When to prefer `and` over `andalso` in guard tests

Question

I am curious why the comma ‹,› is a shortcut for and and not andalso in guard tests.

Since I\'d call myself a “C native” I fail to see any shor

Answer 1

Adam Lindbergs link is right. Using the comma does generate better beam code than using andalso. I compiled the following code using the +to_asm flag:

a(A,B) ->
    case ok of
        _ when A, B -> true;
        _ -> false
    end.
aa(A,B) ->
    case ok of
        _ when A andalso B -> true;
        _ -> false
    end.

which generates

{function, a, 2, 2}.
  {label,1}.
    {func_info,{atom,andAndAndalso},{atom,a},2}.
  {label,2}.
    {test,is_eq_exact,{f,3},[{x,0},{atom,true}]}.
    {test,is_eq_exact,{f,3},[{x,1},{atom,true}]}.
    {move,{atom,true},{x,0}}.
    return.
  {label,3}.
    {move,{atom,false},{x,0}}.
    return.

{function, aa, 2, 5}.
  {label,4}.
    {func_info,{atom,andAndAndalso},{atom,aa},2}.
  {label,5}.
    {test,is_atom,{f,7},[{x,0}]}.
    {select_val,{x,0},{f,7},{list,[{atom,true},{f,6},{atom,false},{f,9}]}}.
  {label,6}.
    {move,{x,1},{x,2}}.
    {jump,{f,8}}.
  {label,7}.
    {move,{x,0},{x,2}}.
  {label,8}.
    {test,is_eq_exact,{f,9},[{x,2},{atom,true}]}.
    {move,{atom,true},{x,0}}.
    return.
  {label,9}.
    {move,{atom,false},{x,0}}.
    return.

I only looked into what is generated with the +to_core flag, but obviously there is a optimization step between to_core and to_asm.