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<  Erlang  ~  learning - help correct this code
himadripalit
Posted: Fri Apr 24, 2009 11:45 am Reply with quote
Joined: 24 Apr 2009 Posts: 1
Hello All,

Can someone please tell me why cant I do something like this, I am totally new to erlang , this the stupid looking code:


Code:
-module(clientserver).
-export([client/1]).

client(N) ->
register(client,spawn(fun() -> receive_ans() end)),
server ! {double_of,N}.

receive_ans() ->
server(),
receive
 {answer,Result} -> {Result}
end.

server() ->
register(server,spawn(fun() -> loop() end)).

loop() ->
receive
{double_of,X} ->
   client ! {answer,X*2},
loop()
end.

after I compile  I get
c(clientserver).       
./clientserver.erl:14: Warning: function server/0 is unused
./clientserver.erl:18: Warning: function loop/0 is unused
{ok,clientserver}

and needless to say,I get an error on running as server/0 and loop/0 not getting recognised.

Update: I realised that server/0 wasnt getting called so put a call to server/0 in receive_ans(). Now it compiles but an error occurs on calling

Code:
clientserver:client(7).

** exception error: bad argument
     in function  clientserver:client/1


Thanks to keymone pointing it out, calling server() from receive_ans wasnt the right thing to do as this means creating a server process every time a client sends a request to the server.

Also he sent me the correct code, so here it is :

Code:
-module(clientser).
-compile(export_all).

client(N) ->
ClientPID = self(),
aserver ! {ClientPID, double_of, N},
receive {answer, R} -> R end.

server() ->
register(aserver, spawn(fun() -> loop() end)).

loop() ->
receive
{ClientPID, double_of, N} ->
ClientPID ! {answer, N*2},
loop()
end.


Before running it, the server needs to be started and voila!
Thanks keymone.


Last edited by himadripalit on Fri Apr 24, 2009 1:38 pm; edited 2 times in total
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keymone
Posted: Fri Apr 24, 2009 12:30 pm Reply with quote
User Joined: 17 Sep 2007 Posts: 11 Location: Lviv, Ukraine
-export([server/0]).
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