diff --git a/src/action.ml b/src/action.ml
index 4cc10353..d112621c 100644
--- a/src/action.ml
+++ b/src/action.ml
@@ -374,8 +374,8 @@ module Unexpanded = struct
         | Left x -> map x
         | Right template ->
            match To_VE.expand dir template ~f with
-           | Left  e -> special dir e
-           | Right s -> generic dir s
+           | Expansion e -> special dir e
+           | String    s -> generic dir s
       [@@inlined always]
 
       let string ~dir ~f x =
@@ -465,9 +465,9 @@ module Unexpanded = struct
   module E = struct
     let expand ~generic ~special ~dir ~f template =
       match To_VE.partial_expand dir template ~f with
-      | Left (Left  e) -> Left (special dir e)
-      | Left (Right s) -> Left (generic dir s)
-      | Right _ as x -> x
+      | Expansion e -> Left (special dir e)
+      | String s -> Left (generic dir s)
+      | Unexpanded x -> Right x
 
     let string ~dir ~f x =
       expand ~dir ~f x
diff --git a/src/string_with_vars.ml b/src/string_with_vars.ml
index c1593165..605bb458 100644
--- a/src/string_with_vars.ml
+++ b/src/string_with_vars.ml
@@ -116,6 +116,20 @@ let concat_rev = function
   | [s] -> s
   | l -> String.concat (List.rev l) ~sep:""
 
+module Expand = struct
+  module Full = struct
+    type nonrec 'a t =
+      | Expansion  of 'a
+      | String     of string
+  end
+  module Partial = struct
+    type nonrec 'a t =
+      | Expansion  of 'a
+      | String     of string
+      | Unexpanded of t
+  end
+end
+
 module Expand_to(V: EXPANSION) = struct
 
   let expand ctx t ~f =
@@ -123,10 +137,10 @@ module Expand_to(V: EXPANSION) = struct
     | [Var (syntax, v)] when not t.quoted ->
       (* Unquoted single var *)
       (match f t.loc v with
-       | Some e -> Left e
-       | None -> Right (string_of_var syntax v))
+       | Some e -> Expand.Full.Expansion e
+       | None -> Expand.Full.String (string_of_var syntax v))
     | _ ->
-      Right (List.map t.items ~f:(function
+      Expand.Full.String (List.map t.items ~f:(function
         | Text s -> s
         | Var (syntax, v) ->
           match f t.loc v with
@@ -137,7 +151,7 @@ module Expand_to(V: EXPANSION) = struct
                 (string_of_var syntax v)
             else V.to_string ctx x
           | None -> string_of_var syntax v)
-             |> String.concat ~sep:"")
+               |> String.concat ~sep:"")
 
   let partial_expand ctx t ~f =
     let commit_text acc_text acc =
@@ -148,8 +162,8 @@ module Expand_to(V: EXPANSION) = struct
       match items with
       | [] -> begin
           match acc with
-          | [] -> Left  (Right (concat_rev acc_text))
-          | _  -> Right { t with items = List.rev (commit_text acc_text acc) }
+          | [] -> Expand.Partial.String (concat_rev acc_text)
+          | _  -> Unexpanded { t with items = List.rev (commit_text acc_text acc) }
         end
       | Text s :: items -> loop (s :: acc_text) acc items
       | Var (syntax, v) as it :: items ->
@@ -165,8 +179,8 @@ module Expand_to(V: EXPANSION) = struct
     | [Var (_, v)] when not t.quoted ->
       (* Unquoted single var *)
       (match f t.loc v with
-       | Some e -> Left (Left e)
-       | None   -> Right t)
+       | Some e -> Expand.Partial.Expansion e
+       | None   -> Expand.Partial.Unexpanded t)
     | _ -> loop [] [] t.items
 end
 
@@ -180,12 +194,15 @@ end
 module S = Expand_to(String_expansion)
 
 let expand t ~f =
-  match S.expand () t ~f with Left s | Right s -> s
+  match S.expand () t ~f with
+  | Expand.Full.String s
+  | Expansion s -> s
 
 let partial_expand t ~f =
   match S.partial_expand () t ~f with
-  | Left (Left s | Right s) -> Left s
-  | Right _ as x -> x
+  | Expand.Partial.Expansion s -> Left s
+  | String s -> Left s
+  | Unexpanded s -> Right s
 
 let to_string t =
   match t.items with
diff --git a/src/string_with_vars.mli b/src/string_with_vars.mli
index 4bde6edb..9dc3ab38 100644
--- a/src/string_with_vars.mli
+++ b/src/string_with_vars.mli
@@ -63,17 +63,36 @@ module type EXPANSION = sig
       using [to_string]. *)
 end
 
+module Expand : sig
+  module Full : sig
+    type nonrec 'a t =
+      | Expansion  of 'a
+      | String     of string
+  end
+  module Partial : sig
+    type nonrec 'a t =
+      | Expansion  of 'a
+      | String     of string
+      | Unexpanded of t
+  end
+end
+
 module Expand_to(V : EXPANSION) : sig
-  val expand : V.context -> t -> f:(Loc.t -> string -> V.t option) ->
-    (V.t, string) Either.t
+  val expand
+    :  V.context
+    -> t
+    -> f:(Loc.t -> string -> V.t option)
+    -> V.t Expand.Full.t
   (** [expand t ~f] return [t] where all variables have been expanded
       using [f].  If [f loc var] return [Some x], the variable [var] is
       replaced by [x]; otherwise, the variable is inserted using the syntax
       it was originally defined with: ${..} or $(..) *)
 
-  val partial_expand :
-    V.context -> t -> f:(Loc.t -> string -> V.t option) ->
-    ((V.t, string) either, t) Either.t
+  val partial_expand
+    :  V.context
+    -> t
+    -> f:(Loc.t -> string -> V.t option)
+    -> V.t Expand.Partial.t
     (** [partial_expand t ~f] is like [expand_generic] where all
         variables that could be expanded (i.e., those for which [f]
         returns [Some _]) are.  If all the variables of [t] were