all recipes 'printed block -> blank' are now hidden

1. bug
There was a bug that the letter machine had "eaten" from the input
slot when there was a different letter type already in the output
slot.

2. stickers
With "default:paper" as input the letter machine makes as now stickers.
They are wallmounted and are destroyed when removed.

init.lua

@@ -22,6 +22,7 @@ local additional_chars = {
 }
 
 local characters = {}
+local characters_sticker = {}
 
 ehlphabet = {}
 ehlphabet.path = minetest.get_modpath(minetest.get_current_modname())
@@ -55,6 +56,9 @@ table_merge(characters, cyrillic_chars)
 table_merge(characters, greek_chars)
 table_merge(characters, additional_chars)
 
+table_merge(characters_sticker, characters)
+table.insert(characters_sticker, " ")
+
 local create_alias = true
 
 -- generate all available blocks
@@ -82,10 +86,10 @@ for _, name in ipairs(characters) do
 	    paramtype2 = "facedir",      -- neu
             on_rotate = screwdriver.rotate_simple ,   -- neu
             is_ground_content = false,   --neu
-            groups = {cracky = 3, not_in_creative_inventory = 1, not_in_crafting_guide = 1}
+            groups = {cracky = 3, not_in_creative_inventory = 1, not_in_crafting_guide = 1, ehlphabet_block = 1}
         }
     )
-    minetest.register_craft({type = "shapeless", output = "ehlphabet:block", recipe = {key}})
+--    minetest.register_craft({type = "shapeless", output = "ehlphabet:block", recipe = {key}})
 
     if create_alias then
         minetest.register_alias("abjphabet:" .. name, key)
@@ -95,8 +99,69 @@ for _, name in ipairs(characters) do
     if name == "Z" then
         create_alias = false
     end
+
+    minetest.register_node(
+        key.."_sticker",
+        {
+            description = desc.."Sticker",
+            tiles = {"ehlphabet_" .. file .. ".png"},
+            paramtype = "light",
+            paramtype2 = "wallmounted", -- "colorwallmounted",      
+            on_rotate = screwdriver.rotate_simple ,   
+            drawtype = "nodebox",
+            is_ground_content = false,   
+            drop = "",  -- new
+  	    node_box = {
+			type = "wallmounted",
+			wall_bottom = {-0.5, -0.5, -0.5, 0.5, -0.49, 0.5},
+			wall_top = {-0.5, 0.49, -0.5, 0.5, 0.5, 0.5},
+			wall_side = {-0.5, -0.5, -0.5, -0.49, 0.5, 0.5},
+                },
+            groups = {attached_node = 1, dig_immediate = 2,  
+                         not_in_creative_inventory = 1, 
+			 not_blocking_trains = 1 },
+        }
+    )
+
+
+
 end
 
+minetest.register_craft({type = "shapeless", output = "ehlphabet:block", recipe = {"group:ehlphabet_block"}})
+
+
+
+-- empty sticker
+
+local key = "ehlphabet:32"
+local file = ("%03d"):format(32)
+local desc = S("Ehlphabet Block '@1'", name)
+
+minetest.register_node(
+ key.."_sticker",
+ {
+    description = desc.."Sticker",
+    tiles = {"ehlphabet_000.png"},
+    paramtype = "light",
+    paramtype2 = "wallmounted", -- "colorwallmounted",      
+    on_rotate = screwdriver.rotate_simple ,   
+    drawtype = "nodebox",
+    is_ground_content = false,   
+    drop = "",  -- new
+    node_box = {
+       type = "wallmounted",
+       wall_bottom = {-0.5, -0.5, -0.5, 0.5, -0.49, 0.5},
+       wall_top = {-0.5, 0.49, -0.5, 0.5, 0.5, 0.5},
+       wall_side = {-0.5, -0.5, -0.5, -0.49, 0.5, 0.5},
+    },
+    groups = {attached_node = 1, dig_immediate = 2,  
+       not_in_creative_inventory = 1, 
+       not_blocking_trains = 1 },
+ }
+)
+
+
+
 minetest.register_node(
     "ehlphabet:machine",
     {
@@ -153,12 +218,26 @@ minetest.register_node(
             local meta = minetest.env:get_meta(pos)
             local inv = meta:get_inventory()
             local inputstack = inv:get_stack("input", 1)
+            local outputstack = inv:get_stack("output", 1)
             local ch = fields.lettername
 
-            if ch ~= nil and inputstack:get_name() == "ehlphabet:block" then
+            if ch ~= nil and ch ~= "" then
+                if  inputstack:get_name() == "ehlphabet:block" 
+                 or inputstack:get_name() == "default:paper" then
+                    local ost = outputstack:get_name()
                     local mb = is_multibyte(ch)
                     local key = mb and (ch:byte(1) .. ch:byte(2)) or ch:byte()
-                for _, v in pairs(characters) do
+                    key = key .. (inputstack:get_name() == "default:paper" and "_sticker" or "")
+                    if ost ~= "" and
+                       ost ~= "ehlphabet:"..key then
+                        --  other type in output slot -> abort
+                        return 
+                    end
+                    local clist = characters
+                    if inputstack:get_name() == "default:paper" then
+		       clist = characters_sticker
+		    end
+                    for _, v in pairs(clist) do
                         if v == ch then
                             local give = {}
                             give[1] = inv:add_item("output", "ehlphabet:" .. key)
@@ -169,6 +248,7 @@ minetest.register_node(
                     end
                 end
             end
+        end
     }
 )
 
@@ -267,6 +347,14 @@ minetest.register_craft({
     }
 })
 
+minetest.register_craft({
+    output = "ehlphabet:231171 7",
+    recipe = {
+        {"ehlphabet:83", "ehlphabet:84", "ehlphabet:65"},
+        {"ehlphabet:84", "ehlphabet:73", "ehlphabet:79"},
+        {"ehlphabet:78", "", ""},
+    }
+})