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Erlang and Go, mostly
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Ray Toal committed May 24, 2016
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Expand Up @@ -100,7 +100,7 @@ <h2 class="fragment fade-in"style="color:black;margin-bottom:2.5em;font-size:30
</section>

<section>
<h2 data-transition="fade">A Better Way</h2>
<h2 data-transition="fade">Hoare&rsquo;s Seven Proposals</h2>
<ol>
<li class="fragment fade-in">Parallel command launches procs simultaneously
<li class="fragment fade-in">Simple input and output commands
Expand All @@ -112,16 +112,19 @@ <h2 data-transition="fade">A Better Way</h2>
</ol>
</section>

<section>
<code>
First examples TODO
</code>
</section>
<section data-transition="convex">
<pre style="font-size:24pt">
[cardreader?card || lineprinter!line]

<section>
<code>
First examples TODO
</code>
[west::DISSASEMBLE || X::SQUASH || east::ASSEMBLE]

[ room::ROOM
|| fork(i:0..4)::FORK
|| phil(i:0..4)::PHIL
]

X :: *[c:character; west?c -> east!c]
</pre>
</section>

<section>
Expand All @@ -132,59 +135,82 @@ <h2>CSP the &ldquo;language&rdquo;</h2>
<li class="fragment fade-in">Rejection of asychronous buffers
<li class="fragment fade-in">Very static...Names and sizes of
processor arrays specified in advance
<li class="fragment fade-in"><em>Later, CSP became a process algebra</em>
</ul>
<p class="fragment fade-in"><em>Later, CSP became a process algebra</em></p>
</section>

<section>
<h2>Syntax</h2>
<code>
Command ::= skip | Var ':=' Exp
| Proc '?' Exp | Proc '!' Exp
|
</code>
</section>

<section>
<h2>Examples</h2>
</section>

<section>
<code>
...
</code>
<pre>
CmdList ::= (Decl ';' | Cmd ';')* Cmd
Cmd ::= 'skip' | Assn | In | Out | Alt | Loop | Parallel
Parallel ::= '[' Proc ('||' Proc)* ']'
Proc ::= Label? CmdList
Label ::= id (Sub (',' Sub)*)? '::'
Sub ::= Primary | Range
Primary ::= num | id
Range ::= id ':' Primary '..' Primary
Assn ::= Var ':=' Exp
Exp ::= num | str | id | id? '(' (Exp (',' Exp)*)? ')'
Var ::= id | id? '(' (Var (',' Var)*)? ')'
In ::= Name '?' Var
Out ::= Name '!' Exp
Name ::= Id ('(' Exp (',' Exp)* ')')?
</pre>
</section>

<section>
<code>
...
</code>
</section>
<h2>Terms</h2>
<pre style="font-size:26pt">
17
"string"
n
person("alice",age)
employee("bob",home("pasadena","ca","usa"))
P()
(x, y)
cons(a,100)
</pre>
</section>

<section>
<h2>Expressions and Assignments</h2>
<h2><s style="color:#777">Assignments</s> Matching</h2>
<pre style="font-size:26pt">
n := n * 2 + 1
a := cons(100, a)
p := person(name, age)
person(name, age) := q
person(name, 29) := person(alice, 29)
person(name, age) := person("alice", 29)
c := P()
P() := c
e := employee(bob, city(pasadena, ca, usa))
e := player(class(3), loc(88,173))
(x,y) := (y,x)
</pre>
<small>To match, must have same structure and same type. Assignment fails if no match.</small>
</section>

<section>
<h2>Input and Output</h2>
<pre>
...

</pre>
<small>Wait for each other. Must match. Assigns. Fails if other side already terminated.</small>
</section>

<section>
<code>
<h2>Alternative (Conditional)</h2>
<pre>
...
</code>

</pre>
</section>

<section>
<code>
<h2>Repetition (Loop)</h2>
<pre>
...
</code>

</pre>
</section>


Expand All @@ -200,15 +226,99 @@ <h2>Hoare&rsquo;s Suggestion</h2>
<h2>So...Who uses this stuff today?</h2>
</section>

<section>
<section data-transition="zoom">
<img src="erlang-logo.jpg" style="border:0">
</section>

<section data-background="hellojoe.jpg">
<div style="color:black">
<h2 style="color:black">Well, sort of...</h2>
<ul>
<li class="fragment fade-in">The sender names the receiver but not vice-versa
<li class="fragment fade-in">All communication is asynchronous
<li class="fragment fade-in">To make it synchronous, pass your process id to the receiver then wait on a response
</ul>
</div>
</section>

<section data-background="#B83998">
<p>Warning: Hacky, Inefficient Example</p>
<small>Just to show a wee bit of Erlang</small>
<pre><code class="hljs">main(_) ->
Max = 1000,
Printer = spawn(printer, print_server, []),
Counter = spawn(counter, run, [self(), Max-1]),
lists:foreach(
fun (N) ->
spawn(prime_printer, print_if_prime, [N, Printer, Counter])
end,
lists:seq(2, Max)),
receive done -> io:format("done~n") end.</code></pre>
</section>

<section data-background="#B83998">
<p>Not a good idea<p>
<small>Perhaps a good example tho</small>
<pre><code class="hljs">-module(prime_printer).
-export([print_if_prime/3]).

print_if_prime(N, Printer, Counter) ->
(fun Check(D) ->
if
D * D > N ->
Printer ! N,
Counter ! decrement;
N rem D == 0 ->
Counter ! decrement;
true ->
Check(D+1)
end
end)(2).
</code></pre>
</section>

<section data-background="#B83998">
<p>A super generic printer</p>
<small>Yep, I&rsquo;m a server!</small>
<pre><code class="hljs">-module(printer).
-export([print_server/0]).

print_server() ->
receive
N ->
io:format("~p ", [N]),
print_server()
end.
</code></pre>
</section>

<section data-background="#B83998">
<p>Here&rsquo;s that counter</p>
<pre><code class="hljs">-module(counter).
-export([run/2]).

run(Observer, 0) ->
Observer ! done;
run(Observer, N) ->
receive
decrement -> run(Observer, N-1)
end.
</code></pre>
<small>You didn&rsquo;t think Erlang had loops, did you?</small>
</section>


<section>
<img src="go-logo.png" style="border:0">
<h2>Who else?</h2>
</section>

<section data-background="#eeeeee" data-transition="zoom">
<img src="go-logo.png" style="border:0;box-shadow:none">
</section>

<section>
<section data-background="#152a8b">
<p>But with channels, not named processes</p>
<p>Channels are synchronous (by default)</p>
<pre><code class="hljs">
package main

Expand All @@ -223,7 +333,8 @@ <h2>So...Who uses this stuff today?</h2>
</code></pre>
</section>

<section>
<section data-background="#152a8b">
<p>You can have a buffered channel, too</p>
<pre><code class="hljs">
func generateMessages(ch chan string, n int) {
for i := 0; i < n; i++ {
Expand All @@ -242,7 +353,8 @@ <h2>So...Who uses this stuff today?</h2>
</code></pre>
</section>

<section>
<section data-background="#152a8b">
<p>Concurrent Sieve! (by Rob Pike, I think)</p>
<pre><code class="hljs">
func generate(first chan<- int) {
for i := 2; ; i++ {
Expand Down Expand Up @@ -273,6 +385,10 @@ <h2>So...Who uses this stuff today?</h2>
</code></pre>
</section>

<section data-background="white">
<p>http://divan.github.io/posts/go_concurrency_visualize/</p>
<img src="sieve.png" style="box-shadow:none">
</section>

<section>
<h2>CSP in Go</h2>
Expand All @@ -282,12 +398,20 @@ <h2>CSP in Go</h2>
</section>

<section>
<h2>Thanks to</h2>
<p>
<img src="yahoo-logo.png" style="border:none" height=150>
<img src="pwl-logo.jpeg" style="border:none;margin-left:2em" height=150>
</p>
<p>and @cateches</p>
<h2>Wrap Up</h2>
<ul>
<li class="fragment fade-in">Originally a language, later a process algebra
<li class="fragment fade-in">No shared memory, just message passing
<li class="fragment fade-in">Synchronous, unbuffered, named sender and receiver
<li class="fragment fade-in">Influence on Erlang, Go, many other languages
<li class="fragment fade-in">You should check out the <em>Go visualizations</em> and <em>CSP in Go</em>
<li class="fragment fade-in">Start thinking concurrently. And reread the paper.
</ul>
</section>

<section data-background="white">
<h2 style="margin-bottom:1.25em">Thanks to</h2>
<p><img src="yahoo-logo.png" style="border:none" height=70><br>and<br><img src="pwl-logo.jpeg" style="border:none" height=150><br>and @cateches</p>
</section>

</div>
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