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Re: Suggestion: extending for and while loops

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You can generalize this for all iterators, and writing your own range iterator as you described, you can even apply it to the "numeric for". Syntactically, I'd consider a "range" iterator as Python has cleaner, but I do understand the performance concerns (mostly related to builtins being globals, globals being highly flexible, and thus Lua being unable to optimize such a thing to the fast numerical for in most cases). Sometimes I even question for-loops in general; function/callback-based iterators would work just as well, but hey, we're not going purely functional here. A decent compromise must be found. Such syntactical sugar is better implemented at a preprocessor level, or just as Lua. Possible Lua syntax for this:

-- Again iterator-based
for ... in iterator_else(function()
	-- this is your else-body
end, ipairs(table)) do
end
-- Functional, doesn't allow breaking unless you implement it as "return true" or the like;
-- might be more flexible as a different return value could be used for continuing. Comes at a performance penalty.
iterator_else(function(...)
	-- this is your loop body
end, function()
	-- this would be your else-body
end, ipairs(table)) -- iterator has to be at the end due to varargs;
-- if you restrict your iterators, you may move this to the beginning of the parameter list
-- Or yet another one, an iterating func that returns whether the loop body was ran:
if iterator_else(function(...)
	-- loop body
end, ipairs(table)) then
	-- this is your else
end
Even more syntax is possible when you start using debug.setmetatable, overriding operators, but that gets rather hacky.

On 17.03.22 09:06, Benoit Germain wrote:
[ 
stat ::= for Name ‘=’ exp ‘,’ exp [‘,’ exp] do block end
Is it important? Maybe not because Lua could offer a range function to perform numerical loops like so, just like it offers pairs()/next() to iterate over table contents:

for i in range(from,to,step) do
    print(i)
end

However the numerical loop exists. (And yes, I understand that I am the devil's advocate here, as the numerical loop saves function calls, so it is beneficial for performance reasons).

Anyway, no big deal. Either Lua authors think it's worthwhile, or not. The most likely is that they already had that idea on their own and decided against it, for reasons of minimalism: don't do it if it's not needed, just like you said. Time to stop the noise :-).


--
Benoit.

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