diff --git a/build.lua b/build.lua
index 7b28b0d30..cc483e438 100644
--- a/build.lua
+++ b/build.lua
@@ -1,3 +1,7 @@
+vars.cflags = {
+	"-g", "-O"
+}
+
 installable {
 	name = "ack",
 	map = {
diff --git a/first/ackbuilder.lua b/first/ackbuilder.lua
index fa56a8474..05772af2e 100644
--- a/first/ackbuilder.lua
+++ b/first/ackbuilder.lua
@@ -15,6 +15,18 @@ local targets = {}
 local buildfiles = {}
 local globals
 local cwd = "."
+local vars = {}
+local parente = {}
+
+local function concat(...)
+	local r = {}
+	for k, t in ipairs({...}) do
+		for _, v in ipairs(t) do
+			r[#r+1] = v
+		end
+	end
+	return r
+end
 
 local function inherit(high, low)
 	local o = {}
@@ -27,6 +39,12 @@ local function inherit(high, low)
 			return low[k]
 		end
 	})
+	for k, v in pairs(high) do
+		local _, _, kk = k:find("^%+(.*)$")
+		if kk then
+			o[kk] = concat(low[kk], v)
+		end
+	end
 	return o
 end
 
@@ -53,16 +71,6 @@ local function asstring(o)
 	end
 end
 
-local function concat(...)
-	local r = {}
-	for _, t in ipairs({...}) do
-		for _, v in ipairs(t) do
-			r[#r+1] = v
-		end
-	end
-	return r
-end
-
 local function concatpath(...)
 	local p = table.concat({...}, "/")
 	return (p:gsub("/+", "/"):gsub("^%./", ""):gsub("/%./", "/"))
@@ -404,6 +412,7 @@ local function definerule(rulename, types, cb)
 
 	types.name = { type="string" }
 	types.cwd = { type="string", optional=true }
+	types.vars = { type="table", default={} }
 
 	for propname, typespec in pairs(types) do
 		if not typeconverters[typespec.type] then
@@ -414,6 +423,11 @@ local function definerule(rulename, types, cb)
 
 	local rulecwd = cwd
 	local rule = function(e)
+		local definedprops = {}
+		for propname, _ in pairs(e) do
+			definedprops[propname] = true
+		end
+
 		local args = {}
 		for propname, typespec in pairs(types) do
 			if not e[propname] then
@@ -424,11 +438,11 @@ local function definerule(rulename, types, cb)
 				args[propname] = typespec.default
 			else
 				args[propname] = typeconverters[typespec.type](propname, e[propname])
-				e[propname] = nil
+				definedprops[propname] = nil
 			end
 		end
 
-		local propname, _ = next(e)
+		local propname, _ = next(definedprops)
 		if propname then
 			error(string.format("don't know what to do with property '%s'", propname))
 		end
@@ -438,7 +452,11 @@ local function definerule(rulename, types, cb)
 		end
 		args.fullname = args.cwd.."+"..args.name
 
+		local oldparente = parente
+		parente = args
+		args.vars = inherit(args.vars, oldparente.vars)
 		local result = cb(args) or {}
+		parente = oldparente
 
 		result.is = result.is or {}
 		result.is[rulename] = true
@@ -678,6 +696,7 @@ globals = {
 	startswith = startswith,
 	targetnamesof = targetnamesof,
 	uniquify = uniquify,
+	vars = vars,
 }
 setmetatable(globals,
 	{
@@ -692,6 +711,9 @@ setmetatable(globals,
 	}
 )
 
+vars.cflags = {}
+parente.vars = vars
+
 do
 	local emitter_type = install_make_emitter
 	parse_arguments(
diff --git a/first/build.lua b/first/build.lua
index 31c790f13..e514384b9 100644
--- a/first/build.lua
+++ b/first/build.lua
@@ -10,7 +10,6 @@ definerule("normalrule",
 		label = { type="string", optional=true },
 		objdir = { type="string", optional=true },
 		commands = { type="strings" },
-		vars = { type="table", default={} },
 	},
 	function (e)
 		local dir = e.objdir or objdir(e)
@@ -41,7 +40,6 @@ definerule("cfile",
 	{
 		srcs = { type="targets" },
 		deps = { type="targets", default={} },
-		cflags = { type="strings", default={} },
 		commands = {
 			type="strings",
 			default={
@@ -74,7 +72,6 @@ definerule("cfile",
 			commands = e.commands,
 			vars = {
 				hdrpaths = hdrpaths,
-				cflags = e.cflags,
 			}
 		}
 	end
@@ -85,7 +82,6 @@ definerule("cppfile",
 		srcs = { type="targets" },
 		deps = { type="targets", default={} },
 		outleaf = { type="string" },
-		cflags = { type="strings", default={} },
 		commands = {
 			type="strings",
 			default={
@@ -114,7 +110,6 @@ definerule("cppfile",
 			commands = e.commands,
 			vars = {
 				hdrpaths = hdrpaths,
-				cflags = e.cflags,
 			}
 		}
 	end
@@ -155,7 +150,6 @@ definerule("clibrary",
 		srcs = { type="targets", default={} },
 		hdrs = { type="targets", default={} },
 		deps = { type="targets", default={} },
-		cflags = { type="strings", default={} },
 		commands = {
 			type="strings",
 			default={
@@ -176,9 +170,8 @@ definerule("clibrary",
 				cwd = e.cwd,
 				srcs = {csrc, unpack(hsrcs)},
 				deps = e.deps,
-				cflags = {
-					"-I"..e.cwd,
-					unpack(e.cflags)
+				vars = {
+					["+cflags"] = { "-I"..e.cwd, },
 				},
 			}
 		end
@@ -212,7 +205,6 @@ definerule("cprogram",
 	{
 		srcs = { type="targets", default={} },
 		deps = { type="targets", default={} },
-		cflags = { type="strings", default={} },
 		commands = {
 			type="strings",
 			default={
@@ -230,7 +222,6 @@ definerule("cprogram",
 						cwd = e.cwd,
 						srcs = e.srcs,
 						deps = e.deps,
-						cflags = e.cflags,
 					}
 				},
 				"%.a$"
diff --git a/modules/src/em_code/build.lua b/modules/src/em_code/build.lua
index 80ea28a8b..b530f2a51 100644
--- a/modules/src/em_code/build.lua
+++ b/modules/src/em_code/build.lua
@@ -79,10 +79,12 @@ local function build_variant(code, cflags)
 			"modules/src/system+lib",
 			"util/data+em_data",
 		},
-		cflags = { cflags }
+		vars = {
+			["+cflags"] = cflags
+		},
 	}
 end
 
-build_variant("e", "-DREADABLE_EM")
-build_variant("k", "")
+build_variant("e", { "-DREADABLE_EM" })
+build_variant("k", { })
 
diff --git a/modules/src/read_em/build.lua b/modules/src/read_em/build.lua
index 860f29df1..d80d0569c 100644
--- a/modules/src/read_em/build.lua
+++ b/modules/src/read_em/build.lua
@@ -27,11 +27,13 @@ normalrule {
 	
 clibrary {
 	name = "lib_ev",
-	cflags = {
-		"-DPRIVATE=static",
-		"-DEXPORT=",
-		"-DNDEBUG",
-		"-DCHECKING"
+	vars = {
+		["+cflags"] = {
+			"-DPRIVATE=static",
+			"-DEXPORT=",
+			"-DNDEBUG",
+			"-DCHECKING"
+		},
 	},
 	srcs = {
 		"./EM_vars.c",
diff --git a/util/LLgen/build.lua b/util/LLgen/build.lua
index fd60daa59..5939332d4 100644
--- a/util/LLgen/build.lua
+++ b/util/LLgen/build.lua
@@ -6,7 +6,12 @@ cprogram {
 	-- do this.
 
 	srcs = { "./src/*.c" },
-	cflags = { "-DLIBDIR=\\\""..posix.getcwd().."/"..cwd().."/lib\\\"", "-DNON_CORRECTING" },
+	vars = {
+		["+cflags"] = {
+			"-DLIBDIR=\\\""..posix.getcwd().."/"..cwd().."/lib\\\"",
+			"-DNON_CORRECTING"
+		},
+	}
 }
 
 definerule("llgen",