Add some helpers to String_with_loc

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

src/string_with_vars.ml

@@ -208,6 +208,15 @@ module Var = struct
     match destruct t with
     | Single s -> s
     | Pair (k, v) -> k ^ ":" ^ v
+
+  let to_string = string_of_var
+
+  let fail v ~f = Loc.fail (loc v) "%s" (f (to_string v))
+
+  let sexp_of_t t = Sexp.atom (to_string t)
+
+  let rename t ~new_name =
+    { t with name = new_name }
 end
 
 let partial_expand

src/string_with_vars.mli

@@ -49,6 +49,8 @@ end
 module Var : sig
   type t
 
+  val sexp_of_t : t -> Sexp.t
+
   val loc : t -> Loc.t
   val full_name : t -> string
 
@@ -57,6 +59,12 @@ module Var : sig
     | Pair of string * string
 
   val destruct : t -> kind
+
+  val fail : t -> f:(string -> string) -> _
+
+  val to_string : t -> string
+
+  val rename : t -> new_name:string -> t
 end
 
 val expand