Papers we love: Elixir edition

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PAPERS WE LOVE ELIXIR EDITION PAPERS WE LOVE ELIXIR EDITION

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@whatyouhide

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“You know Yelp? Yeah, but for weed”– me

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“You know Uber Eats?”– me

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weedmaps.com/careers

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ELIXIR functional concurrent fault tolerant

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The Elixir core team

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we existing research

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Formatting code Diffing data structures Property-based testing ⚙

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FORMATTING CODE

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Code formatter welcoming to newcomers consistency across teams/orgs/community no style discussions

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print code with line length limit

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%{foo: [1, 2, 3], bar: "baz"}

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%{foo: [1, 2, 3], bar: "baz"} 30

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%{foo: [1, 2, 3], bar: "baz"} 25

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%{ foo: [1, 2, 3], bar: "baz" } 25

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%{ foo: [1, 2, 3], bar: "baz" } 13

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%{ foo: [ 1, 2, 3 ], bar: "baz" } 13

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The Design of a Pretty-printing Library John Hughes

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Documents "text" concat(document1, document2) nest(document, columns)

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"[" |> concat("1,") |> concat("2,") |> concat("3") |> concat("]") [1, 2, 3]

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A Prettier Printer Philip Wadler

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choose( doc, replace_concat_with_line_break(doc) ) DANGER: STRICT LANGUAGE AHEAD

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Strictly Pretty Christian Lindig

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Our documents color(doc, :blue) nest(doc, :cursor) ...

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DIFFING DATA STRUCTURES

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1) test two strings are different (Test) test.ex:6 Assertion with == failed code: assert "hello world!" == "Hello, my world" left: "hello world!" right: "Hello, my world" stacktrace: test.ex:7: (test)

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An O(ND) Difference Algorithm and Its Variations Eugene W. Myers

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“Find the shortest edit script to turn a sequence A into a sequence B.” = Find shortest path in a graph

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O(ND) D is related to how "similar" the two sequences are DNA strand mutation source code changes

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iex> List.myers_difference([1, 4, 2, 3], [1, 2, 3, 4]) [eq: [1], del: [4], eq: [2, 3], ins: [4]]

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Now colorize

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No modifications to the paper this time

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String Matching with Metric Trees Using an Approximate Distance Ilaria Bartolini, Paolo Ciaccia, Marco Patella

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PROPERTY-BASED TESTING

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Shape of input Properties of output + + Randomness = Property-based testing

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check all list <- list_of(term()) do sorted = sort(list) assert is_list(sorted) assert length(list) == length(sorted) end

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String.starts_with?(s1 <> s2, s1) String.ends_with?(s1 <> s2, s2) For any strings s1 and s2:

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Only Erlang tools (with different license)

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QuickCheck: A Lightweight Tool for Random Testing of Haskell Programs Koen Classen John Hughes

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all the base ideas are there but it relies too heavily on types

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data Colour = Red | Blue | Green instance Arbitrary Colour where arbitrary = oneof [return Red, return Blue, return Green]

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(prop/for-all [v (gen/vector gen/int)] (= (sort v) (sort (sort v)))) Clojure's test.check

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StreamData check all s1 <- string(), s2 <- string() do assert String.starts_with?(s1 <> s2, s1) assert String.ends_with?(s1 <> s2, s2) end

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Generators functions that take some random state and return a lazy tree

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Lazy tree a value plus a "recipe" for shrinking it

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StreamData.integer() 3 0 2 0 1 0

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StreamData.integer() 3 0 2 0 1 0

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map(StreamData.integer(), fn x -> x * 2 end) 3 * 2 0 * 2 2 * 2 0 * 2 1 * 2 0 * 2

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map(StreamData.integer(), fn x -> x * 2 end) 6 0 4 0 2 0

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HONORABLE MENTIONS

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How to make ad-hoc polymorphism less ad hoc Philip Wadler Stephen Blott

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Recursive functions of symbolic expressions and their computation by machine John McCarthy

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Advances in record linkage methodology as applied to the 1985 census of Tampa Florida Matthew A. Jaro