Appengine ja-night-10

Mirah &
Dubious
Tuesday, August 31, 2010

Mirah & Dubious
A bold and beautiful way to write Java,
plus a new framework for App Engine
Charles Nutter
John Woodell
Aug 30, 2010

2


Mirah
A pragmatic blend of Ruby and Java


Me
• Charles Oliver Nutter
• Engine Yard, Inc
• headius@headius.com
• @headius
• JRuby core developer
• Mirah creator

Ruby
• Beautiful language
• Clean syntax
• Easy-to-use closures
• Nice core libraries
• “Slow” language
• Very dynamic == hard to optimize

Java
• High-performance language
• Mostly static typing
• Full system optimizations
• Primitive math operations
• Ugly language
• (C++)-- of 1995

Mirah
• “Apparent features” of Ruby
• Syntax
• Closures and iterators
• Dynamic-feeling behaviors
• Performance, typing like Java
• As fast as Java for almost everything

What If This...
public class Foo {
private int a;

public Foo(int a) {
this.a = a;
}

public void show() {
System.out.println(a);
}
}


...Could Be This
class Foo
def initialize(a)
@a = a
end

def show
puts @a
end
end


Mirah
class Foo
def initialize(a:int)
@a = a
end

def show
puts @a
end
end


“Java’s Ruby”

• A nicer way to write Java
• Ruby syntax with modiﬁcations
• Feels like Ruby
• Compiles to Java/JVM
• No runtime library


Features From Ruby
• Optional arguments ✓
• Internal iteration ✓
• Closures ✓
• Literals ✓
• String interpolation ✓
• Mixins, “open” classes (soon)

Features From X

• (Coming Soon)
• Extension methods (C#ish, but nicer)
• Implicit type conversions (Scala)
• Pattern matching?
• Case classes?


Ruby

puts “Hello, world!”


Mirah

puts “Hello, world!”


Mirah

// Generated from DashE
public class DashE extends java.lang.Object {
public static void main(java.lang.String[] argv) {
java.io.PrintStream temp$1 = java.lang.System.out;
temp$1.println("Hello, world!");
}
}


Ruby
def fib(a)
if a < 2
a
else
fib(a - 1) + fib(a - 2)
end
end


Mirah
def fib(a:int)
if a < 2
a
else
fib(a - 1) + fib(a - 2)
end
end


Mirah
}
public static int fib(int a) {
return (a < 2) ? (a) : ((DashE.fib((a - 1)) +
DashE.fib((a - 2))));
}
}


Ruby

def foo(a = 1, b = 2)
puts a + b
end


Mirah

def foo(a:int = 1, b:int = 2)
puts a + b
end


Mirah
public static java.io.PrintStream foo(int a, int b) {
java.io.PrintStream temp$1 =
java.lang.System.out;
temp$1.println((a + b));
return temp$1;
}
public static java.io.PrintStream foo() {
return foo(1);
}
public static java.io.PrintStream foo(int a) {
return foo(a, 2);
}


Ruby

a = [5,4,3,2,1]
a.each do |x|
puts x
end


Mirah

a = [5,4,3,2,1]
a.each do |x|
puts x
end


Mirah
java.util.List a =
java.util.Collections.unmodifiableList(
java.util.Arrays.asList(1, 2, 3, 4, 5));
java.util.Iterator __xform_tmp_1 = a.iterator();
label1:
while (__xform_tmp_1.hasNext()) {
java.lang.Object x = __xform_tmp_1.next();
label2:
{
temp$3.println(x);
}
}
}
}


Ruby

t = Thread.new do
puts “in thread”
end


Mirah

t = Thread.new do
puts “in thread”
end


Mirah
DashE.__xform_tmp_1 $binding = new DashE.__xform_tmp_1();
$binding.x = "in thread";
java.lang.Thread t = new java.lang.Thread(new DashE.__xform_tmp_2($binding));
}
public static class __xform_tmp_1 extends java.lang.Object {
java.lang.String x;
}
public static class __xform_tmp_2 extends java.lang.Object implements
java.lang.Runnable {
private DashE.__xform_tmp_1 binding;
public __xform_tmp_2(DashE.__xform_tmp_1 binding) {
this.binding = binding;
}
public void run() {
DashE.__xform_tmp_1 $binding = this.binding;
temp$1.println($binding.x);
}
}
}


Open Class (proposal)
interface StringFunc
def apply(str:String)
end

extend class String # java.lang.String
def each(func:StringFunc)
# String#split call from Java
lines = split

# like “for (String str: strArray)”
lines.each do |str|
func.apply(str)
end
end
end


Open Class (Java side)
public interface StringFunc {
public void apply(String str);
}

public class StringExtension {
public void each(String str, StringFunc func) {
for (String s: str.split()) {
func.apply(str);
}
}
}


Open Class (usage)

str = “hellongoodbyenworld”

str.each {|s| ... }


Open Class (Java usage)

String str = “hellongoodbyenworld”;

StringExtension.each(str, new StringFunc() {
public void apply(String s) {
...
}
});


Open Class (Java usage)

String str = “hellongoodbyenworld”;

StringExtension.each(str, new StringFunc() {
public void apply(String s) {
...

YUCK!
}
});


Type Conversion


# no “map” method on String...
str.map {|s| # ERROR


Type Conversion
(by hand)


# without type conversion
Arrays.asList(str.split).map { ...


Type Conversion
(proposal)
conversion(String => List) do |str|
Arrays.asList(str.split)
end

conversion(List => String) do |list|
list.join(‘n’)
end


Type Conversion
(usage)


# with type conversion!
str.map { ... # OK!!


It’s Not Ruby

• Using Java’s libraries and type system
• No “eval”
• No runtime-mutable classes
• Ruby libraries will not work


But It Feels Like Ruby!

• Clean, lightweight syntax
• Iteration, closures
• Far less “ceremony” than Java
• Performance equivalent to Java


mirah.org


Dubious
Dubious Mirah Web


Me

• John Woodell
• Web developer at Google
• Dubious creator
• App Engine JRuby maintainer
• @JohnWoodell


Thank you for using
"AppEngine/Java”
"AppEngine/Java"

47


Spin-up time can make scaling “painful”
• The most critical issue to be resolved is spin-up time,
App Engine scales by adding new application instances.
• Even if initialization could happen without affecting users
some apps will need to scale instantly.

48


Spin-up?
Yes, this is a problem...

49


...but now you can use
Mirah and Dubious

"Mirah/Dubious"

50


Dubious is Web framework for Mirah
Dubious Mirah Web

*du bi ous[ djbis | dj- ] [ ]
[1] (( )) …
((of, about, as to ...)).
[2]

>
51


Write Rails-style code,
it runs on Google App Engine

GoogleAppEngine
Rails

52


Benefits of Mirah on App Engine
• Ruby syntax & apparent features + Java type system
• Use Java or Ruby when Mirah lacks features you require
• The generated Java source can be inspected at any time
• Macros and plugins can be written in Ruby or Mirah
• New instances always spin-up in about a second

53


Working with Dubious
• Dubious framework uses familiar Rails conventions
• Generate JSONs or work with ERb templates
• MirahModel syntax is similar to DataMapper
• Developers can create apps entirely in Rails,
then refactor URLs that need to scale quickly
• Some important features are currently missing,
but “you” could have fun contributing them

54


Here’s code from Dubious
(this is not Rails)

Rails
Dubious

55


Dubious controllers will be familiar


Mirah can use ERb templates


The generated Java source can be inspected


The ERb is transformed into method calls


Your model definition is very concise


Code generation based on defined properties


All the basic methods you need are generated


It really works,
and spins-up in ~1sec

Spinup.

63


It isn’t "Dubious"

http://dubious-demo.appspot.com

64


The Framework
(coding in Mirah)


Method signatures enforce types


Return type can be enforced also


Code is very concise


Thank You


Appengine ja-night-10

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