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Intro to Erlang

OJ Reeves. Intro to Erlang. Agenda. The Boring Stuff Basic syntax, expressions, funcs , records Atoms, BIFs, data types, bools , equality The not so Boring Stuff Pattern matching, guards, binaries Some Interesting Stuff processes, concurrency A Fun Problem Super Basic Webserver.

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Intro to Erlang

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  1. OJ Reeves Intro to Erlang

  2. Agenda • The Boring Stuff • Basic syntax, expressions, funcs, records • Atoms, BIFs, data types, bools, equality • The not so Boring Stuff • Pattern matching, guards, binaries • Some Interesting Stuff • processes, concurrency • A Fun Problem • Super Basic Webserver

  3. Play Along • Load werl or erl, that’s your REPL. • Modules? Create one for mucking around, foo.erl: • -module(foo). %% matches file-compile(export_all).%% your stuff goes here • Compile file in REPL: c(foo). • Your code is auto-loaded when compiled.

  4. The Boring Stuff • IQ = 10. %% “binding”IQ = 10. %% ok, same value boundIQ = 11. %% runtime error • Name = “OJ”. • Response = <<“{\”name\”:\”OJ\”}”>>. • Point = {1.0, 3.2}.{X, Y} = Point. • Tuples can be of mixed “type” / nested • random() -> 4. %% ode to XKCD • L = [“I am”, “a list of”, “strings”]. • Lists can be of mixed “type” • L2 = [1, 10.4, “fear me!”, my_atom].

  5. More Boring Stuff • clean(Text) -> • Funs = [fun rem_bad/1, fun add_punc/1],lists:foldl(fun(X, T) -> X(T) end, Text , Funs). • -record(person, {name, age, state=sober}). • get_name(#person{name=Name}) -> Name. • set_name(Person, Name) -> • Person#person{name=Name}. • Common return values: • ok vs {error, “Reason”} • ok = some_module:do_something().

  6. The Last of the Boring Stuff • Status = dead. • anything_like_this, ‘OR THIS’ • BIF – “Built in Function” • integer_to_list(), list_to_binary(), atom_to_list(), etc. • Data types – don’t really have any! • Boolean stuff • and, or, xor, andalso, orelse • Equality • =:= =/= (basically == and !=) • == /= (when mixed “types” such as 1 == 1.0) • <, =<, >=, >, etc(=< is not a typo!)

  7. The Not So Boring Stuff • Pattern matching! • div(N, 0) -> infinity; %% cont..div(N, D) -> N /D. • first_item_even([H|T]) -> H rem 2 =:= 0. • get_status(P) -> • case P#person.name of • “OJ” -> loser; %% continue_ -> legend %% no , or . • end. %% terminated here

  8. More Not So Boring Stuff • Pattern matching is binding! • rock, paper, scissors (no lizard/spock) • Winner = case {Move1, Move2} of • {paper, rock} -> player1; • {rock, scissors} -> player1; • {scissors, paper} -> player1; • {Move, Move} -> draw; %% oooh! • _ -> player2 • end. • Guards! • is_decrepit(#person{age=Age}) when Age > 80 -> true;is_decrepit(_Person) -> false.

  9. More Not So Boring Stuff • Binaries are special lists • <<“can have string data”>>. • <<3, 2, 5, 76>>. %% or int data • Can be pattern matched: • A = <<1, 2, 3, 4>>. • <<B, C, D, E>> = A. • C == 2 • <<F:4, G:8, H:20>> = A. • F = 0, G = 16, H = 131844. • Bit syntax – pull apart binaries!

  10. Last of the Not So Boring Stuff • Pulling an MP3 header apart: • valid_header(<<2#11111111111:11, B:2, C:2, _D:1, _E:4, _F:2, _G:1, _Bits:9>>) -> • case {B, C} of • {1, _} -> false; %% bad version{_, 0} -> false; %% bad layer_ -> true • end; • valid_header(_) -> false. • Thanks Joe!

  11. Interlude - Fizzbuzz • For each number from 1 to 100, output: • “Fizz” if divisible by 3 • “Buzz” if divisible by 5 • “FizzBuzz” if divisible by both 3 and 5 • The number itself otherwise.

  12. Some Interesting Stuff • Processes – very cheap, easy to spin up. Not “native”. • spawn(Fun) -> pid() • Spawn Fun/0 in a new process • spawn(Node, Fun) ->pid() • Spawn Fun/0 on the given node • spawn(Mod, Fun, Args) -> pid() • Spawn Mod:Fun(Args) in a new process • spawn(Node, Mod, Fun, Args) -> pid() • See if you can guess… • Also spawn_link() which links processes together. • Eg. Notification of crashing

  13. More Interesting Stuff • Send message to a process:Pid ! Message. • Message can be any Erlang term. • To receive a message:rec() -> • receive • pattern1 -> action1()… • pattern2 -> action2()… • after timeout -> • timeout_action(). • end. • Loop via recursive calls.

  14. More Interesting Stuff • Demo of echo(). • Parallel map: • spawn() for each “job” • Wait for response from each Pid • Combine results • Show me tehcodez.

  15. A Fun Problem • Create a “ring” of N processes. • Send a message around the ring. • Each node prints the message and forwards on to the next process. • If the message is quit, terminate the process. • Code!

  16. Super Basic Webserver • There is an API (inets), but we’ll do our own. • Listen on a port (8000). • When connection received, spawn a process to continue listening. • Use current process to handle request. • Support GET • Return 200 & content for valid URI. • Return 404 otherwise. • CODE!

  17. The End • That’s it. • There is no more. • Questions? • http://buffered.io/ • http://twitter.com/TheColonial

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