add Dummy AST node

5 files changed, 88 insertions, 19 deletions

diff --git a/alv/ast.moon b/alv/ast.moon
index b8c14e6..9f0b819 100644
--- a/alv/ast.moon
+++ b/alv/ast.moon
@@ -31,3 +31,15 @@
   --
   -- @function stringify
   -- @treturn string the exact string this Node was parsed from
+
+import Cell from require 'alv.cell'
+import Constant from require 'alv.result.const'
+import Dummy from require 'alv.dummy'
+import Tag from require 'alv.tag'
+
+{
+  :Cell
+  :Constant
+  :Dummy
+  :Tag
+}
diff --git a/alv/builtins.moon b/alv/builtins.moon
index a015bc6..5fe5e99 100644
--- a/alv/builtins.moon
+++ b/alv/builtins.moon
@@ -11,6 +11,7 @@ import Constant from require 'alv.result'
 import Error from require 'alv.error'
 import RTNode from require 'alv.rtnode'
 import Cell from require 'alv.cell'
+import Dummy from require 'alv.dummy'
 import Scope from require 'alv.scope'
 import Tag from require 'alv.tag'
 import op_invoke from require 'alv.invoke'
@@ -407,7 +408,7 @@ trace = Constant.meta
 
       tag = @tag\clone Tag.parse '-1'
       inner = Cell tag, {
-        Constant.literal T.opdef, traceOp, 'trace'
+        Dummy.literal T.opdef, traceOp
         Constant.str tail[1]\stringify 2
         tail[1]
       }
diff --git a/alv/cell.moon b/alv/cell.moon
index 36d5f43..1b035f4 100644
--- a/alv/cell.moon
+++ b/alv/cell.moon
@@ -17,13 +17,6 @@ class Cell
 --- members
 -- @section members
 
-  new: (@tag=Tag.blank!, @children, @white) =>
-    if not @white
-      @white = [' ' for i=1,#@children]
-      @white[0] = ''
-
-    assert #@white == #@children, "mismatched whitespace length"
-
   --- get the head of the cell.
   --
   -- @treturn AST
@@ -125,6 +118,19 @@ class Cell
 --- static functions
 -- @section static
 
+  --- construct a new Cell.
+  --
+  -- @classmethod
+  -- @tparam[opt] Tag tag
+  -- @tparam {AST,...} children
+  -- @tparam[opt] {string,...} white whitespace strings
+  new: (@tag=Tag.blank!, @children, @white) =>
+    if not @white
+      @white = [' ' for i=1,#@children]
+      @white[0] = ''
+
+    assert #@white == #@children, "mismatched whitespace length"
+
   parse_args = (tag, parts) ->
     if not parts
       parts, tag = tag, nil
diff --git a/alv/dummy.moon b/alv/dummy.moon
new file mode 100644
index 0000000..ec16aa5
--- /dev/null
+++ b/alv/dummy.moon
@@ -0,0 +1,61 @@
+----
+-- Dummy AST Node.
+--
+-- Implements the `AST` interface.
+--
+-- @classmod Dummy
+import RTNode from require 'alv.rtnode'
+import Constant from require 'alv.result.const'
+import Error from require 'alv.error'
+
+class Dummy
+--- members
+-- @section members
+
+  --- the contained node.
+  --
+  -- @tfield RTNode node
+
+--- AST interface
+--
+-- `Dummy` implements the `AST` interface.
+-- @section ast
+
+  --- evaluate this Dummy.
+  --
+  -- returns `node`
+  -- @treturn RTNode `node`
+  eval: => @node
+
+  --- create a clone with its own identity.
+  --
+  -- returns a ref to `node`.
+  --
+  -- @tparam Tag parent
+  -- @treturn Cell
+  clone: => @
+
+  --- stringify this Dummy.
+  --
+  -- throws an error, `Dummy` nodes cannot be stringified.
+  stringify: => error Error, 'implementation', "cannot stringify Dummy"
+
+--- static functions
+-- @section static
+
+  --- construct a new Dummy from a `RTNode`.
+  --
+  -- @classmethod
+  -- @tparam RTNode node
+  new: (@node) =>
+
+  --- construct a new Dummy from a plain value.
+  --
+  -- @tparam Type type
+  -- @tparam any value
+  -- @tparam string raw string
+  @literal: (...) -> @@ RTNode result: Constant ...
+
+{
+  :Dummy
+}
diff --git a/alv/result/const.moon b/alv/result/const.moon
index e4367e7..bace973 100644
--- a/alv/result/const.moon
+++ b/alv/result/const.moon
@@ -67,8 +67,6 @@ class Constant extends Result
   -- @tparam Scope scope the scope to evaluate in
   -- @treturn RTNode the evaluation result
   eval: (scope) =>
-    return RTNode result: @ if @literal
-
     switch @type
       when T.num, T.str
         RTNode result: @
@@ -173,15 +171,6 @@ class Constant extends Result
   -- @treturn Constant
   @bang: -> Constant T.bang, true
 
-  --- create a forced-literal Constant.
-  --
-  -- For internal use in `Builtin`s only.
-  --
-  -- @treturn Constant
-  @literal: (...) ->
-    with Constant ...
-      .literal = true
-
   --- wrap and document a value.
   --
   -- wraps `args.value` using `wrap`, then assigns `meta`.