Recursive definition:

-module(a).
-compile(export_all).
high([X|Xs]) ->
    high(Xs, _Result=X).
high([X|Xs], Result) when X > Result ->
    high(Xs, X);
high([_|Xs], Result) ->
    high(Xs, Result);
high([], Result) ->
    Result.

In the shell:

12> c(a).                 
a.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,a}
13> a:high([3, -11, 2, 11, 4]). 
11

Using a library function:

-module(a).
-compile(export_all).
high(Xs) ->
   lists:max(Xs).

In the shell:

21> c(a).                       
a.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,a}
22> a:high([3, -11, 2, 11, 4]).
11