[GAP Forum] Need Help with first gap code

[sam johnson]

Hey guys I'm new to this forum and i need help with my code. My code should
basically return the position of the maximum element in the list which is
quite easy the problem that it keeps giving me the following message and
I'm sure the logic of the code is correct.

Code:
whereismax := function(L)
    local x, maxpos;
    maxpos := 0;
    for x in [1..Size(L)-1]do
         if  L[x] > L[maxpos] then
            maxpos :=  x;
         fi;
    od;
    return maxpos;
end;


Error message:
Error, no method found! For debugging hints type ?Recovery from
NoMethodFound
Error, no 1st choice method found for `[]' on 2 arguments called from
Size( L ) called from
<function "whereismax">( <arguments> )
 called from read-eval loop at line 40 of *stdin*