From 7910e2910daa33af41cef729dcf2408a106473de Mon Sep 17 00:00:00 2001 From: Guido Günther Date: Tue, 10 May 2016 17:20:10 +0200 Subject: Add html version --- erlang.html | 415 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 415 insertions(+) create mode 100644 erlang.html diff --git a/erlang.html b/erlang.html new file mode 100644 index 0000000..d363274 --- /dev/null +++ b/erlang.html @@ -0,0 +1,415 @@ + + + + + + + + Wissenswertes über Erlang + + + + + + + + + + + +
+
+ +
+

Wissenswertes über Erlang

+

Guido Günther

+

2016-05-09

+
+ +
+

Who am I

+
    +
  • Free Software Hacker (Freelancing Software Developer)
    • +
  • Debian Developer since 2000
    • +
  • Contributed to libvirt-*, X11, Linux Kernel, GNOME, Calypso, …
    • +
  • FSFE Fellow and GNOME Foundation member
    • +
  • Rather new to Erlang
    • +
+
+
+

Erl-what?

+
    +
  • Developed at Ericsson in 1986
    • +
  • Open sourced 1998
    • +
  • Ericsson Language or Agner Krarup Erlang?
    • +

  • For telephone systems

    • +
  • Functional, concurrent programming language
    • +
  • Garbage collected runtime system
    • +

  • Erlang/OTP

    • +
+
+
+

Erlang, Features

+
    +
  • Fault tolerant
    • +
  • Hot code replacements
    • +
  • Distributed
    • +
  • highly available - 12 years of uptime - nine 9s (30 ms / a)
    • +
+
+
+

Projects

+
    +
  • ejabberd, Riak, CouchDB, RabbitMQ
    • +
  • WhatsApp, GitHub, Facebook, …
    • +
+
+
+

You lack style - no, state!

+
+
+ +

Functional language

+

f(x) = y

+
+
+ +

i = i + 3

+
+
+ +

i = i + 3

+
+
+ +

for (int i=0; i < 3; i++) do_something(i);

+
+
+ +

for (int i=0; i < 3; i++) do_something(i);

+
+
+ +
1> A=3.
+3
+2> A=4.
+** exception error: no match of right hand side value 4
+
+
+ +

No means No

+
    +
  • No imperative programming
    • +
  • No global variables and state
    • +
  • No pointers
    • +
  • No variable reassignments
    • +
+
+
+ +
    +
  • Yes, Higher Order Functions
    • +
  • Yes, Pattern Matching
    • +
  • Yes, Code Reloads
    • +
  • Yes, Lots of independent Processes
    • +
+
+
+ +

Recursion to the Rescue

+
loop(X) -> loop(X, 0).
+
+loop(X=0, Sum) -> Sum;
+loop(X, Sum)   -> loop(X-1, Sum+X).
+
+
+ +

Recursion in Detail

+
loop(3)   -> loop(3, 0)
+loop(3,0) -> loop(3-1, 0+3)
+loop(2,3) -> loop(2-1, 3+2)
+loop(1,5) -> loop(1-1, 5+1)
+loop(0,6) -> 6
+
+3 + 2 + 1 = 6
+
+
+ +

Head to Wall Tail

+
A = [this, is, a, list].
+[H|T] = A.
+
+
+ +
rev(L) -> rev(L, []).
+
+rev([],    N) -> N;
+rev([H|T], N) -> rev(T, [H] ++ N).
+
+
+ +
rev([a,b,c,d])       -> rev([a,b,c,d],      [])
+
+rev([a|[b,c,d]], []) -> rev([b,c,d], [a] ++ [])
+
+rev([b|[c,d]],  [a]) -> rev([c,d],  [b] ++ [a])
+
+rev([c|[d]],  [b,a]) -> rev([d],  [c] ++ [b,a])
+
+rev([d|[],  [c,b,a]) -> rev([], [d] ++ [c,b,a])
+
+rev([],   [d,c,b,a]) -> [d,c,b,a]
+
+
+ +

More pattern matching

+
A = {this, is, a, tuple}.
+{_, _, _, B} = A.
+
+
+ +
> B.
+tuple
+> _.
+* 1: variable '_' is unbound
+
+
+ +

Fun with Funs

+
F = fun (X) -> X*X end.
+> F(3).
+> F(ok).
+
+
+ +
> F(3). 
+9
+> F(ok).
+** exception error: an error occurred when evaluating an arithmetic expression
+     in operator  */2
+       called as ok * ok
+
+
+ +

Success, Typing!

+

Dialyzer

+
-spec foobar(atom()) -> [atom()].
+foobar(App) -> …
+
+
+

Processes, which Processes

+
+
+ +

Spawning a process

+
F = fun(X) -> io:format("~p~n", [X]) end.
+times(X, Args, C) -> ...
+
+spawn(l, times, [F,  "I'm a process", 3]).
+
+
+ +
spawn(l, times, [F,  "I'm a process", 3]),
+spawn(l, times, [F, "I'm a process too", 3]).
+
+
+ +

Concurrency for free!

+
"I'm a process"
+"I'm a process too"
+"I'm a process"
+"I'm a process too"
+<0.53.0>
+"I'm a process"
+"I'm a process too"
+
+
+ +

Share(d) nothing

+
start_pong(Pid) -> …
+pong(Pid) -> …
+
+> P = l:start_pong(self()).
+> P ! { ping, "foo" }.
+> P ! giveup.
+
+
+ +
> R = fun () -> receive M -> M end end.
+
+
+ +
> R().
+{pong,"hallo1"}
+> R().
+{pong,"hallo2"}
+
+
+ +

Let it crash

+
2> P ! {ping, 3}.
+{ping,3}
+3> 
+=ERROR REPORT==== 8-May-2016::15:13:30 ===
+Error in process <0.34.0> with exit value:
+{badarg,[{io,format,[<0.25.0>,"pong: Received ping '~s'~n",[3]],[]},
+         {l,pong,1,[{file,"l.erl"},{line,57}]}]}
+
+
+ +
2> P ! whatever
+Unknwown message asfasdf, giving up
+
+
+ +

Linking processes

+
> process_flag(trap_exit, true).
+> P = l:start_pong2(self()).
+3> P ! sadfsadf.
+Unknwown message sadfsadf, giving upsadfsadf
+4> receive X -> X end.
+{'EXIT',<0.35.0>,reason}
+
+
+ +

Distributed nodes

+
$ erl -sname ping
+$ erl -sname pong
+
+register(spawn(...))
+
+
+ +

On pong

+
> P = l:start_pong3().
+

On ping

+
> {pong, pong@bogon} ! {ping, "hello", self()}.
+> {pong, pong@bogon} ! {ping, "hello", self()}.
+> receive X -> X end.
+{pong,"hello"}
+
+
+ +
erlang:node().
+erlang:nodes().
+
+
+ +

Hot code replacements

+
version() -> …
+c(l).
+
+
+

OTP

+

Open Telecommunication Platform

+
+
+ +

Batteries inclued

+
    +
  • EUnit
    • +
  • Mnesia
    • +
  • HTTP/SNMP/…
    • +
  • …
    • +
+
+
+ +

Behaviours

+
    +
  • gen_{server,fsm,event}
    • +
  • supervisor
    • +
  • application
    • +
+
+
+

Debugging

+
+
+ +

Tracing Processes, Messges, …

+
erl -sname observer -hidden  -run observer
+
+
+ +

Tracing functions

+
dbg:start().
+dbg:tracer().
+% trace messages (m)
+dbg:p(pong, m).
+
+
+

The greater Erlang Universe

+ +
+
+

Extending Erlang

+
+
+ +

NIFs - Gesundheit!

+

Native Implemented Functions

+
+
+ +

C-Nodes

+
+
+

See also

+ +
+
+

Further Reading

+ +
+
+

Questions?

+
+
+
+ + + + + + + -- cgit v1.2.3