Re: Self-awareness of functions?

[Michal Kolodziejczyk <miko@...>]

On 29.12.2010 08:22, Dirk Laurie wrote:
> 
> In Lua you must take care if you want to define a global recursive 
> function.  Thus:

Why? What problems do you expect?

> 
> do  local fact
>     fact = function(x) if x<2 then return 1 else return x*fact(x-1) end end
>     fac = fact
>     end
> fact = "Napoleon escaped from Elba."
> print(fac(5)) --> 120
> 
> You can't omit any of that padding: create a local variable, then 
> assign it to a global variable, all in an enclosing block.
> 
> Because of the need for a local name for the function, you can't define
> an anonymous recursive function, e.g. for use in an argument list.  
> 
> A standard name like "self" which makes the function aware of itself,
> would be useful:
> 
> function(x) if x<2 then return 1 else return x*self(x-1) end end

So write a self-aware function (much like object:method() syntax sugar):

local myfunction=function(self, x) if x<2 then return 1 else return
x*self(self, x-1) end end

local result=myfunction(myfunction, 5)

Or use callable objects:

Fact=setmetatable({}, {__call=function(self, x) if x<2 then return 1
else return x*self(x-1) end end})

local result=Fact(5)

> Trouble is, I can't see a way to write a C function "self" that 
> can be imported into the global namespace and would achieve this.

I still don't see why you would need such complicated strategy. If your
recursive function is global, then it does not need to be self-aware.
If you need an anonymous self-aware function, just define one and use it
like that (maybe wrapped as a callable oject to simplify the API).

Regards,
miko