fork ops before eval cycle

3 files changed, 24 insertions, 1 deletions

diff --git a/core/base/op.moon b/core/base/op.moon
index f338673..08c47ab 100644
--- a/core/base/op.moon
+++ b/core/base/op.moon
@@ -19,6 +19,17 @@ class Op
   -- @treturn iterator iterator over `inputs`
   all_inputs: => coroutine.wrap -> do_yield @inputs
 
+  --- create a mutable copy of this Op.
+  --
+  -- Used to wrap insulate eval-cycles from each other. The copy does not have
+  -- `inputs` set, since it is expected that this is (re)set in `setup`.
+  --
+  -- @treturn Value
+  fork: =>
+    with setmetatable {}, getmetatable @
+      .state = {k,v for k,v in pairs @state} if @state
+      .out = @out\fork! if @out
+
   --- `Value` instance representing this Op's computed output value.
   --
   -- Must be set to a `Value` instance once `setup` finishes. Must not change
@@ -92,6 +103,7 @@ class Op
   -- @tparam[opt] string type the type-name for `out`
   -- @tparam[optchain] any init the initial value for `out`
   new: (type, init) =>
+    @state = {}
     if type
       @out = Value type, init
 
diff --git a/core/invoke.moon b/core/invoke.moon
index 8d63962..23207b7 100644
--- a/core/invoke.moon
+++ b/core/invoke.moon
@@ -13,7 +13,9 @@ import Scope from require 'core.scope'
 class op_invoke extends Action
   --- `Action:patch` implementation.
   patch: (head) =>
-    return true if head == @head
+    if head == @head
+      @op = @op\fork!
+      return true
 
     @op\destroy! if @op
 
diff --git a/core/value.moon b/core/value.moon
index 0f40ef3..bda6127 100644
--- a/core/value.moon
+++ b/core/value.moon
@@ -36,6 +36,15 @@ class Value
     assert type == @type, msg or "#{@} is not a #{type}" if type
     @value
 
+  --- create a mutable copy of this Value.
+  --
+  -- Used to wrap insulate eval-cycles from each other.
+  --
+  -- @treturn Value
+  fork: =>
+    with Value @type, @value, @raw
+      .updated = @updated
+
   --- alias for `unwrap`.
   __call: (...) => @unwrap ...