Re: switch statement

[David Jeske <jeske@...>]

On Mon, Dec 07, 1998 at 09:35:13PM -0200, David Jeske wrote:
> With a little trickery, you can make this even cooler...
> 
>  Switch{
>    [1] = function (x) B1 end,
>    [2] = function (x) B2 end,
>    ["nop"] = function (x) B3 end,
>    ["my name"] = function (x) B4 end,
>    ["__default__"] = function (x) B5 end
>  }[x](arg);
> 
> Where the 'Switch' function sets the tag of the table so unknown
> accesses return the "__default__" element.

Or you could put the switchvar and arguments up at the top:

Switch(switch_var,{arg1, arg2}, {
    [1] = function (x) B1 end,
    [2] = function (x) B2 end,
    ["nop"] = function (x) B3 end,
    ["my name"] = function (x) B4 end,
    ["__default__"] = function (x) B5 end
});

function Switch(sw_var, args, swtbl)
    local val;

    val = swtbl[sw_var]

    if (not val) then
       val = swtbl["__default__"];
       if (not val) then
            lua_error(format("Missing case in switch ("..
               tostring(sw_var)..")"));
       end
    end

    if (type(val) ~= "function") then
       if (not args) then
          return val; -- passive switch
       else
          lua_error(format("Non function case in switch ("..
              tostring(sw_var)..")"));
       end
    end

    return call(val,args); -- I think this is the right syntax for call()
end

======

I have a question for the Lua implementors though. What are the
performance implications of putting this table initialization syntax
within a function call? What is the overhead of putting the above example in a function vs doing it like this:

switch_tbl = {
    [1] = function (x) B1 end,
    [2] = function (x) B2 end,
    ["nop"] = function (x) B3 end,
    ["my name"] = function (x) B4 end,
    ["__default__"] = function (x) B5 end
};

function a()
   Switch(switch_var,{arg1,arg2},switch_tbl);
end




-- 
David Jeske (N9LCA) + http://www.chat.net/~jeske/ + jeske@chat.net