Pattern Matching in Ruby Yuki Torii, Sep.20.2017

Who am I? ❖ a Rails Developer of Everyleaf Corporation. ❖ a Japanese translator of ❖ “Hello Ruby” series
 (By Linda Liucusʣ ❖ “Programing Elixir” 
 (By Dave Thomasʣ corporating with Koich Sasada ❖ a member of Rails Girls in JP

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The Goal of This Presentation ❖ Main: You want to use Pattern Matching in Ruby ❖ Sub: You know how to extend Ruby by Ruby

Agenda ❖ Demo 1 ❖ What is Pattern Matching ❖ The Detail of My Proposal ❖ Demo 2 (details) ❖ Implementation by (almost) Ruby 
 as a Conceptual Model ❖ Future Issues

First Demo(in live) Code Result

What is Pattern Matching “pattern matching is the act of checking a given sequence of tokens for the presence of the constituents of some pattern.” – WikiPedia Pattern matching
 https://en.wikipedia.org/wiki/Pattern_matching

What is Pattern Matching ❖ ex. Ruby’s Regexp is also Pattern Matching 1BUUFSO 4FRVFODFPG
 5PLFOT

What is Pattern Matching ❖ ex2. Elixir’s Pattern Matching ❖ Elixir is a functional programing language working on Erlang VM. ❖ Elixir’s grammar is influenced by Ruby ❖ It has powerful pattern matching system

What is Pattern Matching ❖ In Elixir, `=` is always Pattern Matching, 
 not assigning value

What is Pattern Matching ❖ More examples of Elixir

What is Pattern Matching ❖ Elixir has guards: more complex check. result#=> < guard clause

What is Pattern Matching ❖ Ruby’s Existing Pattern Matching gem “pattern- match”
 https://github.com/k-tsj/pattern-match

The detail of my proposal ❖ %p ❖ like %w, %i ❖ `=~` for matching Basic Usage

The detail of my proposal ❖ `===` is a alias of `=~`

Demo of details

demo(with case when statement) Code Result

demo(with hash, and _(ignored pattern)) Code Result

demo(nested pattern) Code Result

demo(with regexp) Code Result

demo(with Class of object) Code Result

Implementation as a concept model ❖ I wrote almost part of pm by Ruby.
 C-lang diff is only below: ❖ (show parse.y & complile.c diff ) ❖ What trick did I use? compile.c parse.y

Implementation as a concept model Ruby script Parse Compile Ruby byte code Evaluator

Implementation of the concept model Ruby script Parse Compile Ruby byte code PatternMatching %p([a, 1]) =~ [3, 1] “[a, 1]” variables list [“a”] Define variabies Evaluator pattern_match obj Parse pattern Convert script,
 Generate inspections with the additional code

How I implement it as concept model Ruby script Parse Compile Ruby byte code PatternMatching %p([a, 1]) =~ [3, 1] “[a, 1]” variables list Define variabies Evaluator pattern_match obj Parse pattern build AST check matching assign values variables list [“a”] Convert script,
 Generate inspections with the additional code Convert Script ?

Implementation of the concept model %p([a, 1]) =~ [3, 1] in Compiling to byte code Convert Script PatternMatch.save_binding(b)
 %p([a, 1]) =~ [3, 1] Ruby byte code save binding build AST check matching assign values build AST check matching assign values

Implementation of the concept model ❖ Ruby library ❖ Parse patterns ❖ Matching values ❖ Comparing ❖ Assignment

Back to the goals ❖ Main: you want to use Pattern Matching in Ruby ❖ Did it attract you? ❖ Sub: you know How to extend Ruby by Ruby ❖ Now you know the backdoor.

Special Thanks ❖ Koichi Sasada ❖ My great adviser of Ruby’s implementation. ❖ Tsujimoto-san ❖ the author of pattern-match gem.

Future Issues ❖ Syntax. Is %p the best for making pattern? ❖ Specification of Guard clause ❖ Improve the parser. ❖ https://github.com/yakitorii/pattern-match-ruby