diff -r 946c7d13faac -r 814b06660220 scansion/iterators.lua
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/scansion/iterators.lua	Tue Oct 27 19:35:11 2015 +0000
@@ -0,0 +1,201 @@
+-- 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 ]]--
+
+local it = {};
+
+local t_insert = table.insert;
+local select, unpack, next = select, unpack, next;
+local function pack(...) return { n = select("#", ...), ... }; end
+
+-- Reverse an iterator
+function it.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
+		t_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 it.keys(t)
+	return _keys_it, t;
+end
+
+-- Iterate only over values in a table
+function it.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 it.unique(f, s, var)
+	local set = {};
+
+	return function ()
+		while true do
+			local ret = pack(f(s, var));
+			var = ret[1];
+		        if var == nil then break; end
+		        if not set[var] then
+				set[var] = true;
+				return unpack(ret, 1, ret.n);
+			end
+		end
+	end;
+end
+
+--[[ Return the number of items an iterator returns ]]--
+function it.count(f, s, var)
+	local x = 0;
+
+	while true do
+		var = f(s, var);
+	        if var == nil then break; end
+		x = x + 1;
+	end
+
+	return x;
+end
+
+-- Return the first n items an iterator returns
+function it.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 it.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 it.tail(n, f, s, var)
+	local results, count = {}, 0;
+	while true do
+		local ret = pack(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
+		local ret = results[((count-1+pos)%n)+1];
+		return unpack(ret, 1, ret.n);
+	end
+	--return reverse(head(n, reverse(f, s, var))); -- !
+end
+
+function it.filter(filter, f, s, var)
+	if type(filter) ~= "function" then
+		local filter_value = filter;
+		function filter(x) return x ~= filter_value; end
+	end
+	return function (s, var)
+		local ret;
+		repeat ret = pack(f(s, var));
+			var = ret[1];
+		until var == nil or filter(unpack(ret, 1, ret.n));
+		return unpack(ret, 1, ret.n);
+	end, s, var;
+end
+
+local function _ripairs_iter(t, key) if key > 1 then return key-1, t[key-1]; end end
+function it.ripairs(t)
+	return _ripairs_iter, t, #t+1;
+end
+
+local function _range_iter(max, curr) if curr < max then return curr + 1; end end
+function it.range(x, y)
+	if not y then x, y = 1, x; end -- Default to 1..x if y not given
+	return _range_iter, y, x-1;
+end
+
+-- Convert the values returned by an iterator to an array
+function it.to_array(f, s, var)
+	local t, var = {};
+	while true do
+		var = f(s, var);
+	        if var == nil then break; end
+		t_insert(t, var);
+	end
+	return t;
+end
+
+-- Treat the return of an iterator as key,value pairs,
+-- and build a table
+function it.to_table(f, s, var)
+	local t, var2 = {};
+	while true do
+		var, var2 = f(s, var);
+	        if var == nil then break; end
+		t[var] = var2;
+	end
+	return t;
+end
+
+function combinations(iterator, ...)
+	local n_inputs = select("#", ...);
+	local inputs = { ... };
+	local f, s, var = {}, {}, {};
+	for i = 1, n_inputs do
+		f[i], s[i], var[i] = iterator(inputs[i]);
+	end
+
+	local level = 1;
+	return function ()
+		while level > 0 do
+			var[level] = f[level](s[level], var[level]);
+			if level == n_inputs and var[level] ~= nil then
+				return unpack(var, 1, n_inputs);
+			elseif var[level] then
+				level = level + 1;
+				f[level], s[level], var[level] = iterator(inputs[level]);
+			else				
+				level = level - 1;
+			end
+		end
+	end
+end
+
+return it;