Added lume.memoize(), updated README.md and tests

README.md

@@ -208,6 +208,14 @@ f() -- Prints "Hello"
 f() -- Does nothing
 ```
 
+### lume.memoize(fn)
+Returns a wrapper function to `fn` where the results for any given set of
+arguments are cached. `lume.memoize()` is useful when used on functions with
+slow-running computations.
+```lua
+fib = lume.memoize(function(n) return n < 2 and n or fib(n-1) + fib(n-2) end)
+```
+
 ### lume.time(fn, ...)
 Inserts the arguments into function `fn` and calls it. Returns the time in
 seconds the function `fn` took to execute followed by `fn`'s returned values.

lume.lua

@@ -269,6 +269,24 @@ function lume.once(fn, ...)
 end
 
 
+local memoize_fnkey = {}
+local memoize_nilkey = {}
+
+function lume.memoize(fn)
+  local cache = {}
+  return function(...)
+    local c = cache
+    for i = 1, select("#", ...) do
+      local a = select(i, ...) or memoize_nilkey
+      c[a] = c[a] or {}
+      c = c[a]
+    end
+    c[memoize_fnkey] = c[memoize_fnkey] or {fn(...)}
+    return unpack(c[memoize_fnkey])
+  end
+end
+
+
 function lume.time(fn, ...)
   local start = os.clock()
   local rtn = {fn(...)}

test/test_lume.lua

@@ -279,6 +279,20 @@ tests["lume.once"] = function()
   tester.test.error( lume.once, 123 )
 end
 
+-- lume.memoize
+tests["lume.memoize"] = function()
+  local f = lume.memoize(
+    function(a, b, c)
+      return tostring(a) .. tostring(b) .. tostring(c)
+    end)
+  testeq( f("hello", nil, 15),  "hellonil15"  )
+  testeq( f("hello", nil, 15),  "hellonil15"  )
+  testeq( f(),                  "nilnilnil"   )
+  testeq( f(),                  "nilnilnil"   )
+  local f2 = lume.memoize(function() end)
+  testeq( f2(), nil )
+end
+
 -- lume.time
 tests["lume.time"] = function()
   local t, a, b, c = lume.time(function(x) return 50, 60, x end, 70)