Erlang Code Examples

Code examples in the ErlangLanguage.

Erlang was first implemented as a dialect of PrologLanguage, which is how it got most of its syntax (one of many exceptions being the nifty ErlangBitSyntax).


Here is a module defining a simple recursive function, illustrating simple pattern matching and guards:

 -module(math).
 -export([factorial/1]).

factorial(0) -> 1; factorial(X) when X > 0 -> X * factorial(X-1).


The BowlingGame, complete with tests. Illustrates more pattern matching, tuples such as {1,2} and lists such as [1,2,3].

Capitalised symbols are variables. Assignment to a constant (or an already bound variable, as Erlang is a SingleAssignmentLanguage) is actually a pattern match.

Matching [H|T] breaks a list into its first and remaining elements (Head and Tail).

 -module(bowling).
 -export([test/0,score/1]).
 -import(lists,[duplicate/2]).

test() -> 0 = score(duplicate(10,{0,0})), 60 = score(duplicate(10,{3,3})), 21 = score([{4,6},{3,5}|duplicate(8,{0,0})]), 23 = score([{4,6},{5,3}|duplicate(8,{0,0})]), 26 = score([{10,pass},{5,3}|duplicate(8,{0,0})]), 15 = score(duplicate(9,{0,0}) ++ [{4,6},{5,nothrow}]), 18 = score(duplicate(9,{0,0}) ++ [{10,pass},{5,3}]), ok.

score(Frame) -> score(Frame,1,0).

score([{10,_}|T], 10, Total) -> Total + 10 + element(1,hd(T)) + element(2,hd(T)); score([{First,Second}|T], Turn, Total) when First==10 -> score(T, Turn+1, Total+10+element(1,hd(T))+element(2,hd(T))); score([{First,Second}|T], Turn, Total) when First+Second==10, Turn==10 -> Total + 10 + element(1,hd(T)); score([{First,Second}|T], Turn, Total) when First+Second==10 -> score(T, Turn+1, Total+10+element(1,hd(T))); score([{First,Second}|T], Turn, Total) -> score(T, Turn+1, Total+First+Second); score([], _Turn, Total) -> Total.


An echo server. It works fine as long as you don't interrupt it. If you interrupt it, it doesn't release the socket, so there's some more work to do.

 -module(echo).
 -export([start/1,server/1,handle_messages/1]).

start(Port) -> spawn(?MODULE,server,[Port]).

server(Port) -> {ok, Socket} = gen_tcp:listen(Port,[{packet,line}]), listen(Socket).

listen(Socket) -> {ok, Active_socket} = gen_tcp:accept(Socket), Handler = spawn(?MODULE,handle_messages,[Active_socket]), ok = gen_tcp:controlling_process(Active_socket, Handler), listen(Socket).

handle_messages(Socket) -> receive {tcp,error,closed} -> done; {tcp,Socket,Data} -> gen_tcp:send(Socket,Data), echo:handle_messages(Socket); _Other -> unexpected end.

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