Learn Erlang in One Video
In this tutorial I’m going to teach the core syntax of the Erlang language with many examples. This video is for someone that already knows another language and wants to translate common programming syntax into Erlang.
If you jump to YouTube in the description you’ll find time stamps to every main part of the video. For best results take notes on the cheat sheet provided below as you watch and leave any questions you have.
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Code & Cheat Sheet
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-module(erlangtut). -export([hello_world/0]). hello_world() -> io:fwrite("hello, world\n"). cd("/Users/derekbanas/Documents/workspace/ErlangTut/src"). c(erlangtut). erlangtut:hello_world(). cd("C:\Users\derekbanas\workspace\ErlangTut\src"). % @author derekbanas % @doc @todo Add description to erlangtut. % ----- BASICS ----- % Modules contain many functions % This will always be the first statement in a file % because it defines the module % We compile to byte code like this c(tut). -module(tut). % Import string functions -import(string, [len/1, concat/2, chr/2, substr/3, str/2, to_lower/1, to_upper/1]). % Defines what functions can be called from this module % /0 defines that this function doesn't receive attributes % /2 defines that add recieves 2 % -export([hello_world/0, add/2, add/3, main/0]). -export([main/0]). % We execute functions like this tut:hello_world(). % fwrite outputs a string to the console hello_world() -> io:fwrite("Hello World\n"). % Recieve 2 values and return the sum add(A, B) -> % You can call other functions % Separate multiple statements with a comma hello_world(), A + B. % You can define functions with the same name % as long as the number of attributes differ add(A, B, C) -> A + B + C. % tut:module_info(). gives you info on your module % ----- VARIABLES ----- % Variable names start with an uppercase letter % or _ and then letters, numbers, _, or @ % A variables value cannot change % A variables type is defined dynamically % You can call a function before it was created % Even if you call multiple functions only % output from the last shows main() -> var_stuff(), atom_stuff(), do_math(5,4), compare(4,4.0), what_grade(10), say_hello(german), string_stuff(), tuple_stuff(), list_stuff(), lc_stuff(), type_stuff(), find_factorial(3), sum([1,2,3]), sum2([1,2,3], 0), for(3,1), map_stuff(), record_stuff(), do_math2(), fun_stuff("Derek"), fun_stuff2(), write_txt("Write to the file"), write_txt2(" More text for the file"), read_txt(), error_stuff(0), read_txt2(), macro_stuff(5,6), spawner(), spawner(), spawner2(50,1), spawner2(100, 51). var_stuff() -> Num = 1, Num. % An Atom is variable thats name equals its value % They start with lowercase letters, or are % surrounded by single quotes atom_stuff() -> 'An Atom'. % ----- MATH ----- do_math(A, B) -> A + B, A - B, A * B, % Float division A / B, % Integer division A div B, % Modulus returns the remainder A rem B, % e raised to the X power math:exp(1), % Natural log math:log(2.71828), % Common log math:log10(1000), % Power math:pow(10,2), % Square root math:sqrt(100), % There is also sin, cos, tan, asin, acos, atan, % sinh, cosh, tanh, asinh, acosh, atanh % Generate random number from 1 to 10 random:uniform(10). % ----- COMPARING VALUES ----- % You receive true or fale from comparisons % 0 isn't equal to false compare(A, B) -> % Check for equality of value and type A =:= B, % Check for inequality of value and type A =/= B, % Disregard type A == B, % Disregard type A /= B, % >, <, >=, =<, and, or, not, xor Age = 18, (Age >= 5) or (Age =< 18). % ----- IF CONDITIONALS ----- % If is used to perform different actions % based on conditions preschool() -> 'Go to preschool'. kindergarten() -> 'Go to kindergarten'. grade_school() -> 'Go to grade school'. what_grade(X) -> if X < 5 -> preschool() ; X == 5 -> kindergarten() ; X > 5 -> grade_school() end. % ----- CASE CONDITIONALS ----- % Case performs different actions based on values say_hello(X) -> case X of french -> 'Bonjour'; german -> 'Guten Tag'; english -> 'Hello' end. % ----- STRINGS ----- % Strings must be surrounded by double quotes string_stuff() -> Str1 = "Random string", Str2 = "Another string", % You can place strings or any data in % output using ~p io:fwrite("String : ~p ~p\n", [Str1, Str2]), % format can be used for similar results Str3 = io_lib:format("It's a ~s and ~s\n", [Str1, Str2]), io:fwrite(Str3), % Get string length len(Str3), % Concatenate strings Str4 = concat(Str1, Str2), Str4, % Get index for character CharIndex = chr(Str4, $n), CharIndex, % Return string start at index and number % of characters Str5 = substr(Str4, 8, 6), Str5, % Get index of string StrIndex = str(Str4, Str2), StrIndex, % All uppercase to_upper(Str1), % All lowercase to_lower(Str1). % ----- TUPLES ----- % A Tuple can hold multiple values tuple_stuff() -> My_Data = {42, 175, 6.25}, % Get all values My_Data, % Store values in another tuple {A,B,C} = My_Data, % Return just 1 value C, % Use an anonymous variable to match a pattern {D,_,_} = My_Data, D, % You can use an Atom as the key for a value % Tagged Tuple My_Data_2 = {height, 6.25}, {height, Ht} = My_Data_2, Ht. % ----- LISTS ----- % Lists contain multiple values from any % data type list_stuff() -> List1 = [1,2,3], List2 = [4,5,6], % Join lists with ++ List3 = List1 ++ List2, List3, % Subtract a list List4 = List3 -- List1, List4, % Retrieve the 1st element (Head) hd(List4), % Retrieve all but the first (Tail) tl(List4), % Add a value to the list with the cons operator List5 = [3|List4], List5, % Get the head and tail [Head|Tail] = List5, Head. % ----- LIST COMPREHENSIONS ----- % List comprehensions make it easy to manipulate lists lc_stuff() -> List1 = [1,2,3], % Multiply every list item times 2 % N is an incrementing list item List2 = [2*N || N <- List1], List2, % You can add conditions like to get only evens List3 = [1,2,3,4], List4 = [N || N <- List3, N rem 2 == 0], List4, % Search through a list of tuples for perfect weather City_Weather = [{pittsburgh, 50}, {'new york', 53}, {charlotte, 68}, {miami, 78}], Great_Temp = [{City, Temp} || {City, Temp} <- City_Weather, Temp >= 50], Great_Temp. % ----- TYPE CONVERSIONS ----- type_stuff() -> % You can check the type of a variable is_atom(name), is_float(3.14), is_integer(10), is_boolean(false), is_list([1,2,3]), is_tuple({height, 6.24}), % You can convert from one to another using % type_to_type % atom_to_binary, atom_to_list, binary_to_atom, % binary_to_list, bitstring_to_list, binary_to_term, % float_to_list, fun_to_list, integer_to_list, % integer_to_list, iolist_to_binary, iolist_to_atom, % list_to_atom, list_to_binary, list_to_bitstring, % list_to_float, list_to_integer, list_to_pid, % list_to_tuple, pid_to_list, port_to_list, ref_to_list, % term_to_binary, term_to_binary, tuple_to_list List1 = integer_to_list(21), List1. % ----- RECURSION ----- % Recursion is the act of a function calling itself % Those things you normally accomplish with looping % in other languages are done using recursion % with Erlang % We can use recursion to find the factorial factorial(N) when N == 0 -> 1; factorial(N) when N > 0 -> N * factorial(N - 1). find_factorial(X) -> Y = factorial(X), io:fwrite("Factorial : ~p\n", [Y]). % 1st: 3 -> 3 * f(2) == 3 * 2 = 6 % 2nd: 2 -> 2 * f(1) == 2 * 1 (Send Above) % 3rd: 1 -> 1 * f(0) == 1 * 1 (Send Above) % Sum a list sum([]) -> 0; sum([H|T]) -> H + sum(T). % sum([1,2,3]) % 1 + sum([2,3]) % 1 + 2 + sum([3]) % 1 + 2 + 3 + sum([]) % Tail Recursive % Instead of holding up the additions % we can keep a running count sum2([], Sum) -> Sum; sum2([H|T], Sum) -> io:fwrite("Sum : ~p\n", [Sum]), sum2(T, H + Sum). % sum2([1,2,3], 0) % sum2([2,3], 1) % sum2([3], 3) % sum2([], 6) % You can create a for loop with recursion for(0,_) -> ok; for(Max,Min) when Max > 0 -> io:fwrite("Num : ~p\n", [Max]), for(Max-1,Min). % for(3,1) Num : 3 % for(2,1) Num : 2 % for(1,1) Num : 1 % for(0,1) End % ----- MAPS ----- % A Map is a group of key value pairs map_stuff() -> Bob = #{f_name=>'Bob', l_name=>'Smith'}, % Get value assigned to a key io:fwrite("1st Name : ~p\n",[maps:get(f_name, Bob)]), % Get all keys io:fwrite("~p\n", [maps:keys(Bob)]), % Get all values io:fwrite("~p\n", [maps:values(Bob)]), % Return everything except the key designated io:fwrite("~p\n", [maps:remove(l_name, Bob)]), % Check if a key exists maps:find(f_name, Bob), % Add a key value to the map maps:put(address, "123 Main", Bob). % ----- RECORDS ----- % You can define a custom type that contains % multiple fields -record(customer, {name = "", bal = 0.00}). record_stuff() -> % Define a customer Sally = #customer{name="Sally Smith", bal=100.00}, % Change data Sally2 = Sally#customer{bal = 50}, % Output data io:fwrite("~p owes $ ~p\n", [Sally2#customer.name, Sally2#customer.bal]). % ----- HIGHER ORDER FUNCTIONS ----- % Functions that can receive other functions as % a parameter is known as a higher order function % Define a function that multiplies % every item by 2 double(X) -> X * 2. % This one triples the number triple(X) -> X * 3. % lists:map takes a function and applies % that function to every item in the list % Fun is used to assign a function % to a variable do_math2() -> lists:map(fun double/1, [1,2,3]), lists:map(fun triple/1, [1,2,3]). % You can use fun to define anonymous functions fun_stuff(N) -> Fun_Stuff = fun() -> io:fwrite("Hello ~p\n",[N]) end, Fun_Stuff(). % You can also access values outside of the function fun_stuff2() -> X = 3, Y = 4, Z = fun() -> io:fwrite("Sum : ~p\n",[X + Y]) end, Z(). % ----- FILE I/O ----- % Create and write to a file write_txt(N) -> % Get file handler and write {ok, Fh} = file:open("MyFile.txt", [write]), % Write the text file:write(Fh, N). write_txt2(N) -> % Get file handler and append {ok, Fh} = file:open("MyFile.txt", [append]), file:write(Fh, N). % Read from file read_txt() -> % Get read permission {ok, File} = file:open("MyFile.txt", [read]), % Read text from file Words = file:read(File, 1024 * 1024), io:fwrite("~p\n", [Words]). % ----- EXCEPTION HANDLING ----- % Exception handling allows our program to % handle errors rather then just crashing % You place code that could crash after % try and then list what happens when certain % errors occur after catch error_stuff(N) -> try Ans = 2 / N, Ans catch error:badarith -> "Can't divide by zero" end. read_txt2() -> try {ok, File} = file:open("MyFile1.txt", [read]), Words = file:read(File, 1024 * 1024), io:fwrite("~p\n", [Words]) catch % This will catch all errors _:_ -> "File Doesn't Exist" end. % ----- MACROS ----- % Macros provide for inline code replacement % Define the constant and what replaces it -define(add(X,Y), {X+Y}). macro_stuff(X,Y) -> % ? defines to use the macro io:fwrite("~p\n", [?add(X,Y)]). % ----- CONCURRENCY ----- % Concurrency is the when several processes % execute at the same time and potentially % interact % As long as the processes aren't dependent % on each other they can run at the same time % Count to 1 million, calculate Pi aren't dependent % but start engine drive car are get_id(M) -> io:fwrite("ID : ~p\n", [M]). % You can generate a process and define the function % to execute. This passes the process ID spawner() -> spawn(fun() -> get_id([self()]) end). % Create a for loop that counts using different % ranges for2(0,_) -> ok; for2(Max,Min) when Max > 0 -> io:fwrite("Num : ~p\n", [Max]), for(Max-1,Min). % The process take turns doing their jobs spawner2(Max, Min) -> spawn(fun() -> for2(Max, Min) end). |
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