refactor: replace >>= with let* where possible (#8529)

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

bin/describe/describe_workspace.ml

@@ -446,10 +446,12 @@ module Crawl = struct
         match Lib.is_local lib with
         | false -> Memo.return []
         | true ->
-          Dir_contents.get sctx ~dir:(Path.as_in_build_dir_exn src_dir)
-          >>= Dir_contents.ocaml
-          >>| Ml_sources.modules_and_obj_dir ~for_:(Library name)
-          >>= fun (modules_, obj_dir_) ->
+          (* XXX why do we have a second object directory? *)
+          let* modules_, obj_dir_ =
+            Dir_contents.get sctx ~dir:(Path.as_in_build_dir_exn src_dir)
+            >>= Dir_contents.ocaml
+            >>| Ml_sources.modules_and_obj_dir ~for_:(Library name)
+          in
           let pp_map =
             Staged.unstage
             @@

src/dune_rules/coq/coq_rules.ml

@@ -478,8 +478,7 @@ let deps_of ~dir ~boot_type ~wrapper_name ~mode coq_module =
     in
     Path.set_extension ~ext (Coq_module.source coq_module)
   in
-  get_dep_map ~dir ~wrapper_name
-  >>= fun dep_map ->
+  let* dep_map = get_dep_map ~dir ~wrapper_name in
   match Dep_map.find dep_map vo_target with
   | None ->
     Code_error.raise

src/dune_rules/dune_project.ml

@@ -583,7 +583,7 @@ module Toggle = struct
     let decode =
       match check with
       | None -> decode
-      | Some check -> check >>= fun () -> decode
+      | Some check -> check >>> decode
     in
     field_o name decode
   ;;

src/dune_rules/workspace.ml

@@ -300,9 +300,7 @@ module Context = struct
     let decode =
       let+ common = Common.decode
       and+ name =
-        field_o
-          "name"
-          (Dune_lang.Syntax.since syntax (1, 10) >>= fun () -> Context_name.decode)
+        field_o "name" (Dune_lang.Syntax.since syntax (1, 10) >>> Context_name.decode)
       and+ lock =
         (* TODO
            1. guard before version check before releasing

test/expect-tests/dune_file_watcher/dune_file_watcher_tests_lib.ml

@@ -46,8 +46,7 @@ let get_events ~try_to_get_events ~expected =
       assert (n > 0);
       retry_loop ~period:0.01 ~timeout:3.0 ~f:(fun () ->
         let open Option.O in
-        try_to_get_events ()
-        >>= fun events ->
+        let* events = try_to_get_events () in
         collected := !collected @ events;
         if List.length !collected >= expected then Some `Enough else None)
   in

test/expect-tests/memo/memoize_tests.ml

@@ -408,7 +408,12 @@ let%expect_test "fib linked list" =
   let seventh = run (Memo.exec memo 7) in
   printf "7th: %d\n" seventh.value;
   printf "prev: %d\n" (run (force seventh.prev_cell)).value;
-  printf "prev: %d\n" (run (force seventh.prev_cell >>= fun x -> force x.prev_cell)).value;
+  printf
+    "prev: %d\n"
+    (run
+       (let* x = force seventh.prev_cell in
+        force x.prev_cell))
+      .value;
   [%expect
     {|
     computing 4