Re: The meaning of 'sugar' [Forked from Re: Why do we have ipairs?]

[Paige DePol <lual@...>]

On Jun 11, 2014, at 10:49 PM, Thiago L. <fakedme@gmail.com> wrote:

> On 12/06/2014 00:18, Paige DePol wrote:
>> On Jun 11, 2014, at 9:24 PM, Thiago L. <fakedme@gmail.com> wrote:
>> 
>>> Make it so this is possible:
>>> 
>>> goto stuff
>>> ::label::
>>> print("yay!")
>>> goto exit
>>> ::stuff::
>>> f = label
>>> goto f
>>> ::exit::
>> With my computed goto/switch case patch[1] that is possible:
>> 
>> goto stuff
>> :|label|:
>> print("yay!")
>> goto exit
>> ::stuff::
>> f = "label"
>> jumpto f
>> ::exit::
>> 
>> As goto labels are only used during compile time I created the :|jumpto|: style label for computed gotos, see my patch documentation for full details.
>> 
>> 
>>> And this:
>>> 
>>> t=setmetatable({label1, label2},{__index = function() return default end})
>>> goto t[x] -- errors if t[x] doesn't evaluate to a label
>>> ::label1::
>>> dostuff()
>>> -- fall thru
>>> ::label2::
>>> domorestuff()
>>> goto exit -- break
>>> ::default::
>>> dodefault()
>>> ::exit::
>> switch x
>>     case label1
>>         dostuff()
>>     case label2
>>         domorestuff()
>>         break
>>     else
>>         dodefault()
>> end
>> 
>> 
>> Or, if you prefer:
>> 
>> jumpto or continue on x
>> goto default
>> :|label1|:
>> dostuff()
>> :|label2|:
>> domorestuff()
>> goto exit
>> ::default::
>> dodefault()
>> ::exit::
>> 
>> Note that no meta-tables or closures were required to implement your example with my patch, you can also probably see why I added sugar for the switch statement, it looks a LOT nicer than the raw computed goto syntax! ;)
>> 
>> ~pmd
>> 
>> [1] https://github.com/FizzyPop/lua-patches/tree/master/joint-patches/jump-table%2Bif-shct%2Bcont-loop
>> 
>> 
> Can your thing handle objects? Something like:
> 
> t[_G] = something
> goto t[_G]

Well, no, since you can't easily represent an object as a constant value. Objects in Lua are essentially tables and since you can't use a table as a jumpto point you can't use "objects" either, sorry! ;)

~pmd