Re: new thought experiment: what would you add to Lua ?

[Lorenzo Donati <lorenzodonatibz@...>]

On 15/09/2018 01:00, Andrew Gierth wrote:
> Ternary (conditional) operator. Using (x and y or z) has become an
> idiom, which shows the real demand for such a feature, but the fact that
> it breaks when y is false or nil makes for a lot of landmines.

I don't find it so problematic, but I agree that newbies could trip on that.

Adding that specific feature could be against the minimalistic nature of 
Lua (too much restricted a use case). But maybe a more general 
expression-like construct could be generally useful (dumb syntax below, 
warning! Just to get the point):

x = if (value) then exp1, exp2, ... expN; (I know it is not valid syntax)

or maybe:

x = ? value : exp1, exp2, ... expN  (shorter but probably more confused)

It's semantically like "select", but not a function call, so amenable to 
more optimization. And moreover is more explicit.

> Something like #... to return the number of varargs without needing to
> pass them all to another function as in select('#',...).

Yep!!! This was a pet peeve of mine for ages.

I generally hate `select` (but I love its functionalities). And I love 
varargs: if used with a grain of salt they make the code flexible and 
still readable.

Maybe #@ to indicate the number of varargs and @[i] the i-th vararg ("@" 
can be read as an "A"/"at", so it makes sense).

Unfortunately, I think I remember Roberto "hates" varargs and he wanted 
to get rid of them. So this "select as operator" has few chances to see 
the light (I'm still hoping he changes his mind, maybe if people on the 
list come up with a nice syntax with general application - maybe with 
expanded semantics... :-)


Maybe the two features before could be merged: make "@" a "select" 
operator, then:

x = @[i](exp1, exp2, ...., expN) is the i-th expression in the list

x = @[condition](false_expr, true_expr) is like a ternary operator 
(unintuitive the order of the results, though)

This could allow use of varargs like this:

x = @[i](...)

n = @#(...)	number of elements in the list


But all this starts to seem like t-uples are added to the language, but 
Roberto don't like this either (IIRC).

Maybe everything could be simplified if Lua provided a way to "declare" 
fixed-length array tables, so that:

{...}

could be optimized and "#" could be made return exactly the number of 
elements ("holes" included) and normal table access with "[i]" would do 
the rest. But now I'm just rambling. :-)


Cheers!

--Lorenzo