Fix broken assert()

init.lua

@@ -124,6 +124,14 @@ local function is_str(x)
 	return type(x) == "string"
 end
 
+local function is_num(x)
+	return type(x) == "number"
+end
+
+local function is_table(x)
+	return type(x) == "table"
+end
+
 local function is_func(x)
 	return type(x) == "function"
 end
@@ -142,9 +150,9 @@ end
 function craftguide.register_craft(def)
 	local func = "craftguide." .. __func() .. "(): "
 	assert(is_str(def.type), func .. "'type' field missing")
-	assert(is_str(def.width), func .. "'width' field missing")
+	assert(is_num(def.width), func .. "'width' field missing")
 	assert(is_str(def.output), func .. "'output' field missing")
-	assert(is_str(def.items), func .. "'items' field missing")
+	assert(is_table(def.items), func .. "'items' field missing")
 
 	custom_crafts[#custom_crafts + 1] = def
 end