Multioutput rules work!

first/ackbuilder.lua

@@ -204,10 +204,9 @@ local typeconverters = {
 
 		local o = {}
 		for _, s in ipairs(i) do
-			if (type(s) ~= "string") then
-				error(string.format("member of target list '%s' is not a string", propname))
-			end
-
+			if (type(s) == "table") and s.is then
+				o[#o+1] = s
+			elseif (type(s) == "string") then
 				if s:find("^//") then
 					s = s:gsub("^//", "")
 				elseif s:find("^:") then
@@ -216,6 +215,10 @@ local typeconverters = {
 					s = concatpath(cwd, s)
 				end
 				o[#o+1] = loadtarget(s)
+			else
+				error(string.format("member of target list '%s' is not a string or a target",
+					propname))
+			end
 		end
 		return o
 	end,

first/build.lua

@@ -32,6 +32,25 @@ normalrule {
 	}
 }
 
+normalrule {
+	name = "onetwo",
+	ins = {},
+	outleaves = {"one.txt", "two.txt"},
+	commands = {
+		"echo 1 >> %{outs[1]}",
+		"echo 2 >> %{outs[2]}",
+	}
+}
+
+normalrule {
+	name = "concat",
+	ins = {":onetwo"},
+	outleaves = {"result.txt"},
+	commands = {
+		"cat %{ins} > %{outs}"
+	}
+}
+
 simplerule {
 	name = "sorted",
 	ins = { ":random" },