Changed the concrete syntax of the new keyword to [$endpos($0)].

Now supported by the table back-end.

src/action.mli

@@ -58,5 +58,5 @@ val has_leftend: t -> bool
 (** Check whether the keyword $start or $end is used in the action. *)
 val has_left: t -> bool
 
-(** Check whether the keyword $beforeend is used in the action. *)
+(** Check whether the keyword $endpos($0) is used in the action. *)
 val has_beforeend: t -> bool

src/codePieces.ml

@@ -48,6 +48,11 @@ let token =
    that binding these variables before executing a semantic action is
    meaningful. *)
 
+(* These names should agree with the printing function [Keyword.posvar]. *)
+
+let beforeendp =
+  "_endpos__0_"
+
 let startp =
   "_startpos"
 

src/codePieces.mli

@@ -37,6 +37,7 @@ val token: string
 
 (* Variables used to hold start and end positions. *)
 
+val beforeendp: string
 val startp: string
 val endp: string
 

src/invariant.ml

@@ -620,7 +620,7 @@ let rewind node : instruction =
    [sym] must keep track of its end position. (Furthermore, if some initial
    state can reduce an epsilon production, then the sentinel cell at the bottom
    of the stack must contain a position. This does not concern us here.)
-   Similarly, if some state whose incoming symbol is [sym] uses [$beforeendpos],
+   Similarly, if some state whose incoming symbol is [sym] uses [$endpos($0)],
    then [sym] must keep track of its end position. *)
 
 open Keyword
@@ -667,10 +667,10 @@ let () =
       | SyntaxError ->
 	  ()
       | Position (Before, _, _) ->
-          (* Doing nothing here is OK because the presence of [$beforepos]
+          (* Doing nothing here is OK because the presence of [$endpos($0)]
              in a semantic action is taken account below when we look at
              every state and check whether it can reduce a production whose
-             semantic action contains [$beforepos]. *)
+             semantic action contains [$endpos($0)]. *)
           ()
       | Position (Left, where, _) ->
 	  require_aux where prod

src/keyword.ml

@@ -57,7 +57,7 @@ let where = function
 
 let subject = function
   | Before ->
-      "before"
+      "__0_"
   | Left ->
       ""
   | RightNamed id ->

src/keyword.mli

@@ -25,7 +25,7 @@ type where =
    and desugared as a [subject] during keywords rewriting into actual
    OCaml identifiers. (See {!Lexer.transform_keywords}.)
 
-   We add a new subject, [Before], which corresponds to [$beforeendpos]
+   We add a new subject, [Before], which corresponds to [$endpos($0)]
    in concrete syntax. We adopt the (slightly awkward) convention that
    when the subject is [Before], the [where] component must be [WhereEnd]. *)
 type parsed_subject =

src/lr1.ml

@@ -844,7 +844,7 @@ let invert reductions : TerminalSet.t ProductionMap.t =
 
 (* This is the case if [s] can reduce an epsilon production whose semantic
    action uses [$startpos] or [$endpos]. This is also the case if [s] can
-   reduce a production whose semantic action uses [$beforeendpos]. *)
+   reduce a production whose semantic action uses [$endpos($0)]. *)
 
 let has_beforeend node =
   TerminalMap.fold (fun _ prods accu ->

src/nonTerminalDefinitionInlining.ml

@@ -26,7 +26,7 @@ let index2id producers i =
    respectively. *)
 
 (* It does not modify [$startpos] or [$endpos], of course, nor [$startpos(y)]
-   and [$endpos(y)] for some other [y]. It does not modify [$beforeendpos]. *)
+   and [$endpos(y)] for some other [y]. It does not modify [$endpos($0)]. *)
 
 let rename_sw_outer (x, startp, endp) (subject, where) : (subject * where) option =
   match subject with
@@ -42,16 +42,16 @@ let rename_sw_outer (x, startp, endp) (subject, where) : (subject * where) optio
         None
 
 (* [rename_sw_inner] transforms the keywords in the inner production (the callee)
-   during inlining. It looks for [$beforepos], [$startpos], and [$endpos,] and
-   replaces them with [beforep], [startp], and [endp], respectively. *)
+   during inlining. It looks for [$endpos($0)], [$startpos], and [$endpos], and
+   replaces them with [beforeendp], [startp], and [endp], respectively. *)
 
 (* It does not modify any [$startpos(x)], of course. *)
 
-let rename_sw_inner (beforep, startp, endp) (subject, where) : (subject * where) option =
+let rename_sw_inner (beforeendp, startp, endp) (subject, where) : (subject * where) option =
   match subject, where with
   | Before, _ ->
       assert (where = WhereEnd);
-      Some beforep
+      Some beforeendp
   | Left, WhereStart ->
       Some startp
   | Left, WhereEnd ->
@@ -191,7 +191,7 @@ let inline grammar =
           else
             (* If the inner production is epsilon and the prefix is empty, then
                we need to look up the end position stored in the top stack cell.
-               This is the reason why we need the keyword [$beforeendpos]. It is
+               This is the reason why we need the keyword [$endpos($0)]. It is
                required in this case to preserve the semantics of $startpos and
                $endpos. *)
             Before, WhereEnd
@@ -215,13 +215,13 @@ let inline grammar =
 
         in
 
-        (* We must also transform [$beforeendpos] if it used by the inner
+        (* We must also transform [$endpos($0)] if it used by the inner
            production. It refers to the end position of the stack cell
            that comes before the inner production. So, if the prefix is
            non-empty, then it translates to the end position of the last
-           element of the prefix. Otherwise, it translates to [$beforeendpos]. *)
+           element of the prefix. Otherwise, it translates to [$endpos($0)]. *)
 
-        let beforep =
+        let beforeendp =
           if prefix > 0 then
             RightNamed (index2id (prefix - 1)), WhereEnd
           else
@@ -232,7 +232,7 @@ let inline grammar =
 	let outer_action =
 	  Action.rename (rename_sw_outer (c, startp, endp)) [] b.action
 	and action' =
-	  Action.rename (rename_sw_inner (beforep, startp, endp)) phi pb.action
+	  Action.rename (rename_sw_inner (beforeendp, startp, endp)) phi pb.action
 	in
 
 	{ b with

src/tableBackend.ml

@@ -205,10 +205,16 @@ let reducebody prod =
     ) (0, PVar stack, []) (Invariant.prodstack prod)
   in
 
-  (* Determine start and end positions for the left-hand side of the
-     production. *)
+  (* Determine beforeend/start/end positions for the left-hand side of the
+     production, and bind them to the conventional variables [beforeendp],
+     [startp], and [endp]. These variables may be unused by the semantic
+     action, in which case these bindings are dead code and can be ignored
+     by the OCaml compiler. *)
 
   let posbindings =
+    ( PVar beforeendp,
+      endpos_of_top_stack_cell
+    ) ::
     ( PVar startp,
       if length > 0 then
 	EVar (Printf.sprintf "_startpos_%s_" ids.(0))