Erlang Programming Examples

Maps

erlang

-module(helloworld).  
-export([start/0]).  
 
start() ->  
   Map1 = #{name => 'abc',age => 40, gender => 'M'},  
   io:fwrite("~w",[map_size(Map1)]).

Tuple

erlang

-module(helloworld).  
-export([start/0]).  

start() ->  
   K = {abc,50,pqr,60,{xyz,75}} ,  
   io:fwrite("~w",[tuple_size(K)]).

Bit String

erlang

-module(helloworld). 
-export([start/0]). 

start() -> 
   Bin2 = <<15,25>>, 
   P = binary_to_list(Bin2), 
   io:fwrite("~w",[P]).

Boolean

erlang

-module(helloworld). 
-export([start/0]). 

start() -> 
   io:fwrite(5 =< 9).

Atom

erlang

-module(helloworld). 
-export([start/0]). 

start()-> 
   io:fwrite(monday).

Number

erlang

-module(helloworld).
-export([start/0]). 
start() -> 
   io:fwrite("~w",[5+4]).

Function Overloading in Erlang

erlang

-module(helloworld).  
-export([addnum/2,addnum/3,start/0]).   

addnum(X,Y) ->  
   Z = X+Y,  
   io:fwrite("~w~n",[Z]).  
    
addnum(X,Y,Z) ->  
   A = X+Y+Z,  
   io:fwrite("~w~n",[A]).  
  
start() -> 
   addnum(5,5),     addnum(5,2,8).

Defining a Function in Erlang

erlang

-module(helloworld).  
-export([add/2,start/0]).   

add(A,B) ->
   C = A + B,  
   io:fwrite("~w~n",[C]).  
start() ->  
   add(5,6).

Compile and Execute Erlang Online

erlang

-module(helloworld).
-author('[email protected]').
-vsn('2018-10-28').
-export([tipp_kod/2]).
%-compile(export_all).

tipp_kod(Max, Tipp_S) -> 
	[H|T] = element(1, Tipp_S),
	Plus_one = lists:seq(1,Max,1) ++ [H|T],
	LZS = lista_zsak(Plus_one),
	F = lists:map(fun(X) -> X - 1 end, LZS),
	DUP = lists:duplicate(erlang:length(F),erlang:length([H|T])),
	rek(DUP, F, element(2, Tipp_S)).
	

lista_zsak([]) -> [];
lista_zsak(L) -> [M || E <-lists:usort(L), M <- [count_element(L,E)]].

rekurzio([],[],K) -> 
	case K == 0 of
		true -> [[]];
		false -> []
	end;
rekurzio(H, L, K) ->
	case hd(H) < 0 of
		true -> [];
		false ->
			case K < 0 of
				true -> [];
				false -> 
					R = rekurzio([hd(H)-1|tl(H)], L, K),
					P = rekurzio(tl(H), tl(L), K-min(hd(H), hd(L))),
					Q = [[hd(H)|S] || S <- P], 
					lists:append(R,Q)
			end
	end.	

rek(H, _, K) when K > hd(H) -> [];
rek(H, L, K) when K == hd(H) -> perm(L,1,1);
rek(H, L, K) when K < hd(H) ->
	Zsak = get_lists(lists:sum(L), rekurzio(H,L,K)),
	append_all(Zsak).

append_all([]) -> [];
append_all(O) ->
	perm(hd(O),1,1) ++ append_all(tl(O)).

get_lists(Size, L) -> lists:filter(fun(X) -> lists:sum(X) =:= Size end, L).

% perm([2, 1, 2, 4], 1, 0).
perm([], _, _) -> [[]];
perm([1], N, _) -> [[N]];
perm(L, _, I) when erlang:length(L) < I -> [];
perm(L, N, I) ->
	case hd(L) == 0 of
		true -> 
			perm(tl(L), N+1, 1);
		false ->
			case lists:nth(I,L) == 0 of
				true -> 
					L1 = [],
					L2 = perm(L, N, I+1),
					L1 ++ L2;
				false ->
					{L1a,L1b} = lists:split(I-1,L),
					L1b2 = [hd(L1b)-1|tl(L1b)],		
					L1 = [[N+I-1|T] || T <- perm(L1a ++ L1b2, N, 1)],
					L2 = perm(L, N, I+1),
					L1 ++ L2
			end	
	end.

count_element([],_) -> 0;
count_element(L, E) -> 
	H = hd(L),
	if
		H == E -> R = 1 + count_element(L--[H], E);
	true ->
		R = count_element(L--[H], E)
	end,
	R.

Compile and Execute Erlang Online

erlang

%hello world program
-module(hello world).
-export([start/o]).
start()->
 io:fwrite("hello, world/n")

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