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ocaml_presentation.html
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<head>
<meta charset="utf-8">
<title>OCaml Presentation Mon Jan 18, 2016</title>
<meta name="author" content="Edgar Aroutiounian">
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<div class="slides">
<section>
<p> OCaml Meetup, San Francisco</p>
<p> A Survey of OCaml for new and experienced
programmers </p>
<img src="mixrank-meetup-ocaml-01.png"></img>
<p>
<small>By <a href="http://twitter.com/edgararout">@edgararout</a></small>
</p>
</section>
<section>
<h1> About Me</h1>
<p> My name is Edgar Aroutiounian, I'm a programmer at
MixRank </p>
<ul>
<li> Have been actually paid for functional programming. </li>
<li>First introduced to OCaml in compiler's class at
Columbia University, but ignored it after that.
</li>
<li> Found it again when I started looking for a new
language that was fast, type safe, not verbose, not
Haskell.
</li>
<li>Now an OCaml fantatic, first non trivial OCaml
project was this space invaders
game
</li>
<img src="space_invader.gif"></img>
</ul>
</section>
<section>
<h2>What's to love</h2>
<ol>
<li> OCaml is a <em>real</em> functional programming
language; data is immutable by default and you can define
control flow by using functions. </li>
<li> You can run OCaml interactively, compile to JavaScript,
compile to bytecode, native code</li>
<li> No noisy type declarations everywhere</li>
<li> Emacs/Vim support is fantastic, merlin is a magician
after all</li>
<li> Standard Unix tools work well with it, gdb, etc </li>
<li> Monads when you need them, not forced on you.</li>
<li> Understandable execution model </li>
<li> On tons of platforms</li>
<li> Pragmatic, but never too far from research community </li>
</ol>
</section>
<section>
<h2> Famous users </h2>
<ul>
<li>OCaml is used at Jane Street, come to the next meetup to get
this t-shirt I'm wearing </li>
<li> Bloomberg, they just released another OCaml to
JavaScript compiler </li>
<li> Facebook, multitude of tools like flow and pfff </li>
<li> Ahrefs, entire backend is OCaml</li>
<li> Citrix, no idea but OCaml</li>
<li> Mirage OS, unikernel implemented in OCaml </li>
<li> MixRank let me write an iPhone port forwarder in
OCaml </li>
</ul>
<p> And of course there's more I haven't mentioned </p>
</section>
<section>
<h2>Jargon Crash course</h2>
<ul>
<li> ocamlopt is the native code compiler, ocamlc is
bytecode compiler, ocaml is the plain repl</li>
<li>utop is an enchanced repl, great for interactive
use </li>
<li>opam is the package manager</li>
<li> merlin provides code completion and typechecking in
your text editor </li>
</ul>
<p>...and there's much more, I recommend reading my blog
post <a href="http://hyegar.com/blog/2015/10/19/so-you're-learning-ocaml">here</a>
it will get you up to speed on everything OCaml tooling ecosystem
</p>
</section>
<!-- Start off with easy stuff -->
<section>
<h2>Code!</h2>
<p> Let's start with some easy stuff, sum up only the odds </p>
<pre>
<code class="ocaml">
List.fold_left begin fun running item ->
if item mod 2 = 0
then running
else running + item
end 0 [3;2;4;6;5;7;8;0;1];;
</code>
</pre>
</section>
<section>
<p> Okay that nice, how about some real code... </p>
<p> Real code will require the use of some libraries, </p>
<pre>
<code class="ocaml">
let rec walk_and_action action node =
if Sys.is_directory node
then (Sys.readdir node
|> Array.to_list
|> List.map (Filename.concat node)
|> Lwt_list.iter_p (walk_and_action action))
else action node
</code>
</pre>
<p> Explanation: Go over a directory, apply a function to a
file in the directory, if you find any directory then
recurse on it, btw do this all in parallel </p>
</section>
<section>
<p> And now something nontrivial ... </p>
<pre>
<code class="ocaml">
open Lwt.Infix
let addr = Unix.ADDR_INET (Unix.inet_addr_loopback, 5000)
let cleanup l : Yojson.Basic.json list =
l |> List.map begin fun a_line ->
let chopped =
Stringext.full_split a_line ~on:' ' |>
List.filter begin fun str ->
if str = " " then false else true
end |>
Array.of_list in
`Assoc [("USER", `String chopped.(0));
("PID", `Int (int_of_string chopped.(1)));
("COMMAND", `String chopped.(10))]
end
let program =
let server = Lwt_io.establish_server addr begin fun (ic, oc) ->
let command = Lwt_process.shell "ps aux" in
let stream = Lwt_process.pread_lines command in
(Lwt_stream.to_list stream >>= fun ps_output ->
let cleaned = cleanup (List.tl ps_output) in
cleaned |> Lwt_list.iter_s begin fun the_json ->
let to_string = Yojson.Basic.pretty_to_string the_json in
Lwt_io.write_from_string_exactly oc to_string 0 (String.length to_string - 1)
>>= fun _ -> Lwt_io.write_char oc '\n'
end
>>= fun _ -> Lwt_io.close oc)
|> Lwt.ignore_result
end
in
(* Lwt.wait gives you back (thread, waker) *)
(* since we don't want the server to ever stop *)
(* we throw away the wakener *)
Lwt.wait () |> fst
let () =
Lwt_main.run program
</code>
</pre>
<p> Explanation: Create a simple server that will give back
JSON that describes the some information about PS on the
server </p>
</section>
<section>
<p> Shameless plug, ...compile and run on node </p>
<pre>
<code class="ocaml">
open Nodejs
let _ =
Fs.create_read_stream "code.ml" >|>
Zlib.create_gzip () >|>
Fs.create_write_stream "NEWCODE_TEST.ml"
</code>
</pre>
</section>
<section>
Out of time, any questions?
</section>
</div>
</div>
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