diff -r 000000000000 -r d17a1b659852 iterators.lua
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/iterators.lua	Sat Sep 18 18:19:37 2010 +0100
@@ -0,0 +1,144 @@
+-- Prosody IM
+-- Copyright (C) 2008-2010 Matthew Wild
+-- Copyright (C) 2008-2010 Waqas Hussain
+-- 
+-- This project is MIT/X11 licensed. Please see the
+-- COPYING file in the source package for more information.
+--
+
+--[[ Iterators ]]--
+
+-- Reverse an iterator
+function reverse(f, s, var)
+	local results = {};
+
+	-- First call the normal iterator
+	while true do
+		local ret = { f(s, var) };
+		var = ret[1];
+	        if var == nil then break; end
+		table.insert(results, 1, ret);
+	end
+	
+	-- Then return our reverse one
+	local i,max = 0, #results;
+	return function (results)
+			if i<max then
+				i = i + 1;
+				return unpack(results[i]);
+			end
+		end, results;
+end
+
+-- Iterate only over keys in a table
+local function _keys_it(t, key)
+	return (next(t, key));
+end
+function keys(t)
+	return _keys_it, t;
+end
+
+-- Iterate only over values in a table
+function values(t)
+	local key, val;
+	return function (t)
+		key, val = next(t, key);
+		return val;
+	end, t;
+end
+
+-- Given an iterator, iterate only over unique items
+function unique(f, s, var)
+	local set = {};
+	
+	return function ()
+		while true do
+			local ret = { f(s, var) };
+			var = ret[1];
+		        if var == nil then break; end
+		        if not set[var] then
+				set[var] = true;
+				return var;
+			end
+		end
+	end;
+end
+
+--[[ Return the number of items an iterator returns ]]--
+function count(f, s, var)
+	local x = 0;
+	
+	while true do
+		local ret = { f(s, var) };
+		var = ret[1];
+	        if var == nil then break; end
+		x = x + 1;
+	end	
+	
+	return x;
+end
+
+-- Return the first n items an iterator returns
+function head(n, f, s, var)
+	local c = 0;
+	return function (s, var)
+		if c >= n then
+			return nil;
+		end
+		c = c + 1;
+		return f(s, var);
+	end, s;
+end
+
+-- Skip the first n items an iterator returns
+function skip(n, f, s, var)
+	for i=1,n do
+		var = f(s, var);
+	end
+	return f, s, var;
+end
+
+-- Return the last n items an iterator returns
+function tail(n, f, s, var)
+	local results, count = {}, 0;
+	while true do
+		local ret = { f(s, var) };
+		var = ret[1];
+	        if var == nil then break; end
+		results[(count%n)+1] = ret;
+		count = count + 1;
+	end
+
+	if n > count then n = count; end
+
+	local pos = 0;
+	return function ()
+		pos = pos + 1;
+		if pos > n then return nil; end
+		return unpack(results[((count-1+pos)%n)+1]);
+	end
+	--return reverse(head(n, reverse(f, s, var)));
+end
+
+-- Convert the values returned by an iterator to an array
+function it2array(f, s, var)
+	local t, var = {};
+	while true do
+		var = f(s, var);
+	        if var == nil then break; end
+		table.insert(t, var);
+	end
+	return t;
+end
+
+-- Treat the return of an iterator as key,value pairs, 
+-- and build a table
+function it2table(f, s, var)
+	local t, var = {};
+	while true do
+		var, var2 = f(s, var);
+	        if var == nil then break; end
+		t[var] = var2;
+	end
+	return t;
+end