From 5cecab147f53f77dcf70a0f1845772d41cff1597 Mon Sep 17 00:00:00 2001
From: acondolu <andrea.condoluci@unibo.it>
Date: Mon, 28 May 2018 15:14:34 +0200
Subject: [PATCH] Machine implements strong reduction

The machine is very inefficient (uses unwind under lambdas)
---
 ocaml/pure.ml | 68 ++++++++++++++++++++++++++++++++++-----------------
 ocaml/util.ml |  1 +
 2 files changed, 46 insertions(+), 23 deletions(-)

diff --git a/ocaml/pure.ml b/ocaml/pure.ml
index 29288aa..f1cac84 100644
--- a/ocaml/pure.ml
+++ b/ocaml/pure.ml
@@ -21,7 +21,7 @@ let rec print ?(l=[]) =
 let lift m =
  let rec aux l =
   function
-   | V n -> V (if n < l then n else n+m)
+   | V n -> V (if n >= l then n+m else n)
    | A (t1,t2) -> A (aux l t1, aux l t2)
    | L t -> L (aux (l+1) t)
    | B -> B
@@ -29,21 +29,22 @@ let lift m =
   aux 0
 
 (* Reference implementation.
-   Reduction machine used below
+   Reduction machine used below *)
 let subst delift_by_one what with_what =
  let rec aux l =
   function
    | A(t1,t2) -> A(aux l t1, aux l t2)
    | V n ->
-       if n = what + l then
+       if (if what < 0 then n = what else n = what + l) then
         lift l with_what
        else
         V (if delift_by_one && n >= l then n-1 else n)
    | L t -> L (aux (l+1) t)
+   | B -> B
  in
   aux 0
 
-let rec whd =
+(* let rec whd =
  function
   | A(t1, t2) ->
      let t2 = whd t2 in
@@ -82,25 +83,46 @@ let unwind ?(tbl = Hashtbl.create 317) m =
 in
  unwind m
 
-let mwhd m =
- let rec aux =
-  function
-   | (e,A(t1,t2),s) ->
-       let t2' = aux (e,t2,[]) in
-       let (_,t,_) = t2' in
-       if t = B
-        then t2'
-        else aux (e,t1,t2'::s)
-   | (e,L t,x::s) -> aux (x::e,t,s)
-   | (e,V n,s) as m ->
-      (try
-        let e,t,s' = List.nth e n in
-        aux (e,t,s'@s)
-       with Failure _ -> m)
-   | (e, B, _) -> (e, B, [])
-   | (_,L _,[]) as m -> m
- in
-  unwind (aux m)
+
+(* let rec print_machine (e,t,s) =
+ "[" ^ String.concat "," (List.map print_machine e) ^
+     "|" ^ print t ^ "|" ^
+     String.concat "," (List.map print_machine s) ^ "]"
+;; *)
+
+  let mwhd m =
+   let rec aux g =
+    function
+    (* mmm -> print_endline (print_machine mmm); match mmm with *)
+     | (e,A(t1,t2),s) ->
+         let t2' = aux g (e,t2,[]) in
+         let (_,t,_) = t2' in
+         if t = B
+          then t2'
+          else aux g (e,t1,t2'::s)
+     | (e,L t,x::s) -> aux g (x::e,t,s)
+     | (e,V n,s) as m ->
+        (try
+          let e,t,s' = List.nth e n in
+          aux g (e,t,s'@s)
+         with Invalid_argument "List.nth" | Failure _ -> m
+         )
+     | (e, B, _) -> (e, B, [])
+     | (e, L t, []) ->
+      let t = subst true 0 (V g) t in
+      (* print_endline ("." ^ string_of_int g ^ " " ^ print_machine ((e,t,[]))); *)
+      let m' = aux (g-1) (e, t, []) in
+      let t' = unwind m' in
+      (* print_endline ("=" ^ print t');
+      print_endline ("==" ^ print (lift 1 t')); *)
+      let t' = subst false g (V 0) (lift 1 t') in
+      (* print_endline ("===" ^ print t'); *)
+      [], (if t' = B then t' else L t'), []
+
+   in
+    unwind (aux ~-2 m)
+;;
+
 let omega should_explode =
  if should_explode
   then let f t = A(t,t) in f (L (f (V 0)))
diff --git a/ocaml/util.ml b/ocaml/util.ml
index a87b96f..05b9526 100644
--- a/ocaml/util.ml
+++ b/ocaml/util.ml
@@ -113,6 +113,7 @@ let var_of_string s =
 let print_name l n =
  if n = -1
   then "*"
+  else if n < 0 then "c" ^ string_of_int n
   else if n >= List.length l then "x" ^ string_of_int (List.length l - n - 1) else List.nth l n
 
 end
-- 
2.39.2