wip

src/Halogen/VDom/DOM/Types.purs

@@ -43,8 +43,8 @@ type VDomHydrator4 i j k l a w
 -- | Widget machines recursively reference the configured spec to potentially
 -- | enable recursive trees of Widgets.
 newtype VDomSpec a w = VDomSpec
-  { buildWidget ∷ VDomSpec a w → Machine w DOM.Node -- `buildWidget` takes a circular reference to the `VDomSpec`
-  , hydrateWidget ∷ VDomSpec a w → DOM.Element → Machine w DOM.Node
+  { buildWidget ∷ Machine w DOM.Node -- `buildWidget` takes a circular reference to the `VDomSpec`
+  , hydrateWidget ∷ DOM.Element → Machine w DOM.Node
 
   , buildAttributes ∷ DOM.Element → Machine a Unit
   , hydrateAttributes ∷ DOM.Element → Machine a Unit

src/Halogen/VDom/DOM/Widget.purs

@@ -15,7 +15,7 @@ type WidgetState a w =
 
 hydrateWidget ∷ ∀ a w. VDomHydrator w a w
 hydrateWidget = EFn.mkEffectFn5 \elem (VDomSpec spec) _hydrate build w → do
-  res ← EFn.runEffectFn1 (spec.hydrateWidget (VDomSpec spec) elem) w
+  res ← EFn.runEffectFn1 (spec.hydrateWidget elem) w
   let
     res' :: Step (VDom a w) DOM.Node
     res' = res # unStep \(Step n s k1 k2) →
@@ -24,7 +24,7 @@ hydrateWidget = EFn.mkEffectFn5 \elem (VDomSpec spec) _hydrate build w → do
 
 buildWidget ∷ ∀ a w. VDomBuilder w a w
 buildWidget = EFn.mkEffectFn3 \(VDomSpec spec) build w → do
-  res ← EFn.runEffectFn1 (spec.buildWidget (VDomSpec spec)) w
+  res ← EFn.runEffectFn1 spec.buildWidget w
   let
     res' :: Step (VDom a w) DOM.Node
     res' = res # unStep \(Step n s k1 k2) →

test/TestVdom.js

@@ -0,0 +1,34 @@
+/* global exports, require */
+"use strict";
+
+// module Control.Monad.Fix
+
+var message = "Control.Monad.Fix: Premature access to result of fixpoint computation."
+
+function f(x) {
+  console.log(x)
+  return 1
+}
+
+var myobj = { a: f(myobj), b: 2 }
+
+// fixEffect :: forall eff a. ((Unit -> a) -> Eff eff a) -> Eff eff a
+exports.fixEffect = function(f) {
+  return function() {
+    var result = null;
+    var ready = false;
+
+    result = f(function(u) {
+      if (!ready) throw new Error(message);
+      return result;
+    })();
+
+    ready = true;
+    return result;
+  }
+}
+
+// fixPure :: forall a. ((Unit -> a) -> a) -> a
+exports.fixPure = function(f) {
+  return exports.fixEffect(function(a) { return function () { return f(a); }})();
+}

test/TestVdom.purs

@@ -15,6 +15,8 @@ import Web.DOM.Document (Document) as DOM
 import Web.DOM.Element (Element) as DOM
 import Halogen.VDom.Machine (Machine)
 import Effect (Effect)
+import Control.Lazy as CL
+import Data.Lazy as DL
 
 infixr 1 prop as :=
 
@@ -43,13 +45,23 @@ thunk render val = VDom $ V.Widget $ Fn.runFn2 thunk1 render val
 myfn :: ((Void → Effect Unit) -> DOM.Element -> Machine (Array (Prop Void)) Unit) → DOM.Element → Machine (Array (Prop Void)) Unit
 myfn buildProp element = buildProp (const (pure unit)) element
 
+type As a = a -> a
+
+foreign import fixPure :: forall a. ((Unit -> a) -> a) -> a
+
 mkSpec
   ∷ DOM.Document
   → V.VDomSpec (Array (Prop Void)) (Thunk VDom Void)
-mkSpec document = V.VDomSpec
-  { buildWidget: buildThunk (un VDom)
-  , hydrateWidget: hydrateThunk (un VDom)
-  , buildAttributes: buildProp (const (pure unit))
-  , hydrateAttributes: hydrateProp (const (pure unit))
-  , document
-  }
+mkSpec document = DL.force (CL.fix go)
+  where
+    go :: As (DL.Lazy (V.VDomSpec (Array (Prop Void)) (Thunk VDom Void)))
+    go lazySpec =
+      let self = DL.force lazySpec
+       in DL.defer \_ ->
+         V.VDomSpec
+           { buildWidget: buildThunk (un VDom) self
+           , hydrateWidget: hydrateThunk (un VDom) self
+           , buildAttributes: buildProp (const (pure unit))
+           , hydrateAttributes: hydrateProp (const (pure unit))
+           , document
+           }