Fix binary list operators

`List_append_last v lst` was changed into `List_cons v lst`
which conses `v` to the head of `lst`.

`List_append lst v` was changed into `List_append l0 l1`
which appends l1 to l0.

src/ast/expr.ml

@@ -361,8 +361,12 @@ let rec binop ty (op : binop) (hte1 : t) (hte2 : t) : t =
     let v = value (Eval.binop ty Mul v1 v2) in
     binop' ty Mul v x
   | At, List es, Val (Int n) -> List.nth es n
-  | List_append_last, List es, _ -> make (List (es @ [ hte2 ]))
-  | List_append, List es, _ -> make (List (hte2 :: es))
+  | List_cons, _, List es -> make (List (hte1 :: es))
+  | List_append, List _, (List [] | Val (List [])) -> hte1
+  | List_append, (List [] | Val (List [])), List _ -> hte2
+  | List_append, List l0, Val (List l1) -> make (List (l0 @ List.map value l1))
+  | List_append, Val (List l0), List l1 -> make (List (List.map value l0 @ l1))
+  | List_append, List l0, List l1 -> make (List (l0 @ l1))
   | _ -> binop' ty op hte1 hte2
 
 let triop' (ty : Ty.t) (op : triop) (e1 : t) (e2 : t) (e3 : t) : t =

src/ast/ty.ml

@@ -97,7 +97,7 @@ type binop =
   | Rotl
   | Rotr
   | At
-  | List_append_last
+  | List_cons
   | List_append
   (* String *)
   | String_prefix
@@ -126,15 +126,15 @@ let binop_equal o1 o2 =
   | Rotl, Rotl
   | Rotr, Rotr
   | At, At
-  | List_append_last, List_append_last
+  | List_cons, List_cons
   | List_append, List_append
   | String_prefix, String_prefix
   | String_suffix, String_suffix
   | String_contains, String_contains
   | String_last_index, String_last_index ->
     true
   | ( ( Add | Sub | Mul | Div | DivU | Rem | RemU | Shl | ShrA | ShrL | And | Or
-      | Xor | Pow | Min | Max | Rotl | Rotr | At | List_append_last
+      | Xor | Pow | Min | Max | Rotl | Rotr | At | List_cons
       | List_append | String_prefix | String_suffix | String_contains
       | String_last_index )
     , _ ) ->
@@ -326,7 +326,7 @@ let pp_binop fmt (op : binop) =
   | Rotl -> Fmt.string fmt "rotl"
   | Rotr -> Fmt.string fmt "rotr"
   | At -> Fmt.string fmt "at"
-  | List_append_last -> Fmt.string fmt "append_last"
+  | List_cons-> Fmt.string fmt "cons"
   | List_append -> Fmt.string fmt "append"
   | String_prefix -> Fmt.string fmt "prefixof"
   | String_suffix -> Fmt.string fmt "suffixof"

src/ast/ty.mli

@@ -73,7 +73,7 @@ type binop =
   | Rotl
   | Rotr
   | At
-  | List_append_last
+  | List_cons
   | List_append
   (* String *)
   | String_prefix (* (str.prefixof String String Bool) *)

src/interpret/eval.ml

@@ -401,8 +401,8 @@ module Lst = struct
       let i = Int.of_value 2 op' v2 in
       try List.nth lst i
       with Failure _ | Invalid_argument _ -> raise IndexOutOfBounds )
-    | List_append_last -> List (of_value 1 op' v1 @ [ v2 ])
-    | List_append -> List (v2 :: of_value 2 op' v1)
+    | List_cons -> List (v1 :: of_value 1 op' v2)
+    | List_append -> List (of_value 1 op' v1 @ of_value 2 op' v2)
     | _ -> Fmt.failwith {|binop: Unsupported list operator "%a"|} Ty.pp_binop op
 
   let triop (op : triop) (v1 : Value.t) (v2 : Value.t) (v3 : Value.t) : Value.t

test/unit/test_binop.ml

@@ -60,14 +60,15 @@ let () =
 let () =
   let clist = list [ Int 0; Int 1; Int 2 ] in
   assert (binop Ty_list At clist (int 0) = int 0);
-  assert (binop Ty_list List_append_last (list [ Int 0; Int 1 ]) (int 2) = clist);
-  assert (binop Ty_list List_append (list [ Int 1; Int 2 ]) (int 0) = clist);
+  assert (binop Ty_list List_cons (int 0) (list [ Int 1; Int 2 ]) = clist);
+  assert (
+    binop Ty_list List_append (list [ Int 0; Int 1 ]) (list [ Int 2 ]) = clist );
   let slist2 = make (List [ int 0; int 1 ]) in
   let slist3 = make (List [ int 0; int 1; int 2 ]) in
   assert (binop Ty_list At slist3 (int 0) = int 0);
-  assert (binop Ty_list List_append_last slist2 (int 2) = slist3);
+  assert (binop Ty_list List_append slist2 (list [ Int 2 ]) = slist3);
   assert (
-    binop Ty_list List_append (make (List [ int 1; int 2 ])) (int 0) = slist3 )
+    binop Ty_list List_cons (int 0) (make (List [ int 1; int 2 ])) = slist3 )
 
 (* i32 *)
 let () =