Moss growth ABM: Add inner and outer cobble stairs, simplify code

mods/default/functions.lua

@@ -541,23 +541,26 @@ minetest.register_abm({
 -- Moss growth on cobble near water
 --
 
+local moss_correspondences = {
+	["default:cobble"] = "default:mossycobble",
+	["stairs:slab_cobble"] = "stairs:slab_mossycobble",
+	["stairs:stair_cobble"] = "stairs:stair_mossycobble",
+	["stairs:stair_inner_cobble"] = "stairs:stair_inner_mossycobble",
+	["stairs:stair_outer_cobble"] = "stairs:stair_outer_mossycobble",
+	["walls:cobble"] = "walls:mossycobble",
+}
 minetest.register_abm({
 	label = "Moss growth",
-	nodenames = {"default:cobble", "stairs:slab_cobble", "stairs:stair_cobble", "walls:cobble"},
+	nodenames = {"default:cobble", "stairs:slab_cobble", "stairs:stair_cobble",
+		"stairs:stair_inner_cobble", "stairs:stair_outer_cobble",
+		"walls:cobble"},
 	neighbors = {"group:water"},
 	interval = 16,
 	chance = 200,
 	catch_up = false,
 	action = function(pos, node)
-		if node.name == "default:cobble" then
-			minetest.set_node(pos, {name = "default:mossycobble"})
-		elseif node.name == "stairs:slab_cobble" then
-			minetest.set_node(pos, {name = "stairs:slab_mossycobble", param2 = node.param2})
-		elseif node.name == "stairs:stair_cobble" then
-			minetest.set_node(pos, {name = "stairs:stair_mossycobble", param2 = node.param2})
-		elseif node.name == "walls:cobble" then
-			minetest.set_node(pos, {name = "walls:mossycobble", param2 = node.param2})
-		end
+		node.name = moss_correspondences[node.name]
+		minetest.set_node(pos, node)
 	end
 })