пример рекурсии

-export([ld/1]).
ld([])->0;
ld([2|T])->1+ld(T);
ld([_|T])->0+ld(T).
х
ld(E)->ld(E,0).
ld([],Len)->Len;
ld([_|E],Len)->ld(E,Len+1).

get_users()->
[
{user,1,"a",10},
{user,2,"b",150},
{user,3,"c",160},
{user,4,"d",107}
].

get_sum(E)->get_sum(E,0).
get_sum([],N)->N;
get_sum([E|I],N)->
{user,X,_,_}=E,
get_sum(I,N+X).

filter(E)->filter(E,[]).
filter([],Ac)->Ac;
filter([E|I],Ac)->
 case E of
 {user,_,"bob",_}-> filter(I,[E|Ac]) ;
 _-> filter(I,Ac)
end.