why is this function not compiling in Erlang - erlang

I'm a newbie in Erlang so stay with me.
I've got this function in erlang that I'm trying to compile, through the file animal.erl.
module(animal).
help_moi(Animal) ->
Talk = if Animal == cat -> "miaou";
Animal == beef -> "meuuuh";
Animal == dog -> "Wouf";
Animal == tree -> "treee!";
true -> "ezfezfezf,"
end, %blablabla%
{Animal ,"dit", ++ Talk ++ "!" }. %oh là là là%
I'm then compiling it with erl
c(animal).
And these the errors , I'm having
1> c(animal).
animal.erl:1: syntax error before: '.'
animal.erl:9: syntax error before: '++'
animal.erl:9: no module definition
error
I tried to look on google but not much documentations on it.
Any ideas?


The module directive starts with a - character:
-module(animal).
And you have an extra comma between "dit" and ++ Talk.
After fixing those two things, I get a warning, not an error:
animal.erl:2: Warning: function help_moi/1 is unused
You probably want to export the function, so you can call it from outside the module:
-export([help_moi/1]).

Related

What are the requirements for position of custom attributes in an Erlang module?

It seems:
Dialyzer and erlc both error when there is a user-defined attribute in a source file before -module
Shell session demonstrating:
~ cat sample.erl
-my_attr(my_value).
-module(sample).
-compile([export_all, nowarn_export_all]).
main(_) ->
ok.
~ erlc sample.erl
sample.erl:1:2: no module definition
% 1| -my_attr(my_value).
% | ^
~ dialyzer sample.erl
Checking whether the PLT /Users/mheiber/Library/Caches/erlang/.dialyzer_plt is up-to-date... yes
Proceeding with analysis...
dialyzer: Analysis failed with error:
Could not scan the following file(s):
/Users/mheiber/sample.erl:1:2: no module definition
Last messages in the log cache:
Reading files and computing callgraph...
Is the contract for order of user-defined attributes documented anywhere? Or is this a bug?
All I could find in the docs is that predefined attributes must come before function declarations:
https://www.erlang.org/doc/reference_manual/modules.html#pre-defined-module-attributes

-module(Module).
Module declaration, defining the name of the module. The name Module,
an atom, is to be same as the file name minus the extension .erl.
Otherwise code loading does not work as intended.
This attribute is to be specified first and is the only mandatory attribute.

Erlang exited with reason - undef (with string:find/2 func)

trying to use function string:find/2but every time getting the error
CRASH REPORT Process <0.779.0> with 0 neighbours exited with reason: {{undef,[{string,find,[[<<208,162,51,32,208,190,208,177,209,137,46,44,32,84,51,32,116,111,116,97,108,44>>],[<<208,186,209,128,208,190,208,178>>]],[]},{proxy_layer_cli_handle_req,do_execute_keysearch,4,[{file,\"/opt/proxy_layer/_build/test/lib/proxy_layer/src/proxy_layer_cli_handle_req.erl\"},{line,222}]},{proxy_layer_cli_handle_req,keysearch,3,[{file,\"/opt/proxy_layer/_build/test/lib/proxy_layer/src/proxy_layer_cli_handle_req.erl\"},{line,...}]},...]},...}
when i use it in terminal - everything is okay
1> string:find(<<208,162,51,32,208,190,208,177,209,137,46,44,32,84,51,32,116,111,116,97,108,44>>,<<208,186,209,128,208,190,208,178>>).
1> nomatch
I'm using Erlang 20.1
here is the code which I use:
do_execute_keysearch([First|Rest], PriceList, Keyword, Acc) ->
Id = utils:get_value(<<"Id">>, First),
case utils:get_value(<<"Keywords">>, First) of
<<>> -> do_execute_keysearch(Rest, PriceList, Keyword, Acc);
undefined -> do_execute_keysearch(Rest, PriceList, Keyword, Acc);
Keys ->
case string:find(Keys, Keyword) of
nomatch ->
do_execute_keysearch(Rest, PriceList, Keyword, Acc);
_ ->
Price = find_price_by_service_id(PriceList, Id),
NewAcc = [lists:append(Price, First) | Acc],
do_execute_keysearch(Rest, PriceList, Keyword, NewAcc)
end
end;
UPDATE:
Issue fixed after changing Erlang version in docker container. (Changed to Erlang 20.1)
Don’t know why there are some modules undefined in Erlang 19
So the problem solved now

string:find/2 was added to Erlang in version 20 which is why you were getting an undef error in Erlang 19. The solution is to upgrade to Erlang 20 (which you've already done).

Look at the error more carefully. Or rather, try to reproduce it. Which of these looks more like your error?
1> catch lists:nonexist(<<1>>, <<2>>).
{'EXIT',{undef,[{lists,nonexist,[<<1>>,<<2>>],[]},
{erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,674}]},
{erl_eval,expr,5,[{file,"erl_eval.erl"},{line,431}]},
{shell,exprs,7,[{file,"shell.erl"},{line,687}]},
{shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
{shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]}}
2> catch lists:nonexist([<<1>>], [<<2>>]).
{'EXIT',{undef,[{lists,nonexist,[[<<1>>],[<<2>>]],[]},
{erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,674}]},
{erl_eval,expr,5,[{file,"erl_eval.erl"},{line,431}]},
{shell,exprs,7,[{file,"shell.erl"},{line,687}]},
{shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
{shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]}}

Some error occurred concerning record in erlang when compile

I'm new to erlang, and here's my code:
-module(main).
-author("jasonzhu").
%% API
-export([new/2]).
-record(person, {name, age}).
new(Name, Age) ->
#person(name=Name, age=Age).
When compiling in prompt via erl main.erl, the following error occurred:
$ erlc main.erl
main.erl:20: syntax error before: '('
main.erl:13: function new/2 undefined
main.erl:15: Warning: record person is unused
Could anyone help me out? I didn't see any explicit culprit against my problem.
Thanks in advance.

On the last line it should be braces, not parentheses:
new(Name, Age) ->
#person{name=Name, age=Age}.
See the documentation on records for more information (and examples)

External function call Erlang

I'm trying to call a function (from an external module) in erlang. both beam files are located in the same directory.
-module(drop2).
-export([fall_velocity/1]).
fall_velocity(Distance) -> math:sqrt(2 * 9.8 * Distance).
Then I'm calling
-module(ask).
-export([term/0]).
term() ->
Input = io:read("Enter {x,distance} ? >>"),
Term = element(2,Input),
drop2:fall_velocity(Term).
it gives the following error.I tested individual modules for errors. it is compiling with out any errors or warning.
Eshell V5.10.2 (abort with ^G)
1> ask:term().
Enter {x,distance} ? >>{test,10}.
** exception error: an error occurred when evaluating an arithmetic expression
in function drop2:fall_velocity/1 (drop2.erl, line 3)
Not sure why it is throwing arithmetic expression error .

You could read the documentation to figure out that the result is {ok, Term}. You could try the io:read/1 function in the console, then you'd see following:
1> io:read("Enter > ").
Enter > {test, 42}.
{ok,{test,42}}
2>
That means that you need to deconstruct the result of io:read/1 differently, for example like this:
-module(ask).
-export([term/0]).
term() ->
{ok, {_, Distance}} = io:read("Enter {x, distance} > "),
drop2:fall_velocity(Distance).

Avoid NZEC error in Erlang in SPOJ

I've written code in Erlang, and I get the correct answer on my machine. But when I submit it on SPOJ it gives an NZEC (non zero exit code) error. I have used built-in functions like halt() and init:stop(), and their specification clearly says that they are used to avoid non-zero exit code error. But still I get the same error. How can I solve this problem?
EDIT The code as required by a comment:
-module(factorial).
-export([main/0]).
main() ->
{ok, [No_of_cases]} = io:fread("", "~d"),
loop(No_of_cases).
loop(0) ->
%init:stop();
halt(1);
loop(No_of_cases) ->
{ok, [Number]} = io:fread("", "~d"),
ResultFactorial = find_factorial(Number,1),
io:format("~p~n",[ResultFactorial]),
loop(No_of_cases-1).
find_factorial(0,Product) ->
Product;
find_factorial(Number,Product) ->
find_factorial(Number-1,Product*Number).

I got the answer. The trick is that your module name always has to be tested and the entry point should be function main . For example, after compilation it should be run as tested:main().

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