$first_non_nil__24 extends AFunction
{
public Object invoke(Object coll)
throws Exception
{
return ((IFn)const__0.get()).invoke(((IFn)const__1.get()).
invoke(const__2.get(), coll = null));
}
public static final Var const__0 = (Var)RT.var("clojure.core", "first");
public static final Var const__1 = (Var)RT.var("clojure.core", "remove");
public static final Var const__2 = (Var)RT.var("clojure.core", "nil?");
public utils$first_non_nil__24()
{
}
}
37 © 2009 Howard Lewis Ship

38. Compiled to Bytecode
(defn first-non-nil
"Returns the first non-nil value from the collection."
[coll]
(first (remove nil? coll)))
package com.howardlewisship.cascade.internal;
import clojure.lang.*;
public class utils$first_non_nil__24 extends AFunction
{
public Object invoke(Object coll)
throws Exception
{
return ((IFn)const__0.get()).invoke(((IFn)const__1.get()).
invoke(const__2.get(), coll = null));
}
public static final Var const__0 = (Var)RT.var("clojure.core", "first");
public static final Var const__1 = (Var)RT.var("clojure.core", "remove");
public static final Var const__2 = (Var)RT.var("clojure.core", "nil?");
public utils$first_non_nil__24()
{
}
}
38 © 2009 Howard Lewis Ship

39. Compiled to Bytecode
(defn first-non-nil
"Returns the first non-nil value from the collection."
[coll]
(first (remove nil? coll)))
package com.howardlewisship.cascade.internal;
import clojure.lang.*;
public class utils$first_non_nil__24 extends AFunction
{
public Object invoke(Object coll)
throws Exception
{
return ((IFn)const__0.get()).invoke(((IFn)const__1.get()).
invoke(const__2.get(), coll = null));
}
public static final Var const__0 = (Var)RT.var("clojure.core", "first");
public static final Var const__1 = (Var)RT.var("clojure.core", "remove");
public static final Var const__2 = (Var)RT.var("clojure.core", "nil?");
public utils$first_non_nil__24()
{
}
}
39 © 2009 Howard Lewis Ship

40. Compiled to Bytecode
(defn first-non-nil
"Returns the first non-nil value from the collection."
[coll]
(first (remove nil? coll)))
package com.howardlewisship.cascade.internal;
import clojure.lang.*;
public class utils$first_non_nil__24 extends AFunction
{
public Object invoke(Object coll)
throws Exception
{
return ((IFn)const__0.get()).invoke(((IFn)const__1.get()).
invoke(const__2.get(), coll = null));
}
public static final Var const__0 = (Var)RT.var("clojure.core", "first");
public static final Var const__1 = (Var)RT.var("clojure.core", "remove");
public static final Var const__2 = (Var)RT.var("clojure.core", "nil?");
public utils$first_non_nil__24()
{
}
}
40 © 2009 Howard Lewis Ship

41. Compiled to Bytecode
(defn format-date
[env params]
(let [#^Date date (params :date)
package app1; #^DateFormat fmt (DateFormat/getDateTimeInstance
DateFormat/MEDIUM
import clojure.lang.*; DateFormat/MEDIUM)]
import java.text.DateFormat; (.format fmt date)))
import java.util.Date;
public class fragments$format_date__21 extends AFunction
{
public Object invoke(Object env, Object params)
throws Exception
{
Object date = ((IFn)params).invoke(const__1);
Object fmt = DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.MEDIUM);
env = null;
params = null;
date = null;
fmt = null;
return ((DateFormat)fmt).format((Date)date);
}
public static final Var const__0 = (Var)RT.var("clojure.core", "let");
public static final Object const__1 = Keyword.intern(Symbol.create(null, "date"));
public fragments$format_date__21()
{
}
}
41 © 2009 Howard Lewis Ship

42. Compiled to Bytecode
(defn format-date
[env params]
(let [#^Date date (params :date)
package app1; #^DateFormat fmt (DateFormat/getDateTimeInstance
DateFormat/MEDIUM
import clojure.lang.*; DateFormat/MEDIUM)]
import java.text.DateFormat; (.format fmt date)))
import java.util.Date;
public class fragments$format_date__21 extends AFunction
{
public Object invoke(Object env, Object params)
throws Exception
{
Object date = ((IFn)params).invoke(const__1);
Object fmt = DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.MEDIUM);
env = null;
params = null;
date = null;
fmt = null;
return ((DateFormat)fmt).format((Date)date);
}
public static final Var const__0 = (Var)RT.var("clojure.core", "let");
public static final Object const__1 = Keyword.intern(Symbol.create(null, "date"));
public fragments$format_date__21()
{
}
}
42 © 2009 Howard Lewis Ship

43. Compiled to Bytecode
(defn format-date
[env params]
(let [#^Date date (params :date)
package app1; #^DateFormat fmt (DateFormat/getDateTimeInstance
DateFormat/MEDIUM
import clojure.lang.*; DateFormat/MEDIUM)]
import java.text.DateFormat; (.format fmt date)))
import java.util.Date;
public class fragments$format_date__21 extends AFunction
{
public Object invoke(Object env, Object params)
throws Exception
{
Object date = ((IFn)params).invoke(const__1);
Object fmt = DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.MEDIUM);
env = null;
params = null;
date = null;
fmt = null;
return ((DateFormat)fmt).format((Date)date);
}
public static final Var const__0 = (Var)RT.var("clojure.core", "let");
public static final Object const__1 = Keyword.intern(Symbol.create(null, "date"));
public fragments$format_date__21()
{
}
}
43 © 2009 Howard Lewis Ship

44. Compiled to Bytecode
(defn format-date
[env params]
(let [#^Date date (params :date)
package app1; #^DateFormat fmt (DateFormat/getDateTimeInstance
DateFormat/MEDIUM
import clojure.lang.*; DateFormat/MEDIUM)]
import java.text.DateFormat; (.format fmt date)))
import java.util.Date;
public class fragments$format_date__21 extends AFunction
{
public Object invoke(Object env, Object params)
throws Exception
{
Object date = ((IFn)params).invoke(const__1);
Object fmt = DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.MEDIUM);
env = null;
params = null;
date = null;
fmt = null;
return ((DateFormat)fmt).format((Date)date);
}
public static final Var const__0 = (Var)RT.var("clojure.core", "let");
public static final Object const__1 = Keyword.intern(Symbol.create(null, "date"));
public fragments$format_date__21()
{
}
}
44 © 2009 Howard Lewis Ship

45. Compiled to Bytecode
(defn format-date
[env params]
(let [#^Date date (params :date)
package app1; #^DateFormat fmt (DateFormat/getDateTimeInstance
DateFormat/MEDIUM
import clojure.lang.*; DateFormat/MEDIUM)]
import java.text.DateFormat; (.format fmt date)))
import java.util.Date;
public class fragments$format_date__21 extends AFunction
{
public Object invoke(Object env, Object params)
throws Exception
{
Object date = ((IFn)params).invoke(const__1);
Object fmt = DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.MEDIUM);
env = null;
params = null;
date = null;
fmt = null;
return ((DateFormat)fmt).format((Date)date);
}
public static final Var const__0 = (Var)RT.var("clojure.core", "let");
public static final Object const__1 = Keyword.intern(Symbol.create(null, "date"));
public fragments$format_date__21()
{
}
}
45 © 2009 Howard Lewis Ship

46. Ahead of Time Compilation
app/fragments.clj
(ns app.fragments
(:import (java.util Date)
(java.text DateFormat)))
(defn format-date
[env params]
(…))
Compiler
app/fragments__init.class
app/fragments$format_date__21.class
46 © 2009 Howard Lewis Ship

47. Ahead Of Time Compilation
build.xml
<target name="compile" description="Compile Clojure sources.">
<mkdir dir="${classes.dir}" />
<pathconvert pathsep=" " property="compile.namespaces">
<fileset dir="${src.dir}" includes="**/*.clj" />
<chainedmapper>
<packagemapper from="${basedir}/${src.dir}/*.clj" to="*" />
<filtermapper>
<replacestring from="_" to="-" />
</filtermapper>
</chainedmapper>
</pathconvert>
<java classname="clojure.lang.Compile">
<classpath>
<path refid="libs.path" />
<path location="${classes.dir}" />
<path location="${src.dir}" />
</classpath>
<sysproperty key="clojure.compile.path" value="${classes.dir}" />
<arg line="${compile.namespaces}" />
</java>
</target>
47 © 2009 Howard Lewis Ship

48. Ahead Of Time Compilation
build.xml
<target name="compile" description="Compile Clojure sources.">
<mkdir dir="${classes.dir}" />
<pathconvert pathsep=" " property="compile.namespaces">
<fileset dir="${src.dir}" includes="**/*.clj" />
<chainedmapper>
<packagemapper from="${basedir}/${src.dir}/*.clj" to="*" />
<filtermapper>
<replacestring from="_" to="-" />
</filtermapper> Locate *.clj under
</chainedmapper> ${src.dir} and convert to
</pathconvert>
namespace names
<java classname="clojure.lang.Compile">
<classpath>
<path refid="libs.path" />
<path location="${classes.dir}" />
<path location="${src.dir}" />
</classpath>
<sysproperty key="clojure.compile.path" value="${classes.dir}" />
<arg line="${compile.namespaces}" />
</java>
</target>
48 © 2009 Howard Lewis Ship

49. Ahead Of Time Compilation
build.xml
<target name="compile" description="Compile Clojure sources.">
<mkdir dir="${classes.dir}" />
<pathconvert pathsep=" " property="compile.namespaces">
<fileset dir="${src.dir}" includes="**/*.clj" />
<chainedmapper>
<packagemapper from="${basedir}/${src.dir}/*.clj" to="*" />
<filtermapper>
<replacestring from="_" to="-" />
</filtermapper>
</chainedmapper>
</pathconvert> clojure.jar, source
<java classname="clojure.lang.Compile">
directory and output
<classpath> directory must be on
<path refid="libs.path" /> classpath
<path location="${classes.dir}" />
<path location="${src.dir}" />
</classpath>
<sysproperty key="clojure.compile.path" value="${classes.dir}" />
<arg line="${compile.namespaces}" />
</java>
</target>
49 © 2009 Howard Lewis Ship

50. Ahead Of Time Compilation
build.xml
<target name="compile" description="Compile Clojure sources.">
<mkdir dir="${classes.dir}" />
<pathconvert pathsep=" " property="compile.namespaces">
<fileset dir="${src.dir}" includes="**/*.clj" />
<chainedmapper>
<packagemapper from="${basedir}/${src.dir}/*.clj" to="*" />
<filtermapper>
<replacestring from="_" to="-" />
</filtermapper>
</chainedmapper>
</pathconvert>
Output directory for
<java classname="clojure.lang.Compile"> generated classes
<classpath>
<path refid="libs.path" />
<path location="${classes.dir}" />
<path location="${src.dir}" />
</classpath>
<sysproperty key="clojure.compile.path" value="${classes.dir}" />
<arg line="${compile.namespaces}" />
</java>
</target>
List of namespaces to
compile
50 © 2009 Howard Lewis Ship

51. Clojure Pitfalls
51 © 2009 Howard Lewis Ship

52. IDE Support
52 © 2009 Howard Lewis Ship

53. Laziness
RuntimeException:
Divide by zero
53 © 2009 Howard Lewis Ship

54. Laziness
Clojure 1.0.0-
1:1 user=> (def nums (map / (range 0 10) (reverse (range 0 10))))
#'user/nums
1:2 user=> nums
java.lang.ArithmeticException: Divide by zero
(0 1/8 2/7 1/2 4/5 5/4 2 7/2 1:3 user=> (.. *e getCause printStackTrace)
java.lang.ArithmeticException: Divide by zero
at clojure.lang.Numbers.divide(Numbers.java:138)
at clojure.core$_SLASH___3350.invoke(core.clj:575)
at clojure.core$map__3815$fn__3822.invoke(core.clj:1508)
at clojure.lang.LazySeq.seq(LazySeq.java:41)
at clojure.lang.Cons.next(Cons.java:37)
at clojure.lang.RT.next(RT.java:560)
at clojure.core$next__3117.invoke(core.clj:50)
at clojure.core$nthnext__4405.invoke(core.clj:2531)
at clojure.core$print_sequential__5354.invoke(core_print.clj:53)
at clojure.core$fn__5439.invoke(core_print.clj:136)
at clojure.lang.MultiFn.invoke(MultiFn.java:161)
at clojure.core$pr_on__4145.invoke(core.clj:2020)
at clojure.core$pr__4148.invoke(core.clj:2030)
at clojure.lang.AFn.applyToHelper(AFn.java:173)
at clojure.lang.RestFn.applyTo(RestFn.java:137)
at clojure.core$apply__3243.doInvoke(core.clj:390)
at clojure.lang.RestFn.invoke(RestFn.java:428)
at clojure.core$prn__4159.doInvoke(core.clj:2053)
at clojure.lang.RestFn.invoke(RestFn.java:413)
at clojure.main$repl__5813$read_eval_print__5825.invoke(main.clj:177)
at clojure.main$repl__5813.doInvoke(main.clj:193)
at clojure.lang.RestFn.invoke(RestFn.java:876)
at clojure.contrib.repl_ln$repl__84.doInvoke(repl_ln.clj:259)
at clojure.lang.RestFn.invoke(RestFn.java:426)
at clojure.contrib.repl_ln$_main__44.doInvoke(repl_ln.clj:136)
at clojure.lang.RestFn.applyTo(RestFn.java:142)
at clojure.contrib.repl_ln.main(Unknown Source)
nil
1:7 user=>
54 © 2009 Howard Lewis Ship

55. Lack of Type Checking
55 © 2009 Howard Lewis Ship

56. Spot the Error
view_manager.clj
(defn to-dom-node-seq
[any]
"Converts the result of a render function to a seq as needed."
(cond
(nil? any) nil
(sequential? any) any
; A map is assumed to be a DOM node, wrap it in a vector
(map? any) [map]
(string? any) [(struct-map dom-node :type :text :value any)]
true (throw (RuntimeException. (format "A rendering function returned %s. ↵
Rendering functions should return nil, a string, a seq of DOM nodes, or a single ↵
DOM node."
(pr-str any))))))
56 © 2009 Howard Lewis Ship

57. Exception
ERROR in (simple-view-and-fragment) (test_is.clj:657)
Uncaught exception, not in assertion.
expected: nil
actual: java.lang.IllegalArgumentException: Wrong number of args passed to: core$map
at clojure.lang.AFn.throwArity (AFn.java:449)
clojure.lang.RestFn.invoke (RestFn.java:417)
com.howardlewisship.cascade.dom$fn__960.doInvoke (dom.clj:58)
clojure.lang.RestFn.invoke (RestFn.java:443)
clojure.lang.MultiFn.invoke (MultiFn.java:165)
com.howardlewisship.cascade.dom/render_xml_with_ns (dom.clj:118)
com.howardlewisship.cascade.dom/render_xml (dom.clj:125)
com.howardlewisship.cascade.test_views/render (test_views.clj:27)
com.howardlewisship.cascade.test_views/test_view (test_views.clj:56)
com.howardlewisship.cascade.test_views/test_view (test_views.clj:52)
com.howardlewisship.cascade.test_views/fn (test_views.clj:62)
dom.clj
(defmulti render-node-xml
(fn [node & rest]
(node :type)))
57 © 2009 Howard Lewis Ship

58. Spot the Error
view_manager.clj
(defn to-dom-node-seq
[any]
"Converts the result of a render function to a seq as needed."
(cond
(nil? any) nil
(sequential? any) any
; A map is assumed to be a DOM node, wrap it in a vector
(map? any) [map]
(string? any) [(struct-map dom-node :type :text :value any)]
true (throw (RuntimeException. (format "A rendering function returned %s. ↵
Rendering functions should return nil, a string, a seq of DOM nodes, or a single ↵
DOM node."
(pr-str any))))))
Returning function clojure.core/map;
should return any (the parameter)
58 © 2009 Howard Lewis Ship

59. Bus Factor
59 © 2009 Howard Lewis Ship

60. GitHub Factor
60 © 2009 Howard Lewis Ship

61. Performance
61 © 2009 Howard Lewis Ship

62. Performance
(defn shorts-to-bytes [#^shorts src #^bytes dst words]
(loop [src-offset (int 0)
dst-offset (int 0)]
(when (< src-offset words)
(let [sample (short (aget src src-offset))]
(aset-byte dst dst-offset (byte sample))
(aset-byte dst (inc dst-offset) (byte (bit-shift-right sample 8))))
(recur (inc src-offset) (unchecked-add 2 dst-offset)))))
public static void shortsToBytes(short[] src, byte[] dst, int len)
{
int idx = 0; 900 ms
short s;
while (len-- > 0) {
s = src[idx];
dst[idx*2] = (byte)s; 675 ms
dst[idx*2+1] = (byte)(s>>>8);
idx++;
}
}
450 ms
225 ms
0 ms
Java Clojure
62 © 2009 Howard Lewis Ship

63. API Docs
63 © 2009 Howard Lewis Ship

64. Wrap Up
64 © 2009 Howard Lewis Ship

65. What's Not Covered?
• multimethods ➠ inheritance-like function
dispatch
• Concurrency Support ➠ atoms, agents, refs
& vars
http://www.clojure.org
• loop & recur ➠ iterative-style coding
• clojure.contrib ➠ Community library
• Macros & Meta-Programming ➠ Create the language you want inside
Clojure
• Tuning Clojure Performance
• More ….
65 © 2009 Howard Lewis Ship

66. Stuart Halloway
Pragmatic Bookshelf
http://pragprog.com/titles/shcloj/programming-clojure
66 © 2009 Howard Lewis Ship

67. http://jnb.ociweb.com/jnb/jnbMar2009.html
67 © 2009 Howard Lewis Ship

68. Image Credits
© 2005 Jean-Philippe Daigle
http://www.flickr.com/photos/jpdaigle/59942231/
© 2007 Howard Gees
http://www.flickr.com/photos/cyberslayer/952121271/
© 2006 Simon Law
http://www.flickr.com/photos/sfllaw/222795669/
© 2008 II-cocoy22-II
http://www.flickr.com/photos/30954876@N07/3090155264/
© 2009 Martin Biskoping
http://www.flickr.com/photos/mbiskoping/3388639698/
© 2008 sea turtle
http://www.flickr.com/photos/sea-turtle/3049443478/
© 2009 Tulio Bertorini
http://www.flickr.com/photos/tuliobertorini/3159130251/
© 2007 Adam Balch
http://www.flickr.com/photos/triplemaximus/795758146/
© 2008 jessamyn west
http://www.flickr.com/photos/iamthebestartist/2636607001/
68 © 2009 Howard Lewis Ship