rename Action to Builtin

1 files changed, 96 insertions, 0 deletions

diff --git a/core/base/builtin.moon b/core/base/builtin.moon
new file mode 100644
index 0000000..fd36c69
--- /dev/null
+++ b/core/base/builtin.moon
@@ -0,0 +1,96 @@
+----
+-- Builtin / Special Form evaluation Strategy (`builtin`).
+--
+-- Responsible for quoting/evaluating subexpressions, instantiating and setting
+-- up `Op`s, updating the current `Scope`, etc.
+-- See `builtin` and `invoke` for examples.
+--
+-- @classmod Builtin
+
+class Builtin
+--- Builtin interface.
+--
+-- methods that have to be implemented by `Builtin` implementations.
+-- @section interface
+
+  --- create a new instance.
+  --
+  -- @tparam Cell cell the Cell to evaluate
+  -- @tparam Value head the (`AST:eval`d) `head` of the Cell to evaluate
+  new: (@cell, @head) =>
+    @tag = @cell.tag
+    @tag\register @
+
+  --- perform the actual evaluation.
+  --
+  -- Implementations should:
+  --
+  -- - eval or quote `tail` values
+  -- - perform scope effects
+  -- - wrap all child-results
+  --
+  -- @tparam Scope scope the active scope
+  -- @tparam {AST,...} tail the arguments to this expression
+  -- @treturn Result the result of this evaluation
+  eval: (scope, tail) => error "not implemented"
+
+  --- free resources
+  destroy: =>
+
+  --- setup or copy state from previous instance of same type.
+  --
+  -- `prev` is only passed if Builtin types of prev and current expression match.
+  -- Otherwise, or when no previous expression exists, `nil` is passed.
+  --
+  -- @tparam ?Builtin prev the previous Builtin instance
+  setup: (prev) =>
+
+  --- the `Cell` this Builtin was created for.
+  -- @tfield Cell cell
+
+  --- the evaluated head of `cell`.
+  -- @tfield AST head
+
+  --- the identity of `cell`.
+  -- @tfield Tag tag
+
+--- static functions
+-- @section static
+
+  --- create and setup a `Builtin` for a given tag, then evaluate it.
+  --
+  -- Create a new instance using `tag` and `head` and call `setup` on it.
+  -- If a previous instance with the same `tag` exists and has the same `head`,
+  -- it pass it to `setup`. Register the `Builtin` with `tag`, evaluate it
+  -- and return the `Result`.
+  --
+  -- @tparam Cell cell the `Cell` being evaluated
+  -- @tparam Scope scope the active scope
+  -- @tparam Value head the (`AST:eval`d) head of the `Cell` being evaluated
+  -- @treturn Result the result of evaluation
+  @eval_cell: (cell, scope, head) =>
+    last = cell.tag\last!
+    compatible = last and (last.__class == @) and last.head == head
+
+    L\trace if compatible
+      "reusing #{last} for #{cell.tag} <#{@__name} #{head}>"
+    else if last
+      "replacing #{last} with new #{cell.tag} <#{@__name} #{head}>"
+    else
+      "initializing #{cell.tag} <#{@__name} #{head}>"
+
+    builtin = @ cell, head
+    if compatible
+      builtin\setup last
+    else
+      last\destroy! if last
+      builtin\setup nil
+
+    builtin\eval scope, cell\tail!
+
+  __tostring: => "<#{@@__name} #{@head}>"
+  __inherited: (cls) => cls.__base.__tostring = @__tostring
+
+{
+  :Builtin
+}