The_End/mods/items/repairing_anvils/api.lua

local recipes = {}
repairing_anvils.recipes = recipes

function repairing_anvils.register_recipe(input, output)
	assert(type(input) == "string",
		"Error registering anvil recipe: Input must be a string, was " ..
		type(input))
	assert(type(output) == "string" or
		type(output) == "function",
		"Error registering anvil recipe: output must be a string of function, was" ..
		type(output))
	assert(not recipes[input], "There is already an anvil recipe registered for " ..
		input)



	recipes[minetest.registered_aliases[input] or input] =
		minetest.registered_aliases[output] or output
end