simplify and fix

sexpr.ml

@@ -682,23 +682,13 @@ module SExprMacroExp = struct
 
   let rec eval (ctx: (string * (SExpr.t * SExpr.t)) list) s =
     let open SExpr in
-    let sli, ctx = match s with
-      Cons(l,r) ->
-        (* Cons(1, Cons(2, Nil)) 
-           l: Cons(1, Nil)
-           r: Cons(Cons(2, Nil), Nil)
-           append r l: Cons(1, Cons(Cons(2, Nil), Nil))
-           *)
-        let l, ctx = eval ctx l in
-        let r, ctx = eval ctx r in
-        begin match append r l with
-          Cons(l, Cons(r, Nil)) -> li1 @@ Cons(l,r)
-        | Nil -> Nil
-        | x   -> raise (FIXME x)
-        end, ctx
-    | s -> li1 s, ctx
+    let s, ctx = if is_list s then
+      aggr_flat_map eval ctx s
+    else
+      s, ctx
     in
-    aggr_flat_map check_expands_while ctx sli
+    let s, ctx = check_expands_while ctx s in
+    s, ctx
   (* expr -> list(new exprs) * bool:changed * ctx *)
   and check_expands ctx s =
     let open SExpr in