Re: Microlight
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- Subject: Re: Microlight
- From: Jay Carlson <nop@...>
- Date: 2012年12月20日 17:12:55 -0500
On Dec 20, 2012, at 11:02 AM, Philipp Janda wrote:
> And collect/icollect ([1], slightly altered) are actually surprisingly interesting:
>
> icollect( {}, 1, pairs( t ) ) --> keys( t )
> icollect( {}, 2, pairs( t ) ) --> values( t )
> icollect( {}, 2, ipairs( t ) ) --> shallow_arraycopy( t )
> icollect( {}, 1, io.lines( fname ) ) --> my @lines = <FILE>;
> icollect( t1, 2, ipairs( t2 ) ) --> append( t1, t2 )
>
> collect( {}, 1, 2, pairs( t ) ) --> shallow_tablecopy( t )
> collect( {}, 1, 2, ipairs( t ) ) --> shallow_arraycopy( t )
> collect( {}, 2, 1, ipairs( t ) ) --> invert( t ), makeset( t )
> collect( t1, 1, 2, pairs( t2 ) ) --> extend( t1, t2 )
I really like this, but I hate numbers. Consider a function swap():
swap(1, 2)
-> return 2, 1
swap(1, 2, 3)
-> return 2, 1, 3
swap(1, nil)
-> return nil, 1
-- I'm ultra-paranoid. Would you ever want this to work?
swap(1)
-> error()
I thought it was a shame you can't write a no-memory iterator that applies swap() to another iterator's stepping. (You can't because the "next step" function is only called with *first* value it previously returned.) It'd look like a function swap()ing its arguments and its return values.
Perhaps a wrapper calling "swap" per step could be called swaps()--it fits with pairs() and ipairs().
That way those examples could become
icollect({}, pairs( t ) ) -> keys(t)
icollect({}, swaps( pairs( t ) )) -> values(t)
collect({}, swaps( ipairs( t ) )) -> invert/Set(t)
As a technical matter it would be easy to change the generic-for implementation to pass in two values, and of course we can do whatever we want with collect and icollect.
But after having gone through all that, icollect_2nd() and collect_2nd() would be even easier. swaps() seems like it has very limited utility in the generic-for.
icollect_n and collect_n are a really nice general case.
...but after all that theory I'm reluctantly walking back to "but would I actually use that with that name". I could write something like table.values(t) but probably just admire icollect_2nd({}, pairs(t)) from afar.
inject_into({}, t) and invert_into({}, t) (whatever their names) are the big ones for me.