Re: iterator sequences (was: Standard libraries)

[Mark Hamburg <mark@...>]

Okay, how about this:

	function iterate( seq )
		return seq
	end

	function seq( f, state, key )
		local self, apply
		apply = function( ff, ... )
			if ff == 'done' then
				return ...
			end
			if ff then
				f = ff
			end
			return self, state, key
		end
		self = function( s, k, ... )
			if s == state then
				return f( s, k )
			elseif s == iterate then
				return f, s, k
			else
				return apply( s( self, f, k, ... ) )
			end
		end
		return self, state, key
	end

Which then enables us to write things like:

	function collect( seq )
		local r = { }
		for k, v in seq( iterate ) do
			r[ k ] = v
		end
		return 'done', r
	end

This shows that iterate can pay off in other ways besides simply performance. (And if I understand LuaJIT's tracing behavior, the performance win for iterate may not even be relevant since state will be a constant in the loop and hence the tests on state will get optimized away even without the use of iterate.)

This is beginning to feel like it could turn into a very useful library...

Mark