Write explicit interface for Expand_to

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

src/string_with_vars.ml

@@ -131,7 +131,28 @@ module Expand = struct
   end
 end
 
+module type Expand_intf = sig
+  type context
+  type expansion
+
+  val expand
+    :  context
+    -> t
+    -> allow_multivalue:bool
+    -> f:(Loc.t -> string -> expansion option)
+    -> expansion Expand.Full.t
+
+  val partial_expand
+    :  context
+    -> t
+    -> allow_multivalue:bool
+    -> f:(Loc.t -> string -> expansion option)
+    -> expansion Expand.Partial.t
+end
+
 module Expand_to(V: EXPANSION) = struct
+  type expansion = V.t
+  type context = V.context
 
   let check_valid_multivalue syntax ~var t x =
     if not t.quoted && V.is_multivalued x then

src/string_with_vars.mli

@@ -79,24 +79,27 @@ module Expand : sig
   end
 end
 
-module Expand_to(V : EXPANSION) : sig
+module type Expand_intf = sig
+  type context
+  type expansion
+
   val expand
-    :  V.context
+    :  context
     -> t
     -> allow_multivalue:bool
-    -> f:(Loc.t -> string -> V.t option)
-    -> V.t Expand.Full.t
+    -> f:(Loc.t -> string -> expansion option)
+    -> expansion 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
+    :  context
     -> t
     -> allow_multivalue:bool
-    -> f:(Loc.t -> string -> V.t option)
-    -> V.t Expand.Partial.t
+    -> f:(Loc.t -> string -> expansion option)
+    -> expansion 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
@@ -104,6 +107,9 @@ module Expand_to(V : EXPANSION) : sig
         least a variable of [t], it returns a string-with-vars. *)
 end
 
+module Expand_to(V : EXPANSION) : Expand_intf
+  with type expansion = V.t and type context = V.context
+
 val expand
   :  t
   -> f:(Loc.t -> string -> string option)