[sledge] Refactor: Add Option.Import including Monad_infix and Monad_syntax

Summary:
The convention is for modules that are intended to be `open`ed, that
define syntax and infix operations, are named `Import`. This diff
combines the `Option.Monad_infix` and `Option.Monad_syntax` modules
into `Option.Import` to follow this convention.

Reviewed By: ngorogiannis

Differential Revision: D22170507

fbshipit-source-id: 44378fd56

sledge/nonstdlib/NS.ml

@@ -76,8 +76,7 @@ end
 (** Containers *)
 
 module Option = Option
-include Option.Monad_infix
-include Option.Monad_syntax
+include Option.Import
 module List = List
 
 module Array = struct

sledge/nonstdlib/NS.mli

@@ -73,8 +73,7 @@ module Invariant : module type of Core.Invariant
 (** Containers *)
 
 module Option = Option
-include module type of Option.Monad_infix
-include module type of Option.Monad_syntax
+include module type of Option.Import
 module List = List
 
 module Array : sig

sledge/nonstdlib/option.ml

@@ -21,3 +21,8 @@ module Monad_syntax = struct
   let ( let* ) x f = bind ~f x
   let ( and* ) x y = both x y
 end
+
+module Import = struct
+  include Monad_infix
+  include Monad_syntax
+end

sledge/nonstdlib/option.mli

@@ -16,4 +16,7 @@ val or_else : f:(unit -> 'a option) -> 'a option -> 'a option
 
 val cons : 'a t -> 'a list -> 'a list
 
-module Monad_syntax : Monad_syntax with type 'a t := 'a option
+module Import : sig
+  include Monad_syntax with type 'a t := 'a option
+  include module type of Monad_infix
+end

sledge/src/exec.ml

@@ -637,7 +637,7 @@ let strlen_spec reg ptr =
  * Symbolic Execution
  *)
 
-open Option.Monad_syntax
+open Option.Import
 
 let check_preserve_us (q0 : Sh.t) (q1 : Sh.t) =
   let gain_us = Var.Set.diff q1.us q0.us in