[PDF] - Rigor Mortis (avoiding) 1 Dave is an Old Fart PDF Document

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Dave Thomas  @/+pragdave

(avoiding)

Rigor Mortis

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Dave is an Old Fart

http://24.media.tumblr.com/tumblr_lr7ypweBfM1qa9b8ro1_500.png

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Old Farts Get Stuck in Their Ways

http://www.runningheads.net/wp-content/uploads/2013/05/Curmudgeon_Logo.jpg

SLIDE 4 http://www.clipartbest.com/clipart-MTLL5pbac

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So Do Young Ones

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We Get

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http://www.clker.com/cliparts/W/n/3/A/j/2/comfortable-man.svg

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We Get

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http://www.clker.com/cliparts/W/n/3/A/j/2/comfortable-man.svg

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http://www.clker.com/cliparts/W/n/3/A/j/2/comfortable-man.svg

Maintenance

Programmer

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I Got

http://www.clker.com/cliparts/W/n/3/A/j/2/comfortable-man.svg

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The future is functional The future is concurrent

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Is teaching me a new vocabulary Is changing the way I think

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T

ken 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

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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.

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The limits of my   language are the   limits of my world

Ludwig Wittgenstein—Logico-Tractatus Philosophicus 15

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How Has Learning Elixir Changed the Way I Think?

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Functional |> Concurrent |> Pragmatic |> Fun

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Functional |> Concurrent |> Pragmatic |> Fun

Different

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Background

Pattern matching
Functions transform data

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Pattern Match

a = 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 Match

my_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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Fibonacci

defmodule 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

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Programs Reflect Specification

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Programs Reflect Specification

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Implementation Reflects Transformation

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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 ]

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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)

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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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