Erlang

ch13.erl

-module (ch13).
-compile(export_all).

timer() ->
	% io:format("Hi from ~p~n", [self()]),
	receive
		_ 
			-> 	io:format("Bye!~n"),
				exit('Bye')
	after
		5000
			-> 	%io:format("I'm still running~n"),
				timer()
	end.

timerJob() ->
	[
		{spawn(ch13, timer, []), ch13, timer},
		{spawn(ch13, timer, []), ch13, timer},
		{spawn(ch13, timer, []), ch13, timer},
		{spawn(ch13, timer, []), ch13, timer},
		{spawn(ch13, timer, []), ch13, timer},
		{spawn(ch13, timer, []), ch13, timer},
		{spawn(ch13, timer, []), ch13, timer},
		{spawn(ch13, timer, []), ch13, timer},
		{spawn(ch13, timer, []), ch13, timer},
		{spawn(ch13, timer, []), ch13, timer},
		{spawn(ch13, timer, []), ch13, timer}
	].

loopty_loop() ->
	receive
		{'DOWN', _Ref, process, Pid, Why} ->
			{Mod, Fun} = get(Pid),
			io:format("Spawning ~p after ~p~n", [Pid, Why]),
			erase(Pid),
			P = spawn(Mod, Fun, []),
			put(P, {Mod, Fun}),
			monitor(process, P);
		get ->
			io:format("~p~n", [get()])
	end,
	loopty_loop().

multivizier(WorkerList) ->
	lists:map(fun
		({Pid, Mod, Fun}) ->
			monitor(process, Pid),
			put(Pid, {Mod, Fun})
	end, WorkerList),
	loopty_loop().

lecture_notes.md

Erlang Lecture Notes

Error Handling

try FuncOrExpressionSeq of
  Pattern1 [when Guard1] -> Expressions1;
  Pattern2 [when Guard2] -> Expressions2;
  ...
catch
  ExceptionType1: ExPattern1 [when ExGuard1] -> ExExpressions1;
  ExceptionType2: ExPattern2 [when ExGuard2] -> ExExpressions2;
  ...
after
  AfterExpressions
end

ExceptionTypes are throw/1, error/1 and exit/1.

Shorthand:

try F
catch _:_ -> SaveExpression
after Cleaning

Ultimate shorthand, which ignores error/1 and exit/1 and behaves like catch _ -> ...:

catch F

Example

[{I, (catch 
  (fun
    (X) when is_number(X) -> X 
  end)(I))
} || I <- [1, "error"]].

It is also useful to get stack traces. Erlang way is to fail noisy and polite. Give a full information to a programmer but hide from a user.

Interfacing techniques

Erlang has multiple ways to interact with non-Erlang world:

• Start a process outside ERTS(using port). This solution requires to define a protocol and write a driver in your language of choice.
• Run a shell command, something like os:cmd('ls -al').
• Run the code inside a virtual machine. This solution also got multiple choices:
  • Linked-in drivers. Similar to port, but requires some additional code. It can make a use of additional support like threading and message sending.
  • NIF(native implemented functions). Piece of synchronous code, must be small and fast. Like BIFs from standard library.
  • C-Nodes. C nodes are nodes implemented in C that obey the Erlang distribution protocol. A “real” distributed Erlang node can talk to a C-node and will think that the C-node is an Erlang node (provided it doesn’t try to do anything fancy on the C-node like sending it Erlang code to execute).

strfun.erl

-module (strfun).
-export ([search/2]).

search(Pattern, Str) when is_list(Str), is_list(Pattern) ->
  search_acc(Pattern, Str, 0).
search_acc([C|Pattern], [H|T], Pos) ->
  if
    C =:= H ->
      search_acc(Pattern, T, Pos);
    true ->
      search_acc([C|Pattern], T, Pos + 1)
  end;
search_acc(Pattern, [], _) when is_list(Pattern) ->
  -1;
search_acc([], String, Pos) when is_list(String) ->
  Pos.