implement a memo method for flow

lapis/flow.lua

@@ -1,7 +1,7 @@
-local type, getmetatable, setmetatable, rawset
+local type, getmetatable, setmetatable, rawset, rawget
 do
   local _obj_0 = _G
-  type, getmetatable, setmetatable, rawset = _obj_0.type, _obj_0.getmetatable, _obj_0.setmetatable, _obj_0.rawset
+  type, getmetatable, setmetatable, rawset, rawget = _obj_0.type, _obj_0.getmetatable, _obj_0.setmetatable, _obj_0.rawset, _obj_0.rawget
 end
 local Flow
 local is_flow
@@ -14,6 +14,27 @@ is_flow = function(cls)
   end
   return is_flow(cls.__parent)
 end
+local MEMO_KEY = setmetatable({ }, {
+  __tostring = function()
+    return "::memo_key::"
+  end
+})
+local memo
+memo = function(fn)
+  return function(self, ...)
+    local cache = rawget(self, MEMO_KEY)
+    if not (cache) then
+      cache = { }
+      rawset(self, MEMO_KEY, cache)
+    end
+    if not (cache[fn]) then
+      cache[fn] = {
+        fn(self, ...)
+      }
+    end
+    return unpack(cache[fn])
+  end
+end
 do
   local _class_0
   local _base_0 = {
@@ -105,5 +126,7 @@ do
 end
 return {
   Flow = Flow,
-  is_flow = is_flow
+  is_flow = is_flow,
+  MEMO_KEY = MEMO_KEY,
+  memo = memo
 }

lapis/flow.moon

@@ -1,5 +1,5 @@
 
-import type, getmetatable, setmetatable, rawset from _G
+import type, getmetatable, setmetatable, rawset, rawget from _G
 
 local Flow
 
@@ -8,7 +8,26 @@ is_flow = (cls) ->
   return true if cls == Flow
   is_flow cls.__parent
 
--- a mediator for encapsulating logic between multiple models and a request
+MEMO_KEY = setmetatable {}, __tostring: -> "::memo_key::"
+
+-- make method cached on the instance so that it's not called multiple times
+-- FIXME: if expose assigns is enabled, don't write memo to exposed request
+memo = (fn) ->
+  (...) =>
+    cache = rawget @, MEMO_KEY
+
+    unless cache
+      cache = {}
+      rawset @, MEMO_KEY, cache
+
+    unless cache[fn]
+      cache[fn] = {fn @, ...}
+
+    unpack cache[fn]
+
+-- A flow is a object that forwards all methods and property access that don't
+-- exist on the flow to the wrapped object. This allows you to encapsulate
+-- functionality within the scope of the Flow class
 class Flow
   expose_assigns: false
 
@@ -68,4 +87,4 @@ class Flow
     setmetatable @, mt
 
 
-{ :Flow, :is_flow }
+{ :Flow, :is_flow, :MEMO_KEY, :memo }