newton 21> maple
    |\^/|     Maple V Release 3 (University of Texas - Austin)
._|\|   |/|_. Copyright (c) 1981-1994 by Waterloo Maple Software and the
 \  MAPLE  /  University of Waterloo. All rights reserved. Maple and Maple V
 <____ ____>  are registered trademarks of Waterloo Maple Software.
      |       Type ? for help.
> read example;

                                          23
                                   aa := ---
                                         155


myadd := proc(x:numeric,y:numeric) x+y end


> myadd(3,4);

                                       7

> myadd(a,b);
Error, myadd expects its 1st argument, x, to be of type numeric, 
but received a

> #------------------------------------------------------------

> read ladd;

> op(ladd);

proc(l:list(numeric))
local lsum,i;
    if nops(l) = 0 then ERROR(`argument is the NULL list`) fi;
    lsum := l[1];
    for i from 2 to nops(l) do  lsum := lsum+l[i] od;
    lsum
end

> ladd( [1,2,3,4] );

                                       10

> ladd( [a,b,c] );
Error, ladd expects its 1st argument, l, to be of type list(numeric), 
but received [a, b, c]

> ladd([]);
Error, (in ladd) argument is the NULL list

> ladd([1]);

                                       1

> ladd(1);
Error, ladd expects its 1st argument, l, to be of type list(numeric), 
but received 1

> quit
bytes used=136888, alloc=131048, time=0.04