Re: Possible Lua enhancements 2: Piping

[Mark Hamburg <mark@...>]

On Dec 18, 2008, at 3:19 AM, Paul Moore wrote:

> 2008/12/18 Mark Hamburg <mark@grubmah.com>:
> > On the other hand, I think there is clarity to be gained from:
> >
> >       producer() >> filter >> consumer
> >
> > You can read the code left-to-right instead of inside-out and  
> > understand
> > what it does.
>
> An immediate thought - you can do this with a driver function
>
>    pipe(producer(), filter1, filter2, ..., consumer)
>
> which looks to me sufficiently straightforward that I doubt new syntax
> is worth it.

That won't work if the producer can generate multiple values and we  
need to pass those along. One of the key use cases I had been thinking  
about was iterators and iterators are represented by three values.

	for k, v in pairs( t ) >> filter_key_type( "string" ) do
		-- operate only on key value pairs with keys of type string
	end

One could do this with pipe( consumer, filter, filter, ... ) 
( producer() ) probably with the filters in the reverse order, but the  
nesting makes the logic harder to follow. Or in the simple case of the  
loop above:

	for k, v in filter_key_type( "string" )( pairs( t ) ) do
		-- operate only on key value pairs with keys of type string
	end

There's also the potential matter of getting order of evaluation  
"correct" if the filter construction interacts with shared state.

Mark