add memoization first draft/idea

Author: atticus-sullivan

lua/luasnip/extras/expand_conditions.lua

@@ -10,4 +10,36 @@ function M.line_end(line_to_cursor)
 	return #line_to_cursor == #line
 end
 
+local memoization_mt = {
+	__unm  = function(o1)    return function() return not o1()      end end,
+	__add  = function(o1,o2) return function() return o1() or  o2() end end,
+	__mul  = function(o1,o2) return function() return o1() and o2() end end,
+	-- TODO more logic operators
+	__call = function(tab)
+		if not tab.mem or tab.invalidate(tab) then
+			tab.mem = tab.func()
+		end
+		return tab.mem
+	end
+}
+-- low level factory
+-- invalidate(table) -> bool: decides if the memoization should be invalidated,
+-- can store state in table
+-- TODO provide invalidate defaults (buffer, cursor, changes, none)
+function M.memoization_factory(func, invalidate)
+	-- always invalidare by default
+	invalidate = invalidate or function() return true end
+	return setmetatable({func=func, invalidate=invalidate}, memoization_mt)
+end
+
+-- F1 = memoization_factory(function() return true  end)
+-- F2 = memoization_factory(function() return false end)
+-- F3 = F1 + F2
+-- F4 = F1 * -F2
+--
+-- local m = {F1=F1, F2=F2, F3=F3, F4=F4}
+-- for _,name in ipairs{"F1", "F2", "F3", "F4"} do
+-- 	print(name, m[name]())
+-- end
+
 return M