From f4b7eca18f8ddd2b68a3a22a0fa589fd7480004a Mon Sep 17 00:00:00 2001
From: Lars Mueller <appgurulars@gmx.de>
Date: Tue, 18 Jan 2022 18:47:38 +0100
Subject: [PATCH] Add func.memoize

---
 func.lua | 18 ++++++++++++++++--
 test.lua | 10 ++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/func.lua b/func.lua
index 11405a9..2ba0465 100644
--- a/func.lua
+++ b/func.lua
@@ -1,6 +1,6 @@
 -- Localize globals
-local error, coroutine, math, modlib, unpack
-	= error, coroutine, math, modlib, unpack
+local error, coroutine, math, modlib, unpack, select, setmetatable
+	= error, coroutine, math, modlib, unpack, select, setmetatable
 
 -- Set environment
 local _ENV = {}
@@ -35,6 +35,20 @@ function values(...)
 	return function() return unpack(args) end
 end
 
+function memoize(func)
+	return setmetatable({}, {
+		__index = function(self, key)
+			local value = func(key)
+			self[key] = value
+			return value
+		end,
+		__call = function(self, arg)
+			return self[arg]
+		end,
+		__mode = "k"
+	})
+end
+
 -- Equivalent to `for x, y, z in iterator, state, ... do callback(x, y, z) end`
 function iterate(callback, iterator, state, ...)
 	local function loop(...)
diff --git a/test.lua b/test.lua
index a8d445d..1a6369c 100644
--- a/test.lua
+++ b/test.lua
@@ -53,6 +53,16 @@ do
 	end
 	assert(next(tab) == nil)
 	assert(func.aggregate(func.add, 1, 2, 3) == 6)
+	local called = false
+	local function fun(arg)
+		assert(arg == "test")
+		local retval = called
+		called = true
+		return retval
+	end
+	local memo = func.memoize(fun)
+	assert(memo(arg) == false)
+	assert(memo(arg) == false)
 end
 
 -- string