Re: Coroutines & Iterators
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- Subject: Re: Coroutines & Iterators
- From: MichaelL@...
- Date: 2003年1月13日 11:46:22 -0500
> With the introduction of coroutines to Lua, the section of the manual
> dealing with the "for" statement needs to be cleaned up.
Well, obviously I agree. :-)
But given the distraction my main point was ignored: with a little
syntactic sugar, Lua's first-class anonymous functions would be more
"usable."
I've modified my copy of Lua 5 with the following:
* "iterator x( a, b ) ..." is exactly syntactic sugar for "function ( a,
b, yield ) ...".
* "begin ( v ) ..." is exactly syntactic sugar for "function ( v ) ...".
* a "begin ..." following a function call is automatically added as a
parameter to the preceding call.
With those changes I can now do things like this:
Table{ "a", "b", "c" }:filter() begin ( v )
if v >= "b" then return true end
end
io.withOutputTo ( "somefile.txt" ) begin ()
io.write( "some text" )
io.write( "some more text" )
io.write( "some text" )
end
with implementations like this:
iterator table.filter( t )
local result = {}
table.foreach( t ) begin (i, v)
if yield( v ) then
table.insert( t, v )
end
end
return result
end
iterator io.withOutputTo( f )
io.output( f )
yield()
io.output()
end
The changes I made work independently. For example, if you look at the
"filter" implementation you'll see that it uses the existing
"table.foreach" function--even though it wasn't defined as an "iterator."
My changes simply add the "begin" block as an anonymous function to the
preceding function call. As I said before, it's just syntactic sugar for
things that Lua can already do.
I'll be making a few more changes to make things a bit prettier. For
example, I want parentheses to be optional when there are no arguments. And
I want to find something better than "begin" to mark the block following a
function call...