Re: Explanation needed for setfenv replacement for Lua 5.2

[Lorenzo Donati <lorenzodonatibz@...>]

On 05/05/2011 22.53, E. Toernig wrote:
> | lib.Interpreter( function(_ENV)
> |    AddItem "hello!"
> |    AddItem(AN_UPVALUE)
> |    AddItem "Hope You Enjoy!"
> |
> |    PrintResult()  -->  hello! This is a silly DSL! Hope You Enjoy!
> | end)
>
> > It is still too boilerplate IMO when explaining how to write a DSL
> > snippet to a non-programmer
>
> Just an idea: How about misusing the for statement?
>
> | for _ENV in lib.Interpreter do
> |    AddItem "hello!"
> |    AddItem(AN_UPVALUE)
> |    AddItem "Hope You Enjoy!"
> |
> |    PrintResult()  -->  hello! This is a silly DSL! Hope You Enjoy!
> | end
>
> Still the _ENV but it's readable ;-)

Really smart code! But probably too smart :-D ! As I see it my internal 
parser triggers the "what's being iterated here?" exception! :-D
As the old say goes: "Try not to outsmart the 
language/compiler/interpreter!" ;-)
But you told me that: "for" is being misused! :-)
Nevertheless, very smart! I wonder if there is a less academic use for 
that pattern.

P.S.: (for future reference in the archive) I think now AN_UPVALUE 
inside the "for" body is no more an upvalue, but just a local. From the 
manual (emphasis mine):

*****
Because of the lexical scoping rules, local variables can be freely 
accessed by functions defined inside their scope. A *local variable used 
by an inner function* is called an upvalue, or external local variable, 
*inside the inner function*.
*****

Since the body of the "for" is not a closure, technically AN_UPVALUE is 
not an upvalue there (debug.getupvalue doesn't list it, while 
debug.getlocal does).

> Full code below:

[...]

> Ciao, ET.

Cheers!
--
Lorenzo