Function as an argument in Erlang

Question

I'm trying to do something like this:

-module(count).
-export([main/0]).
        
sum(X, Sum) -> X + Sum.

main() ->
    lists:foldl(sum, 0, [1,2,3,4,5]).

but see a warning and code fails:

function sum/2 is unused

How to fix the code?

NB: this is just a sample which illustrates problem, so there is no reason to propose solution which uses fun-expression.

Please post a self-contained and minimal version of your module with which the problem can be reproduced. — jub0bs, Jun 30 '15 at 11:07
possible duplicate of [In Erlang, how do you invoke a function dynamically?](http://stackoverflow.com/questions/1310382/in-erlang-how-do-you-invoke-a-function-dynamically) — legoscia, Jun 30 '15 at 11:09
can you try smth like this `lists:foldl(fun(X, Sum) -> X + Sum end, 0, [1,2,3,4]).` ? because i don't have erlang interpreter at hand right now — Dmitry Zagorulkin, Jun 30 '15 at 11:19
@ZagorulkinDmitry , you can use http://ideone.com/ , though it is not so convenient. — , Jun 30 '15 at 11:26

score 9 · Accepted Answer · edited Jun 20 '20 at 09:12

Erlang has slightly more explicit syntax for that:

-module(count).
-export([main/0]).

sum(X, Sum) -> X + Sum.
main() ->
    lists:foldl(fun sum/2, 0, [1,2,3,4,5]).

1 Answers1