Rigor Mortis - YOW! Conferences...Ludwig Wittgenstein 13 How far my efforts agree with those of...

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Dav

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omas

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dave

(avoiding)Rigor Mortis

Dave is anOldFart

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Old FartsGet Stuck in Their Ways

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So Do Young Ones

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We Get

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Maintenance

Programmer

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The future is functional

The future is concurrent

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Is teaching me a new vocabularyIs changing the way I think

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Token Appeal to Authority

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Ludwig Wittgenstein

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Ludwig Wittgenstein

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How far my efforts agree with those of other philosophers I will not decide. Indeed what I have here written makes no claim to novelty

in points of detail; and therefore I give no sources, because it is indifferent to me

whether what I have thought has already been thought before me by another.

Logico-Tractatus Philosophicus

Ludwig Wittgenstein Logico-Tractatus Philosophicus

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How far my efforts agree with those of other philosophers I will not decide. Indeed what I have here written makes no claim to novelty

in points of detail; and therefore I give no sources, because it is indifferent to me

whether what I have thought has already been thought before me by another.

The limits of my language are the

limits of my worldLudwig Wittgenstein—Logico-Tractatus Philosophicus

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How Has Learning Elixir Changed the Way I Think?

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Functional |> Concurrent |> Pragmatic |> Fun

Functional |> Concurrent |> Pragmatic |> Fun

Different

Background

• Pattern matching

• Functions transform data

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Pattern Matcha = 1

{ c, d } = { 2, 3 }

[ e, f, g ] = [ 4, 5, 6 ]

"Elixir " <> rest = "Elixir Rocks!" # rest => "Rocks!"

[ head | tail ] = [ 1, 2, 3, 4, 5, 6 ] # head => 1 # tail => [ 2,3,4,5,6 ]

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Pattern Match

case File.open("myfile") do

{ :ok, device } -> IO.read(device, :line)

{ :error, reason } -> IO.puts "FAILED #{reason}"

end

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Pattern Matchmy_fun = fn :plus, a, b -> a + b :times, a, b -> a * b end

IO.puts my_fun.(:plus, 3, 4) # => 7 IO.puts my_fun.(:times, 3, 4) # => 12

def other_fun(:minus, a, b), do: a - b def other_fun(:divide, a, b), do: a/b

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Pattern Matching• Match based on shape and content

• Destructure data

• Recursive

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For example…• fib(0) → 0

• fib(1) → 1

• fib(n) → fib(n-1) + fib(n-2)

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Fibonaccidefmodule Fib do

def fib(0), do: 0 def fib(1), do: 1 def fib(n), do: fib(n-1) + fib(n-2)

end

IO.puts Fib.fib(10)

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• fib(0) → 0

• fib(1) → 1

• fib(n) → fib(n-1) + fib(n-2)

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defmodule Fib do def fib(0), do: 0 def fib(1), do: 1 def fib(n), do: fib(n-1) + fib(n-2) end

Programs Reflect Specification

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Programs Reflect Specification

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Implementation Reflects Transformation

Length of List

• Length of empty list is zero

• Length of list with head “h” and tail “t” is 1 + length(t)

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• Length of empty list is zero

• Length of list with head “h” and tail “t” is 1 + length(t)

defmodule MyList do

def len([]), do: 0

def len([ _head | tail ]), do: 1 + len(tail)

end

IO.puts MyList.len [ 5, 4, 3 ]

Map

• Map of an empty list is an empty list

• Map of list with head “h” and tail “t” is a list whose head is func(h) and whose tail is map(t)

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defmodule MyList do

def map([], _func), do: []

def map([ h | t ], func), do: [ func.(h) | map(t, func) ]

end

MyList.map [ 1,2,3,4,5], &(&1*&1)

• Map of an empty list is an empty list

• Map of list with head “h” and tail “t” is a list whose head is func(h) and whose tail is map(t)

More Practical

• Run-length encode a list of values:Runs of two or more of the same value “v” are replaced with { v, count }

[ 1, 2, 2, 2, 3, 4, 4, 5, 6, 6, 6, 6 ]

→ [ 1, {2, 3}, 3, {4, 2}, 5, {6, 4} ]

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[ 1, 2, 2, 2, 3, 4, 4, 5, 6, 6, 6, 6 ]

→ [ ]

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[ 2, 2, 2, 3, 4, 4, 5, 6, 6, 6, 6 ]

→ [ 1 ]

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[ {2,2}, 2, 3, 4, 4, 5, 6, 6, 6, 6 ]

→ [ 1 ]

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[ {2,3}, 3, 4, 4, 5, 6, 6, 6, 6 ]

→ [ 1 ]

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[ 3, 4, 4, 5, 6, 6, 6, 6 ]

→ [ {2, 3}, 1 ]

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[ 4, 4, 5, 6, 6, 6, 6 ]

→ [ 3, {2, 3}, 1 ]

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[ {4,2}, 5, 6, 6, 6, 6 ]

→ [ 3, {2, 3}, 1 ]

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[ 5, 6, 6, 6, 6 ]

→ [ {4,2} , 3, {2,3}, 1 ]

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RLEdefmodule Rle do def encode(list), do: _encode(list, [])

end

RLE.encode [ 1, 2, 2, 2, 3, 4, 4, 5, 6, 6, 6, 6 ]

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end

RLE.encode [ 1, 2, 2, 2, 3, 4, 4, 5, 6, 6, 6, 6 ]

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def _encode( [ a | tail ], result) do _encode(tail, [ a | result ]) end


end

RLE.encode [ 1, 2, 2, 2, 3, 4, 4, 5, 6, 6, 6, 6 ]

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def _encode( [ {a, n}, a | tail ], result) do _encode( [ {a, n+1} | tail ], result ) end


end

RLE.encode [ 1, 2, 2, 2, 3, 4, 4, 5, 6, 6, 6, 6 ]

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def _encode([ a, a | tail ], result) do _encode( [ {a, 2} | tail ], result ) end


end

RLE.encode [ 1, 2, 2, 2, 3, 4, 4, 5, 6, 6, 6, 6 ]

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def _encode([], result), do: Enum.reverse(result)





end

RLE.encode [ 1, 2, 2, 2, 3, 4, 4, 5, 6, 6, 6, 6 ]

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def _encode([], result), do: Enum.reverse(result)




Input New input Result

[] «done» → [ values ]

[a,a,…] [ {a,2}, … ] → [ values ]

[{a,n}, a, … ] [ {a,n+1}, … ] → [ values ]

[b, …] [ … ] → [ b, values ]

RLE

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State New State Result

[] «done» → [ values ]

[a,a,…] [ {a,2}, … ] → [ values ]

[{a,n}, a, … ] [ {a,n+1}, … ] → [ values ]

[b, …] [ … ] → [ b, values ]

RLE

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RLEdefmodule Rle do

def encode(list) do list |> Enum.reduce([], &_encode/2) |> Enum.reverse end

def _encode(next, result) do case {next, result} do {a, [ a | rest ] } -> [ {a,2} | rest ] {a, [ {a,n} | rest ] } -> [ {a, n+1} | rest ] {a, rest } -> [ a | rest ] end end end

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Not New

• Decision tables (1960s)

• State Machines (1960s)

• Blackboard systems (1980s)

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1960s

RLEdefmodule Rle do



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Transformation

RLEdefmodule Rle do



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Event + State

RLEdefmodule Rle do



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TransitionsEvent + State

Markdown

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System Types ============

These types reflect resources in the underlying Erlang VM.

IDs and Ports -------------

A PID is a reference to a local or remote process, and a port is a reference to a resource (typically external to the application) that you'll be reading or writing.

Markdown defp parse([ %Line.Blank{}, %Line.Text{content: heading}, %Line.SetextUnderlineHeading{level: level}

| rest ], result) do

parse(rest, [ %Heading{content: heading, level: level} | result ]) end

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Large Scale, Too

• REST Service Request: get_special_offers_for_user

• identify user from auth token• find local offers• find national offers• merge and respond

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} asynchronous

Find local offers Find national offers

Lookup User

Format response

Request: auth token

Response: . . .

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%{ get_offers: auth } -> %{ get_offers: auth, user: user_from(auth) }

%{ get_offers: auth, user: nil } -> %{ respond: :not_authorized }

%{ get_offers: auth, user: user } -> async_get_local_offers(user) async_get_national_offers(user)

%{ get_offers: auth, user_user, national: :error }, -> respond_with_error

%{ get_offers: auth, user_user, local: :error }, -> respond_with_error

%{ get_offers: auth, user_user, national: national, local: local }, -> format_response(user, national, local)

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Enough Already

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The Point

• Pattern matches are the rules in a state machine

• Each match specifies a transformation of state

• The transformation is the application of functions

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Interesting Opportunities

• Easily made parallel

• DSL could define business flow

• granular reuse

• easier testing

• better error handling

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Think Differently

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Program Differently

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Program Differently• New languages are an opportunity

• Let’s not recreate where we came from

• Let’s have fun

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My name is Inigo Montoya. You killed my programming paradigm. Prepare to learn.

Dave ThomasPragmatic Programmers@/+pragdave

Rigor Mortis - YOW! Conferences...Ludwig Wittgenstein 13 How far my efforts agree with those of...

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