Metaprogramming Ruby - What the hell's a DSL? murphee (Werner - - PowerPoint PPT Presentation

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Metaprogramming Ruby - What the hell's a DSL? murphee (Werner - - PowerPoint PPT Presentation

Dec 27, 2022 164 likes •756 views

Metaprogramming Ruby - What the hell's a DSL? murphee (Werner Schuster) Blog @ http://jroller.com/page/murphee Meta? Programs that write Programs Compiler DSLs Regexes, anyone? Always good to start with quotes by... Alan Kay The

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Metaprogramming Ruby - What the hell's a DSL?

  • murphee (Werner Schuster)
  • Blog @ http://jroller.com/page/murphee
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Meta?

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Programs that write Programs

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Compiler

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DSLs

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Regexes, anyone?

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Always good to start with quotes by...

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Alan Kay

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The general attitude seems to be that people should wear square shoes, because squares are easier to design and manufacture than foot shaped shoes. ...

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If the shoe industry has gone the way of the computer industry it would now be running a $200-a- day course on how to walk, run and jump in square shoes."

Alan Kay

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DSLs

  • Internal

– use host language

  • External

– Yacc, ANTLR, ...

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Executable Spec

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Let's start with... Dylan

  • http://www.networknightvision.com/
  • Dylan
  • declarative protocol spec
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Ethernet spec in Dylan

define protocol ethernet−frame ( header−frame ) summary ”ETH %= −> %=/%s ” , source−address , destination−address , compose ( summary , payload ) ; field destination−address : : <mac−address >; field source−address : : <mac−address >; field type−code : : <2byte−big−endian−unsigned−integer >; var iably−typed−field payload , type−function: select ( frame . type−code ) #x800 => <ipv4−frame >; #x806 => <arp−frame >;

  • therwise => <raw−frame >;

end ; end ;

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Ethernet spec in Dylan

define protocol ethernet−frame ( header−frame )

summary ”ETH %= −> %=/%s ” , source−address , destination−address , compose ( summary , payload ) ; field destination−address : : <mac−address >; field source−address : : <mac−address >; field type−code : : <2byte−big−endian−unsigned−integer >; var iably−typed−field payload , type−function: select ( frame . type−code ) #x800 => <ipv4−frame >; #x806 => <arp−frame >;

  • therwise => <raw−frame >;

end ; end ;

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Ethernet spec in Dylan

define protocol ethernet−frame ( header−frame ) summary ”ETH %= −> %=/%s ” , source−address , destination−address , compose ( summary , payload ) ; field destination−address : : <mac−address >; field source−address : : <mac−address >; field type−code : : <2byte−big−endian−unsigned−integer >; var iably−typed−field payload , type−function:

select ( frame . type−code )

#x800 => <ipv4−frame >; #x806 => <arp−frame >;

  • therwise => <raw−frame >;

end ; end ;

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Design Process

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Incremental does it

  • Sketching
  • Make it work
  • ?
  • Profit!
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Example time

  • http://www.infoq.com/articles/properties-metaprogramming
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Properties in Ruby/1

  • C#-like Properties in Ruby
  • Why?

– to piss of Java zealots

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Properties in Ruby/2 - Sketching

class Foo property name end

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Properties in Ruby/2 - Sketching

class Foo property name end NameError: undefined local variable or method `name' for main:Object

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Properties in Ruby/3 - Fix

class Foo property :name end

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Properties in Ruby/3 - Fix

class Foo property :name end NameError: undefined method `property' for main:Object

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Properties in Ruby/3 - Fix

def property(sym) ... end

class Foo property :name end

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Properties in Ruby/3 - Fix

def property(sym) define_method("#{sym}=") do |value|

instance_variable_set("@#{sym}", value) end

end class Foo property :name end

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Properties in Ruby/3 - Fix

def property(sym) define_method("#{sym}=") do |value|

instance_variable_set("@#{sym}", value) end

end class Foo property :name end name=

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Properties in Ruby/3 - Fix

def property(sym) define_method("#{sym}=") do |value|

instance_variable_set("@#{sym}", value) end

end class Foo property :name end @name

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Properties in Ruby/4 - Expand

def property(*sym, &bl) # Code: Homework define_method("#{sym}=") do |value| # More Homework instance_variable_set("@#{sym}", value) end end class Tower property(:width, :height) {|val| val > 200} end

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What we know by now

  • Class definitions are executed
  • Symbols are nice
  • Blocks too
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Another one

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Pattern Matching

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Parseweasel

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Ruby ParseTree

foo.hello(1)

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Ruby ParseTree

foo.hello(1)

  • >

[:vcall, :hello, :foo, [:args, [:lit, 1] ] ]

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Ruby ParseTree

foo.hello(1)

  • >

[:vcall, :hello, :foo, [:args, [:lit, 1] ] ]

AST as: s-expr symbolic expression

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ParseWeasel pattern

[:vcall, :name_, :recv_, :args_]

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ParseWeasel pattern

[:vcall, :name_,:recv_, :args_] someone.something foo.bar murphee.speak

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ParseWeasel pattern/2

[:vcall, :hello,:recv_, :args_]

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ParseWeasel pattern/2

[:vcall, :hello,:recv_, :args_] foo.bar foo.hello huey().lewey().hello() huey().speak

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ParseWeasel handlers

handler([:vcall, :hello,:recv_, :args_]){|s| puts “Found a hello #{s[:recv]}” }

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ParseWeasel use case: optimizer

replace([:call, :op_, :*, [:lit, 0] ]){|s| [:lit, 0] }

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ParseWeasel use case: optimizer

replace([:call, :op_, :*, [:lit, 0] ]){|s| [:lit, 0] } x = foo * 0

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Ruby DSLs

  • Keep it simple
  • Stick to basics
  • If it limps like a hack

– it probably is one

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Let's push it further

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Let's mess up the syntax

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Hello LISP

(defun factorial (x) (if (zerop x) 1 (* x (factorial (- x 1))) ) ) (factorial 42)

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Macros

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C Preprocessor

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C Preprocessor

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LISP Macro example: Infix

(* a 42)

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I want my infix!

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LISP Macro example: Infix

(infix (a * 42) )

what I write

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LISP Macro example: Infix

(defmacro infix (one op two &rest body) `(,op ,one ,two ) ) (infix (a * 42) )

what I write

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LISP Macro example: Infix

(defmacro infix (one op two &rest body) `(,op ,one ,two ) ) (infix (a * 42) ) (* a 42)

what I write what gets executed

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LISP Macro: real use cases

  • Practical Lisp

– MP3 binary parser – executable spec

  • Many LISP control structures
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Macros in the real world

  • Mathematica

– D[x ^ 2] – Integrate[x ^ 3] – Expand[ x ^ 42] –

  • Macro-like
  • “FullForm” ~ s-expr

– 3x -> Times[3, x ]

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Let's wrap up

  • Practical Lisp

– http://www.gigamonkeys.com/book/

  • http://ola-bini.blogspot.com/2006/09/ruby-metaprogramming-techniques.html
  • http://www.infoq.com/articles/properties-metaprogramming