diff --git a/infer/src/IR/AttributesTable.re b/infer/src/IR/AttributesTable.re
index d34535719..657c6c06a 100644
--- a/infer/src/IR/AttributesTable.re
+++ b/infer/src/IR/AttributesTable.re
@@ -30,7 +30,7 @@ let res_dir_attr_filename defined::defined pname => {
     if (len < 2) {
       Filename.current_dir_name
     } else {
-      String.sub base (len - 2) 2
+      String.sub base pos::(len - 2) len::2
     }
   };
   let filename =
@@ -144,7 +144,7 @@ let is_whitelisted_cpp_method method_name =>
         IList.for_all
           (
             fun whitelisting_class_substring =>
-              Utils.string_contains whitelisting_class_substring method_name
+              String.is_substring substring::whitelisting_class_substring method_name
           )
           whitelisting_class
     )
diff --git a/infer/src/IR/Ident.re b/infer/src/IR/Ident.re
index 6e94b1983..ef302acf4 100644
--- a/infer/src/IR/Ident.re
+++ b/infer/src/IR/Ident.re
@@ -138,10 +138,10 @@ let fieldname_to_complete_string fn => Mangled.to_string_full fn.fname;
 /** Convert a fieldname to a simplified string with at most one-level path. */
 let fieldname_to_simplified_string fn => {
   let s = Mangled.to_string fn.fname;
-  switch (string_split_character s '.') {
-  | (Some s1, s2) =>
-    switch (string_split_character s1 '.') {
-    | (Some _, s4) => s4 ^ "." ^ s2
+  switch (String.rsplit2 s on::'.') {
+  | Some (s1, s2) =>
+    switch (String.rsplit2 s1 on::'.') {
+    | Some (_, s4) => s4 ^ "." ^ s2
     | _ => s
     }
   | _ => s
@@ -152,8 +152,8 @@ let fieldname_to_simplified_string fn => {
 /** Convert a fieldname to a flat string without path. */
 let fieldname_to_flat_string fn => {
   let s = Mangled.to_string fn.fname;
-  switch (string_split_character s '.') {
-  | (Some _, s2) => s2
+  switch (String.rsplit2 s on::'.') {
+  | Some (_, s2) => s2
   | _ => s
   }
 };
@@ -162,16 +162,16 @@ let fieldname_to_flat_string fn => {
 /** Returns the class part of the fieldname */
 let java_fieldname_get_class fn => {
   let fn = fieldname_to_string fn;
-  let ri = String.rindex fn '.';
-  String.sub fn 0 ri
+  let ri = String.rindex_exn fn '.';
+  String.slice fn 0 ri
 };
 
 
 /** Returns the last component of the fieldname */
 let java_fieldname_get_field fn => {
   let fn = fieldname_to_string fn;
-  let ri = 1 + String.rindex fn '.';
-  String.sub fn ri (String.length fn - ri)
+  let ri = 1 + String.rindex_exn fn '.';
+  String.slice fn ri 0
 };
 
 
@@ -179,12 +179,12 @@ let java_fieldname_get_field fn => {
 let java_fieldname_is_outer_instance fn => {
   let fn = fieldname_to_string fn;
   let fn_len = String.length fn;
-  let this = ".this$";
-  let this_len = String.length this;
-  let zero_to_nine s => s >= "0" && s <= "9";
-  fn_len > this_len &&
-  String.sub fn (fn_len - this_len - 1) this_len == this &&
-  zero_to_nine (String.sub fn (fn_len - 1) 1)
+  fn_len != 0 && {
+    let this = ".this$";
+    let last_char = fn.[fn_len - 1];
+    (last_char >= '0' && last_char <= '9') &&
+    String.is_suffix fn suffix::(this ^ String.of_char last_char)
+  }
 };
 
 let fieldname_offset fn => fn.fpos;
diff --git a/infer/src/IR/Io_infer.ml b/infer/src/IR/Io_infer.ml
index 4b619da7d..e2ffd4b90 100644
--- a/infer/src/IR/Io_infer.ml
+++ b/infer/src/IR/Io_infer.ml
@@ -190,7 +190,7 @@ struct
   (** Print an html link to the given node. *)
   let pp_node_link path_to_root pname ~description ~preds ~succs ~exn ~isvisited ~isproof fmt id =
     let display_name =
-      (if description = "" then "N" else String.sub description 0 1)
+      (if description = "" then "N" else String.sub description ~pos:0 ~len:1)
       ^ "_"
       ^ (string_of_int id) in
     let node_fname = node_filename pname id in
diff --git a/infer/src/IR/Localise.ml b/infer/src/IR/Localise.ml
index d20ab3b41..01ed5b1b2 100644
--- a/infer/src/IR/Localise.ml
+++ b/infer/src/IR/Localise.ml
@@ -500,7 +500,7 @@ let dereference_string deref_str value_str access_opt loc =
     | Some (Returned_from_call _) -> true
     | _ -> false in
   let value_desc =
-    String.concat "" [
+    String.concat ~sep:"" [
       (match deref_str.value_pre with Some s -> s ^ " " | _ -> "");
       (if is_call_access then "returned by " else "");
       value_str;
diff --git a/infer/src/IR/Objc_models.ml b/infer/src/IR/Objc_models.ml
index 125c31c5c..beea48add 100644
--- a/infer/src/IR/Objc_models.ml
+++ b/infer/src/IR/Objc_models.ml
@@ -201,8 +201,8 @@ struct
     | Core_graphics -> core_graphics_types
 
   let is_objc_memory_model_controlled o =
-    IList.mem Core.Std.String.equal o core_foundation_types ||
-    IList.mem Core.Std.String.equal o core_graphics_types
+    IList.mem String.equal o core_foundation_types ||
+    IList.mem String.equal o core_graphics_types
 
   let rec is_core_lib lib typ =
     match typ with
@@ -210,7 +210,7 @@ struct
         is_core_lib lib styp
     | Typ.Tstruct name ->
         let core_lib_types = core_lib_to_type_list lib in
-        IList.mem Core.Std.String.equal (Typename.name name) core_lib_types
+        IList.mem String.equal (Typename.name name) core_lib_types
     | _ -> false
 
   let is_core_foundation_type typ =
@@ -225,11 +225,11 @@ struct
 
   let is_core_lib_create typ funct =
     is_core_lib_type typ &&
-    ((string_contains create funct) ||
-     (string_contains copy funct ))
+    ((String.is_substring ~substring:create funct) ||
+     (String.is_substring ~substring:copy funct ))
 
   let function_arg_is_cftype typ =
-    (string_contains cf_type typ)
+    (String.is_substring ~substring:cf_type typ)
 
   let is_core_lib_retain typ funct =
     function_arg_is_cftype typ && funct = cf_retain
@@ -241,12 +241,12 @@ struct
     try
       let cg_typ = IList.find
           (fun lib -> (funct = (lib^upper_release))) core_graphics_types in
-      (string_contains (cg_typ^ref) typ)
+      (String.is_substring ~substring:(cg_typ^ref) typ)
     with Not_found -> false
 
 (*
   let function_arg_is_core_pgraphics typ =
-    let res = (string_contains cf_type typ) in
+    let res = (String.is_substring ~substring:cf_type typ) in
     res
 *)
 end
diff --git a/infer/src/IR/Procname.re b/infer/src/IR/Procname.re
index 34fa994cf..a964d014c 100644
--- a/infer/src/IR/Procname.re
+++ b/infer/src/IR/Procname.re
@@ -127,7 +127,11 @@ let java_return_type_to_string j verbosity =>
 
 /** Given a package.class_name string, it looks for the latest dot and split the string
     in two (package, class_name) */
-let split_classname package_classname => string_split_character package_classname '.';
+let split_classname package_classname =>
+  switch (String.rsplit2 package_classname on::'.') {
+  | Some (x, y) => (Some x, y)
+  | None => (None, package_classname)
+  };
 
 let from_string_c_fun (s: string) => C (s, None);
 
@@ -308,17 +312,17 @@ let java_to_string withclass::withclass=false (j: java) verbosity =>
 
 /** Check if the class name is for an anonymous inner class. */
 let is_anonymous_inner_class_name class_name =>
-  switch (string_split_character class_name '$') {
-  | (Some _, s) =>
+  switch (String.rsplit2 class_name on::'$') {
+  | Some (_, s) =>
     let is_int =
       try {
-        ignore (int_of_string (String.trim s));
+        ignore (int_of_string (String.strip s));
         true
       } {
       | Failure _ => false
       };
     is_int
-  | (None, _) => false
+  | None => false
   };
 
 
@@ -362,8 +366,8 @@ let java_is_anonymous_inner_class_constructor =
 let java_is_access_method =
   fun
   | Java js =>
-    switch (string_split_character js.method_name '$') {
-    | (Some "access", s) =>
+    switch (String.rsplit2 js.method_name on::'$') {
+    | Some ("access", s) =>
       let is_int =
         try {
           ignore (int_of_string s);
@@ -395,7 +399,8 @@ let java_is_vararg =
     }
   | _ => false;
 
-let is_objc_constructor method_name => method_name == "new" || string_is_prefix "init" method_name;
+let is_objc_constructor method_name =>
+  method_name == "new" || String.is_prefix prefix::"init" method_name;
 
 let is_objc_kind =
   fun
@@ -449,9 +454,9 @@ let is_infer_undefined pn =>
 
 let get_global_name_of_initializer =
   fun
-  | C (name, _) when string_is_prefix Config.clang_initializer_prefix name => {
+  | C (name, _) when String.is_prefix prefix::Config.clang_initializer_prefix name => {
       let prefix_len = String.length Config.clang_initializer_prefix;
-      Some (String.sub name prefix_len (String.length name - prefix_len))
+      Some (String.sub name pos::prefix_len len::(String.length name - prefix_len))
     }
   | _ => None;
 
diff --git a/infer/src/IR/Pvar.re b/infer/src/IR/Pvar.re
index 4b4f9501d..4374fbfa1 100644
--- a/infer/src/IR/Pvar.re
+++ b/infer/src/IR/Pvar.re
@@ -175,10 +175,10 @@ let to_string pv => Mangled.to_string pv.pv_name;
 
 let get_simplified_name pv => {
   let s = Mangled.to_string pv.pv_name;
-  switch (string_split_character s '.') {
-  | (Some s1, s2) =>
-    switch (string_split_character s1 '.') {
-    | (Some _, s4) => s4 ^ "." ^ s2
+  switch (String.rsplit2 s on::'.') {
+  | Some (s1, s2) =>
+    switch (String.rsplit2 s1 on::'.') {
+    | Some (_, s4) => s4 ^ "." ^ s2
     | _ => s
     }
   | _ => s
@@ -253,10 +253,11 @@ let tmp_prefix = "0$?%__sil_tmp";
 let is_frontend_tmp pvar => {
   /* Check whether the program variable is a temporary one generated by sawja */
   let is_sawja_tmp name =>
-    string_is_prefix "$irvar" name ||
-    string_is_prefix "$T" name || string_is_prefix "$bc" name || string_is_prefix "CatchVar" name;
+    String.is_prefix prefix::"$irvar" name ||
+    String.is_prefix prefix::"$T" name ||
+    String.is_prefix prefix::"$bc" name || String.is_prefix prefix::"CatchVar" name;
   /* Check whether the program variable is generated by [mk_tmp] */
-  let is_sil_tmp name => string_is_prefix tmp_prefix name;
+  let is_sil_tmp name => String.is_prefix prefix::tmp_prefix name;
   let name = to_string pvar;
   is_sil_tmp name || (
     switch pvar.pv_kind {
diff --git a/infer/src/IR/Typ.re b/infer/src/IR/Typ.re
index 2f79d74c8..826d61e13 100644
--- a/infer/src/IR/Typ.re
+++ b/infer/src/IR/Typ.re
@@ -283,7 +283,7 @@ let rec java_from_string =
   | "float" => Tfloat FFloat
   | "double" => Tfloat FDouble
   | typ_str when String.contains typ_str '[' => {
-      let stripped_typ = String.sub typ_str 0 (String.length typ_str - 2);
+      let stripped_typ = String.sub typ_str pos::0 len::(String.length typ_str - 2);
       Tptr (Tarray (java_from_string stripped_typ) None) Pk_pointer
     }
   | typ_str => Tstruct (Typename.Java.from_string typ_str);
diff --git a/infer/src/backend/InferPrint.re b/infer/src/backend/InferPrint.re
index 06108e64f..0470bdfd4 100644
--- a/infer/src/backend/InferPrint.re
+++ b/infer/src/backend/InferPrint.re
@@ -345,7 +345,7 @@ let should_report (issue_kind: Exceptions.err_kind) issue_type error_desc =>
             let eq o y =>
               switch (o, y) {
               | (None, _) => false
-              | (Some x, y) => Core.Std.String.equal x y
+              | (Some x, y) => String.equal x y
               };
             IList.mem eq issue_bucket high_buckets
           };
@@ -1152,7 +1152,7 @@ let pp_json_report_by_report_kind formats_by_report_kind fname =>
       IList.iter pp_json_issue format_list
     };
     let sorted_report = {
-      let report = Jsonbug_j.report_of_string (String.concat "\n" report_lines);
+      let report = Jsonbug_j.report_of_string (String.concat sep::"\n" report_lines);
       IList.sort tests_jsonbug_compare report
     };
     let pp_report_by_report_kind (report_kind, format_list) =>
@@ -1260,7 +1260,7 @@ let module AnalysisResults = {
 
   /** Create an iterator which loads spec files one at a time */
   let iterator_of_spec_files () => {
-    let sorted_spec_files = IList.sort Core.Std.String.compare (spec_files_from_cmdline ());
+    let sorted_spec_files = IList.sort String.compare (spec_files_from_cmdline ());
     let do_spec f fname =>
       switch (Specs.load_summary (DB.filename_from_string fname)) {
       | None =>
diff --git a/infer/src/backend/clusterMakefile.ml b/infer/src/backend/clusterMakefile.ml
index 24a0a4614..49f5af86d 100644
--- a/infer/src/backend/clusterMakefile.ml
+++ b/infer/src/backend/clusterMakefile.ml
@@ -39,7 +39,7 @@ let cluster_should_be_analyzed cluster =
 let pp_prolog fmt clusters =
   let compilation_dbs_cmd =
     IList.map (F.sprintf "--clang-compilation-db-files %s") !Config.clang_compilation_db_files
-    |> String.concat " " in
+    |> String.concat ~sep:" " in
   F.fprintf fmt "INFERANALYZE= %s -results_dir '%s' %s \n@."
     (Config.bin_dir // (CLOpt.exe_name Analyze))
     (Escape.escape_map
diff --git a/infer/src/backend/crashcontext.ml b/infer/src/backend/crashcontext.ml
index 6ea328c57..80c5a0331 100644
--- a/infer/src/backend/crashcontext.ml
+++ b/infer/src/backend/crashcontext.ml
@@ -74,7 +74,7 @@ let collect_all_summaries root_summaries_dir stacktrace_file stacktraces_dir =
       (fun summaries path ->
          (* check if the file is a JSON file under the crashcontext dir *)
          if not (Sys.is_directory path) && Filename.check_suffix path "json" &&
-            string_is_suffix "crashcontext" (Filename.dirname path)
+            String.is_suffix ~suffix:"crashcontext" (Filename.dirname path)
          then path :: summaries
          else summaries)
       []
diff --git a/infer/src/backend/errdesc.ml b/infer/src/backend/errdesc.ml
index cbf2005f5..84a1f07a6 100644
--- a/infer/src/backend/errdesc.ml
+++ b/infer/src/backend/errdesc.ml
@@ -21,7 +21,7 @@ let vector_class = ["std"; "vector"]
 let is_one_of_classes class_name classes =
   IList.exists (fun wrapper_class ->
       IList.for_all (fun wrapper_class_substring ->
-          Utils.string_contains wrapper_class_substring class_name) wrapper_class)
+          String.is_substring ~substring:wrapper_class_substring class_name) wrapper_class)
     classes
 
 let is_method_of_objc_cpp_class pname classes =
@@ -38,7 +38,7 @@ let is_special_field class_names field_name_opt field =
   let complete_fieldname = Ident.fieldname_to_complete_string field in
   let field_ok =
     match field_name_opt with
-    | Some field_name -> Utils.string_contains field_name complete_fieldname
+    | Some field_name -> String.is_substring ~substring:field_name complete_fieldname
     | None -> true in
   is_one_of_classes complete_fieldname class_names && field_ok
 
diff --git a/infer/src/backend/infer.ml b/infer/src/backend/infer.ml
index 12f87ed81..a179caebf 100644
--- a/infer/src/backend/infer.ml
+++ b/infer/src/backend/infer.ml
@@ -88,7 +88,7 @@ let clean_results_dir () =
         let rec cleandir dir =
           match Unix.readdir dir with
           | entry ->
-              if (IList.exists (Core.Std.String.equal entry) dirs) then (
+              if (IList.exists (String.equal entry) dirs) then (
                 rmtree (name // entry)
               ) else if not (entry = Filename.current_dir_name
                              || entry = Filename.parent_dir_name) then (
@@ -132,7 +132,7 @@ let run_command cmd_list after_wait =
   let exit_code = match status with Unix.WEXITED i -> i | _ -> 1 in
   after_wait exit_code ;
   if exit_code <> 0 then (
-    L.do_err "Failed to execute: %s@\n" (String.concat " " cmd_list) ;
+    L.do_err "Failed to execute: %s@\n" (String.concat ~sep:" " cmd_list) ;
     exit exit_code
   )
 
@@ -306,7 +306,7 @@ let fail_on_issue_epilogue () =
   let issues_json = DB.Results_dir.(path_to_filename Abs_root ["report.json"]) in
   match read_file (DB.filename_to_string issues_json) with
   | Some lines ->
-      let issues = Jsonbug_j.report_of_string @@ String.concat "" lines in
+      let issues = Jsonbug_j.report_of_string @@ String.concat ~sep:"" lines in
       if issues <> [] then exit Config.fail_on_issue_exit_code
   | None -> ()
 
diff --git a/infer/src/backend/inferconfig.ml b/infer/src/backend/inferconfig.ml
index 3d28246ec..f227eef94 100644
--- a/infer/src/backend/inferconfig.ml
+++ b/infer/src/backend/inferconfig.ml
@@ -79,7 +79,7 @@ module FileContainsStringMatcher = struct
     else
       let source_map = ref SourceFile.Map.empty in
       let regexp =
-        Str.regexp (join_strings "\\|" s_patterns) in
+        Str.regexp (String.concat ~sep:"\\|" s_patterns) in
       fun source_file ->
         try
           SourceFile.Map.find source_file !source_map
@@ -124,7 +124,7 @@ module FileOrProcMatcher = struct
             (fun p ->
                match p.Config.method_name with
                | None -> true
-               | Some m -> Core.Std.String.equal m method_name)
+               | Some m -> String.equal m method_name)
             class_patterns
         with Not_found -> false in
 
@@ -221,7 +221,7 @@ let filters_from_inferconfig inferconfig : filters =
   let error_filter =
     function error_name ->
       let error_str = Localise.to_string error_name in
-      not (IList.exists (Core.Std.String.equal error_str) inferconfig.suppress_errors) in
+      not (IList.exists (String.equal error_str) inferconfig.suppress_errors) in
   {
     path_filter = path_filter;
     error_filter = error_filter;
@@ -265,7 +265,7 @@ let test () =
          let source_file = SourceFile.from_abs_path path in
          let matching = matching_analyzers source_file in
          if matching <> [] then
-           let matching_s = join_strings ", " (IList.map fst matching) in
+           let matching_s = String.concat ~sep:", " (IList.map fst matching) in
            L.stderr "%s -> {%s}@."
              (SourceFile.to_rel_path source_file)
              matching_s)
diff --git a/infer/src/backend/printer.ml b/infer/src/backend/printer.ml
index 21ce935e4..638d82237 100644
--- a/infer/src/backend/printer.ml
+++ b/infer/src/backend/printer.ml
@@ -34,7 +34,7 @@ struct
         let line =
           let len = String.length line_raw in
           if len > 0 && String.get line_raw (len -1) = '\013' then
-            String.sub line_raw 0 (len -1)
+            String.sub line_raw ~pos:0 ~len:(len -1)
           else line_raw in
         lines := line :: !lines
       done;
diff --git a/infer/src/backend/rearrange.ml b/infer/src/backend/rearrange.ml
index 3cc80269f..3f54484e1 100644
--- a/infer/src/backend/rearrange.ml
+++ b/infer/src/backend/rearrange.ml
@@ -624,15 +624,10 @@ let add_guarded_by_constraints tenv prop lexp pdesc =
       lowercase_str = "ui_thread" || lowercase_str = "ui-thread" || lowercase_str = "uithread" in
     is_invalid_exp_str str || is_ui_thread str in
   let guarded_by_str_is_this guarded_by_str =
-    string_is_suffix "this" guarded_by_str in
+    String.is_suffix ~suffix:"this" guarded_by_str in
   let guarded_by_str_is_class guarded_by_str class_str =
-    let dollar_normalize s =
-      String.map
-        (function
-          | '$' -> '.'
-          | c -> c)
-        s in
-    string_is_suffix (dollar_normalize guarded_by_str) (dollar_normalize (class_str ^ ".class")) in
+    let dollar_normalize s = String.map s ~f:(function '$' -> '.' | c -> c) in
+    String.is_suffix ~suffix:(dollar_normalize guarded_by_str) (dollar_normalize (class_str ^ ".class")) in
   let guarded_by_str_is_current_class guarded_by_str = function
     | Procname.Java java_pname ->
         (* programmers write @GuardedBy("MyClass.class") when the field is guarded by the class *)
@@ -642,7 +637,7 @@ let add_guarded_by_constraints tenv prop lexp pdesc =
   let guarded_by_str_is_class_this class_name guarded_by_str =
     let fully_qualified_this =
       Printf.sprintf "%s.this" class_name in
-    string_is_suffix guarded_by_str fully_qualified_this
+    String.is_suffix ~suffix:guarded_by_str fully_qualified_this
   in
 
   (* return true if [guarded_by_str] is a suffix of "<name_of_super_class>.this" *)
@@ -719,11 +714,11 @@ let add_guarded_by_constraints tenv prop lexp pdesc =
        of the object of type T in the current state." note that this is ambiguous when there are
        multiple objects of type T, but let's try to respect the intention *)
     let match_on_field_type typ flds =
-      match string_split_character guarded_by_str0 '.' with
-      | Some class_part, field_part ->
+      match String.rsplit2 guarded_by_str0 ~on:'.' with
+      | Some (class_part, field_part) ->
           let typ_matches_guarded_by _ = function
             | Typ.Tptr (ptr_typ, _) ->
-                string_is_suffix class_part (Typ.to_string ptr_typ);
+                String.is_suffix ~suffix:class_part (Typ.to_string ptr_typ);
             | _ ->
                 false in
           begin
@@ -797,8 +792,8 @@ let add_guarded_by_constraints tenv prop lexp pdesc =
       let exn = Exceptions.Unsafe_guarded_by_access (err_desc, __POS__) in
       Reporting.log_error pname exn in
     let rec is_read_write_lock typ =
-      let str_is_read_write_lock str = string_is_suffix "ReadWriteUpdateLock" str ||
-                                       string_is_suffix "ReadWriteLock" str  in
+      let str_is_read_write_lock str = String.is_suffix ~suffix:"ReadWriteUpdateLock" str ||
+                                       String.is_suffix ~suffix:"ReadWriteLock" str  in
       match typ with
       | Typ.Tstruct name -> str_is_read_write_lock (Typename.name name)
       | Typ.Tptr (typ, _) -> is_read_write_lock typ
@@ -818,8 +813,8 @@ let add_guarded_by_constraints tenv prop lexp pdesc =
           | _ -> false)
         (Attribute.get_for_exp tenv prop guarded_by_exp) in
     let guardedby_is_self_referential =
-      Core.Std.String.equal "itself" (String.lowercase guarded_by_str) ||
-      string_is_suffix guarded_by_str (Ident.fieldname_to_string accessed_fld) in
+      String.equal "itself" (String.lowercase guarded_by_str) ||
+      String.is_suffix ~suffix:guarded_by_str (Ident.fieldname_to_string accessed_fld) in
     let proc_has_suppress_guarded_by_annot pdesc =
       let proc_signature =
         Annotations.get_annotated_signature (Procdesc.get_attributes pdesc) in
diff --git a/infer/src/base/CommandLineOption.ml b/infer/src/base/CommandLineOption.ml
index 50208222e..12a8b6152 100644
--- a/infer/src/base/CommandLineOption.ml
+++ b/infer/src/base/CommandLineOption.ml
@@ -49,11 +49,11 @@ let dashdash long =
   | _ -> "--" ^ long
 
 let short_meta {short; meta; spec} =
-  String.concat " "
+  String.concat ~sep:" "
     ((if short = "" then [] else ["| -" ^ short]) @
      (match spec with
       | Arg.Symbol (symbols, _) ->
-          ["{ " ^ (String.concat " | " symbols) ^ " }" ^ meta]
+          ["{ " ^ (String.concat ~sep:" | " symbols) ^ " }" ^ meta]
       | _ ->
           if meta = "" then [] else ["<" ^ meta ^ ">"]))
 
@@ -85,7 +85,7 @@ let xdesc {long; short; spec; doc} =
               action arg
             else
               raise (Arg.Bad (F.sprintf "wrong argument '%s'; option '%s' expects one of: %s"
-                                arg (dashdash long) (String.concat " | " symbols)))
+                                arg (dashdash long) (String.concat ~sep:" | " symbols)))
           )
     | _ ->
         spec
@@ -138,7 +138,7 @@ let pad_and_xform doc_width left_width desc =
             wrap_line "" doc_width s
           else [s] in
         IList.map wrap_line lines in
-      let doc = indent_doc (String.concat "\n" (IList.flatten wrapped_lines)) in
+      let doc = indent_doc (String.concat ~sep:"\n" (IList.flatten wrapped_lines)) in
       xdesc {desc with doc}
 
 let align desc_list =
@@ -257,15 +257,15 @@ let mk_bool ?(deprecated_no=[]) ?(default=false) ?(f=fun b -> b)
     ?(deprecated=[]) ~long ?short ?exes ?(meta="") doc =
   let nolong =
     let len = String.length long in
-    if len > 3 && String.sub long 0 3 = "no-" then
-      String.sub long 3 (len - 3)
+    if len > 3 && String.sub long ~pos:0 ~len:3 = "no-" then
+      String.sub long ~pos:3 ~len:(len - 3)
     else
       "no-" ^ long
   and noshort =
     Option.map (fun short ->
         let len = String.length short in
-        if len > 1 && String.sub short 0 1 = "n" then
-          String.sub short 1 (len - 1)
+        if len > 1 && String.sub short ~pos:0 ~len:1 = "n" then
+          String.sub short ~pos:1 ~len:(len - 1)
         else
           "n" ^ short
       ) short
@@ -339,7 +339,7 @@ let mk_string_opt ?default ?(f=fun s -> s) ?(deprecated=[]) ~long ?short ?exes ?
 let mk_string_list ?(default=[]) ?(f=fun s -> s)
     ?(deprecated=[]) ~long ?short ?exes ?(meta="") doc =
   mk ~deprecated ~long ?short ~default ?exes ~meta doc
-    ~default_to_string:(String.concat ", ")
+    ~default_to_string:(String.concat ~sep:", ")
     ~mk_setter:(fun var str -> var := (f str) :: !var)
     ~decode_json:(list_json_decoder (string_json_decoder ~long))
     ~mk_spec:(fun set -> Arg.String set)
@@ -378,13 +378,13 @@ let mk_path_opt ?default ?(deprecated=[]) ~long ?short ?exes ?(meta="path") =
 let mk_path_list ?(default=[]) ?(deprecated=[]) ~long ?short ?exes ?(meta="path") =
   mk_path_helper
     ~setter:(fun var x -> var := x :: !var)
-    ~default_to_string:(String.concat ", ")
+    ~default_to_string:(String.concat ~sep:", ")
     ~default ~deprecated ~long ~short ~exes ~meta
 
 let mk_symbol ~default ~symbols ?(deprecated=[]) ~long ?short ?exes ?(meta="") doc =
   let strings = IList.map fst symbols in
   let sym_to_str = IList.map (fun (x,y) -> (y,x)) symbols in
-  let of_string str = IList.assoc Core.Std.String.equal str symbols in
+  let of_string str = IList.assoc String.equal str symbols in
   let to_string sym = IList.assoc ( = ) sym sym_to_str in
   mk ~deprecated ~long ?short ~default ?exes ~meta doc
     ~default_to_string:(fun s -> to_string s)
@@ -394,7 +394,7 @@ let mk_symbol ~default ~symbols ?(deprecated=[]) ~long ?short ?exes ?(meta="") d
 
 let mk_symbol_opt ~symbols ?(deprecated=[]) ~long ?short ?exes ?(meta="") doc =
   let strings = IList.map fst symbols in
-  let of_string str = IList.assoc Core.Std.String.equal str symbols in
+  let of_string str = IList.assoc String.equal str symbols in
   mk ~deprecated ~long ?short ~default:None ?exes ~meta doc
     ~default_to_string:(fun _ -> "")
     ~mk_setter:(fun var str -> var := Some (of_string str))
@@ -403,15 +403,15 @@ let mk_symbol_opt ~symbols ?(deprecated=[]) ~long ?short ?exes ?(meta="") doc =
 
 let mk_symbol_seq ?(default=[]) ~symbols ?(deprecated=[]) ~long ?short ?exes ?(meta="") doc =
   let sym_to_str = IList.map (fun (x,y) -> (y,x)) symbols in
-  let of_string str = IList.assoc Core.Std.String.equal str symbols in
+  let of_string str = IList.assoc String.equal str symbols in
   let to_string sym = IList.assoc ( = ) sym sym_to_str in
   mk ~deprecated ~long ?short ~default ?exes ~meta:(",-separated sequence" ^ meta) doc
-    ~default_to_string:(fun syms -> String.concat " " (IList.map to_string syms))
+    ~default_to_string:(fun syms -> String.concat ~sep:" " (IList.map to_string syms))
     ~mk_setter:(fun var str_seq ->
         var := IList.map of_string (Str.split (Str.regexp_string ",") str_seq))
     ~decode_json:(fun json ->
         [dashdash long;
-         String.concat "," (YBU.convert_each YBU.to_string json)])
+         String.concat ~sep:"," (YBU.convert_each YBU.to_string json)])
     ~mk_spec:(fun set -> Arg.String set)
 
 let mk_set_from_json ~default ~default_to_string ~f
@@ -453,8 +453,8 @@ let decode_inferconfig_to_argv current_exe path =
       let {decode_json} =
         IList.find
           (fun {long; short} ->
-             Core.Std.String.equal key long
-             || (* for deprecated options *) Core.Std.String.equal key short)
+             String.equal key long
+             || (* for deprecated options *) String.equal key short)
           desc_list in
       decode_json json_val @ result
     with
@@ -472,7 +472,7 @@ let decode_inferconfig_to_argv current_exe path =
 let env_var_sep = '^'
 
 let encode_argv_to_env argv =
-  String.concat (String.make 1 env_var_sep)
+  String.concat ~sep:(String.make 1 env_var_sep)
     (IList.filter (fun arg ->
          not (String.contains arg env_var_sep)
          || (
@@ -541,7 +541,9 @@ let parse ?(incomplete=false) ?(accept_unknown=false) ?config_file current_exe e
     let norm k =
       let remove_no s =
         let len = String.length k in
-        if len > 3 && String.sub s 0 3 = "no-" then String.sub s 3 (len - 3) else s in
+        if len > 3 && String.sub s ~pos:0 ~len:3 = "no-"
+        then String.sub s ~pos:3 ~len:(len - 3)
+        else s in
       let remove_weird_chars = Str.global_replace (Str.regexp "[^a-z0-9-]") "" in
       remove_weird_chars @@ String.lowercase @@ remove_no k in
     let compare_specs {long = x} {long = y} =
@@ -569,7 +571,7 @@ let parse ?(incomplete=false) ?(accept_unknown=false) ?config_file current_exe e
     let is_not_dup_with_doc speclist (opt, _, doc) =
       opt = "" ||
       IList.for_all (fun (opt', _, doc') ->
-          (doc <> "" && doc' = "") || (not (Core.Std.String.equal opt opt'))) speclist in
+          (doc <> "" && doc' = "") || (not (String.equal opt opt'))) speclist in
     let unique_exe_speclist = IList.filter (is_not_dup_with_doc !curr_speclist) exe_speclist in
     curr_speclist := IList.filter (is_not_dup_with_doc unique_exe_speclist) !curr_speclist @
                      (match header with
@@ -619,7 +621,7 @@ let parse ?(incomplete=false) ?(accept_unknown=false) ?config_file current_exe e
   (* tests if msg indicates an unknown option, as opposed to a known option with bad argument *)
   let is_unknown msg =
     let prefix = exe_name ^ ": unknown option" in
-    prefix = (String.sub msg 0 (String.length prefix)) in
+    prefix = (String.sub msg ~pos:0 ~len:(String.length prefix)) in
   let rec parse_loop () =
     try
       Arg.parse_argv_dynamic ~current:arg_being_parsed !args_to_parse curr_speclist !anon_fun
diff --git a/infer/src/base/Config.ml b/infer/src/base/Config.ml
index b40afd090..08ca4cb63 100644
--- a/infer/src/base/Config.ml
+++ b/infer/src/base/Config.ml
@@ -240,7 +240,7 @@ let real_exe_name =
 
 let current_exe =
   if !Sys.interactive then CLOpt.Interactive
-  else try IList.assoc Core.Std.String.equal (Filename.basename real_exe_name) CLOpt.exes
+  else try IList.assoc String.equal (Filename.basename real_exe_name) CLOpt.exes
     with Not_found -> CLOpt.Toplevel
 
 let bin_dir =
@@ -319,8 +319,8 @@ let patterns_of_json_with_key json_key json =
   let detect_pattern assoc =
     match detect_language assoc with
     | Ok language ->
-        let is_method_pattern key = IList.exists (Core.Std.String.equal key) ["class"; "method"]
-        and is_source_contains key = IList.exists (Core.Std.String.equal key) ["source_contains"] in
+        let is_method_pattern key = IList.exists (String.equal key) ["class"; "method"]
+        and is_source_contains key = IList.exists (String.equal key) ["source_contains"] in
         let rec loop = function
           | [] ->
               Error ("Unknown pattern for " ^ json_key ^ " in " ^ inferconfig_file)
@@ -1611,7 +1611,7 @@ let clang_frontend_do_capture, clang_frontend_do_lint =
 let analyzer = match !analyzer with Some a -> a | None -> Infer
 
 let clang_frontend_action_string =
-  String.concat " and "
+  String.concat ~sep:" and "
     ((if clang_frontend_do_capture then ["translating"] else [])
      @ (if clang_frontend_do_lint then ["linting"] else []))
 
diff --git a/infer/src/base/Latex.ml b/infer/src/base/Latex.ml
index 24f56ff6a..63f39e249 100644
--- a/infer/src/base/Latex.ml
+++ b/infer/src/base/Latex.ml
@@ -28,7 +28,7 @@ let convert_string s =
       if c == '_' then s' := !s' ^ "\\_"
       else s' := !s' ^ Char.escaped (String.get s !cnt);
       incr cnt in
-    String.iter f s;
+    String.iter ~f s;
     !s'
   end
   else s
diff --git a/infer/src/base/Process.ml b/infer/src/base/Process.ml
index 50ec02cdf..15ca23145 100644
--- a/infer/src/base/Process.ml
+++ b/infer/src/base/Process.ml
@@ -45,7 +45,7 @@ let create_process_and_wait cmd =
     | _ -> 1 in
   if exit_code <> 0 then
     print_error_and_exit ~exit_code:exit_code
-      "Failed to execute: %s\n" (String.concat " " (Array.to_list cmd))
+      "Failed to execute: %s\n" (String.concat ~sep:" " (Array.to_list cmd))
 
 (** Given a process id and a function that describes the command that the process id
     represents, prints a message explaining the command and its status, if in debug or stats mode.
diff --git a/infer/src/base/SourceFile.ml b/infer/src/base/SourceFile.ml
index 36fd8dc9f..d1e8013df 100644
--- a/infer/src/base/SourceFile.ml
+++ b/infer/src/base/SourceFile.ml
@@ -10,7 +10,7 @@
 open! Utils
 
 let count_newlines (path: string): int =
-  let open Core.Std in
+  let open! Core.Std in
   let f file = In_channel.fold_lines file ~init:0 ~f:(fun i _ -> i + 1) in
   In_channel.with_file path ~f
 
@@ -25,6 +25,7 @@ let equal sf1 sf2 =
 
 module OrderedSourceFile =
 struct
+  (* Don't use nonrec due to https://github.com/janestreet/ppx_compare/issues/2 *)
   type _t = t [@@deriving compare]
   type t = _t [@@deriving compare]
 end
@@ -35,7 +36,7 @@ module Set = Set.Make(OrderedSourceFile)
 
 let rel_path_from_abs_path root fname =
   let relative_complemented_fname = filename_to_relative root fname in
-  if string_is_prefix root fname &&
+  if String.is_prefix ~prefix:root fname &&
      Filename.is_relative relative_complemented_fname then
     Some relative_complemented_fname
   else None (* The project root is not a prefix of the file name *)
@@ -111,20 +112,20 @@ let is_infer_model source_file = match source_file with
 let is_cpp_model file =
   match file with
   | RelativeInferModel path ->
-      string_is_prefix Config.relative_cpp_models_dir path
+      String.is_prefix ~prefix:Config.relative_cpp_models_dir path
   | _ -> false
 
 let is_under_project_root = function
   | RelativeProjectRoot _ -> true
   | Absolute _ | RelativeInferModel _ -> false
 
-let exists_cache = Hashtbl.create 256
+let exists_cache = String.Table.create ~size:256 ()
 
 let path_exists abs_path =
-  try Hashtbl.find exists_cache abs_path
+  try String.Table.find_exn exists_cache abs_path
   with Not_found ->
-    let result = Sys.file_exists  abs_path in
-    Hashtbl.add exists_cache abs_path result;
+    let result = Sys.file_exists abs_path in
+    String.Table.set exists_cache ~key:abs_path ~data:result;
     result
 
 let of_header header_file =
@@ -133,7 +134,7 @@ let of_header header_file =
   let header_exts = ["h"; "hh"; "hpp"; "hxx"] in
   let file_no_ext, ext_opt = Core.Std.Filename.split_extension abs_path in
   let file_opt = match ext_opt with
-    | Some ext when IList.mem Core.Std.String.equal ext header_exts -> (
+    | Some ext when IList.mem String.equal ext header_exts -> (
         let possible_files = IList.map (fun ext -> file_no_ext ^ "." ^ ext) source_exts in
         try Some (IList.find path_exists possible_files)
         with Not_found -> None
diff --git a/infer/src/base/Utils.ml b/infer/src/base/Utils.ml
index 41a78d2ff..b8cb76d2e 100644
--- a/infer/src/base/Utils.ml
+++ b/infer/src/base/Utils.ml
@@ -11,6 +11,7 @@
 (** General utility functions and definition with global scope *)
 
 module Int = Core.Std.Int
+module String = Core.Std.String
 
 module F = Format
 
@@ -45,7 +46,7 @@ let int_of_bool b = if b then 1 else 0
 module IntSet = Set.Make(Int)
 
 (** Hash table over strings *)
-module StringHash = Hashtbl.Make (Core.Std.String)
+module StringHash = Hashtbl.Make (String)
 
 (** Set of strings *)
 module StringSet = Set.Make(String)
@@ -65,7 +66,7 @@ let string_list_intersection a b =
   StringSet.inter (string_set_of_list a) (string_set_of_list b)
 
 module StringPPSet = PrettyPrintable.MakePPSet(struct
-    include Core.Std.String
+    include String
     let pp_element fmt s = F.fprintf fmt "%s" s
   end)
 
@@ -73,7 +74,7 @@ module StringPPSet = PrettyPrintable.MakePPSet(struct
 module IntMap = Map.Make (Int)
 
 (** Maps from strings *)
-module StringMap = Map.Make (Core.Std.String)
+module StringMap = Map.Make (String)
 
 (** {2 Printing} *)
 
@@ -225,35 +226,6 @@ let pp_elapsed_time fmt () =
   let elapsed = Unix.gettimeofday () -. initial_timeofday in
   Format.fprintf fmt "%f" elapsed
 
-(** Check if the lhs is a substring of the rhs. *)
-let string_is_prefix s1 s2 =
-  String.length s1 <= String.length s2 &&
-  String.sub s2 0 (String.length s1) = s1
-
-(** Check if the lhs is a postfix of the rhs. *)
-let string_is_suffix s1 s2 =
-  let l1 = String.length s1 in
-  let l2 = String.length s2 in
-  l1 <= l2 &&
-  String.sub s2 (l2 - l1) l1 = s1
-
-(** Check if the lhs is contained in the rhs. *)
-let string_contains s1 s2 =
-  let rexp = Str.regexp_string s1 in
-  try
-    ignore (Str.search_forward rexp s2 0);
-    true
-  with Not_found -> false
-
-(** Split a string across the given character, if given. (e.g. split first.second with '.').*)
-let string_split_character s c =
-  try
-    let index = String.rindex s c in
-    let lhs = String.sub s 0 index in
-    let rhs = String.sub s (index + 1) ((String.length s) - (1 + index)) in
-    (Some lhs, rhs)
-  with Not_found -> (None, s)
-
 let string_value_or_empty_string
     (string_option: string option): string =
   match string_option with
@@ -429,8 +401,8 @@ let filename_to_absolute fname =
 let filename_to_relative root fname =
   let string_strict_subtract s1 s2 =
     let n1, n2 = String.length s1, String.length s2 in
-    if n1 < n2 && String.sub s2 0 n1 = s1 then
-      String.sub s2 (n1 + 1) (n2 - (n1 + 1))
+    if n1 < n2 && String.sub s2 ~pos:0 ~len:n1 = s1 then
+      String.sub s2 ~pos:(n1 + 1) ~len:(n2 - (n1 + 1))
     else s2 in
   let norm_root = (* norm_root is root without any trailing / *)
     Filename.dirname root // Filename.basename root in
@@ -458,11 +430,6 @@ let proc_flags_add proc_flags key value =
 let proc_flags_find proc_flags key =
   Hashtbl.find proc_flags key
 
-let join_strings sep = function
-  | [] -> ""
-  | hd:: tl ->
-      IList.fold_left (fun str p -> str ^ sep ^ p) hd tl
-
 
 let directory_fold f init path =
   let collect current_dir (accu, dirs) path =
@@ -524,7 +491,7 @@ let string_append_crc_cutoff ?(cutoff=100) ?(key="") name =
   let name_up_to_cutoff =
     if String.length name <= cutoff
     then name
-    else String.sub name 0 cutoff in
+    else String.sub name ~pos:0 ~len:cutoff in
   let crc_str =
     let name_for_crc = name ^ key in
     string_crc_hex32 name_for_crc in
diff --git a/infer/src/base/Utils.mli b/infer/src/base/Utils.mli
index a677d4025..b16f94b06 100644
--- a/infer/src/base/Utils.mli
+++ b/infer/src/base/Utils.mli
@@ -11,6 +11,7 @@
 (** General utility functions *)
 
 module Int = Core.Std.Int
+module String = Core.Std.String
 
 (** {2 Generic Utility Functions} *)
 
@@ -156,18 +157,6 @@ val string_crc_hex32 : string -> string
     Use an optional key to compute the crc.  *)
 val string_append_crc_cutoff : ?cutoff:int -> ?key:string -> string -> string
 
-(** Check if the lhs is a substring of the rhs. *)
-val string_is_prefix : string -> string -> bool
-
-(** Check if the lhs is a suffix of the rhs. *)
-val string_is_suffix : string -> string -> bool
-
-(** Check if the lhs is contained in the rhs. *)
-val string_contains : string -> string -> bool
-
-(** Split a string across the given character, if given. (e.g. split first.second with '.').*)
-val string_split_character : string -> char -> string option * string
-
 (** The value of a string option or the empty string.: *)
 val string_value_or_empty_string : string option -> string
 
@@ -219,9 +208,6 @@ val proc_flags_add : proc_flags -> string -> string -> unit
 (** find a value for a key in the proc flags *)
 val proc_flags_find : proc_flags -> string -> string
 
-(** [join_strings sep parts] contatenates the elements of [parts] using [sep] as separator *)
-val join_strings : string -> string list -> string
-
 (** Functional fold function over all the file of a directory *)
 val directory_fold : ('a -> string -> 'a) -> 'a -> string -> 'a
 
diff --git a/infer/src/base/Version.ml.in b/infer/src/base/Version.ml.in
index 50a77ecc8..3b5d7a973 100644
--- a/infer/src/base/Version.ml.in
+++ b/infer/src/base/Version.ml.in
@@ -16,14 +16,14 @@ let patch = @INFER_PATCH@
 
 let commit = "@INFER_GIT_COMMIT@"
 let branch = "@INFER_GIT_BRANCH@"
-let is_release = Core.Std.String.equal "@IS_RELEASE_TREE@" "yes"
+let is_release = String.equal "@IS_RELEASE_TREE@" "yes"
 let tag = Printf.sprintf "v%d.%d.%d" major minor patch
 
 let versionString =
   if is_release then tag
   else Printf.sprintf "%s-%s" tag commit
 
-let versionJson = String.concat "\n" [
+let versionJson = String.concat ~sep:"\n" [
     "{"; "\"major\": " ^ (string_of_int major) ^ ", ";
     "\"minor\": " ^ (string_of_int minor) ^ ", ";
     "\"patch\": " ^ (string_of_int patch) ^ ", ";
diff --git a/infer/src/checkers/BoundedCallTree.ml b/infer/src/checkers/BoundedCallTree.ml
index 5318525bd..d1094c885 100644
--- a/infer/src/checkers/BoundedCallTree.ml
+++ b/infer/src/checkers/BoundedCallTree.ml
@@ -114,11 +114,11 @@ module TransferFunctions (CFG : ProcCfg.S) = struct
         let matches_proc frame =
           let matches_class pname = match pname with
             | Procname.Java java_proc ->
-                Core.Std.String.equal
+                String.equal
                   frame.Stacktrace.class_str
                   (Procname.java_get_class_name java_proc)
             | Procname.ObjC_Cpp objc_cpp_prod ->
-                Core.Std.String.equal
+                String.equal
                   frame.Stacktrace.class_str
                   (Procname.objc_cpp_get_class_name objc_cpp_prod)
             | Procname.C _ -> true (* Needed for test code. *)
diff --git a/infer/src/checkers/Siof.ml b/infer/src/checkers/Siof.ml
index 294debedd..247d85ec0 100644
--- a/infer/src/checkers/Siof.ml
+++ b/infer/src/checkers/Siof.ml
@@ -110,7 +110,7 @@ let is_foreign tu_opt v =
   let is_orig_file f = match tu_opt with
     | Some orig_file ->
         let orig_path = SourceFile.to_abs_path orig_file in
-        Core.Std.String.equal orig_path (SourceFile.to_abs_path f)
+        String.equal orig_path (SourceFile.to_abs_path f)
     | None -> assert false in
   Option.map_default (fun f -> not (is_orig_file f)) false (Pvar.get_source_file v)
 
diff --git a/infer/src/checkers/Stacktrace.ml b/infer/src/checkers/Stacktrace.ml
index e3823e161..73b4437db 100644
--- a/infer/src/checkers/Stacktrace.ml
+++ b/infer/src/checkers/Stacktrace.ml
@@ -44,7 +44,7 @@ let make_frame class_str method_str file_str line_num =
 
 let frame_matches_location frame_obj loc =
   let lfname = SourceFile.to_string loc.Location.file in
-  let matches_file = Utils.string_is_suffix frame_obj.file_str lfname in
+  let matches_file = String.is_suffix ~suffix:frame_obj.file_str lfname in
   let matches_line = match frame_obj.line_num with
     | None -> false
     | Some line -> line = loc.Location.line in
@@ -60,7 +60,7 @@ let parse_stack_frame frame_str =
   let class_str = Str.matched_group 1 qualified_procname in
   let method_str = Str.matched_group 2 qualified_procname in
   (* Native methods don't have debugging info *)
-  if Core.Std.String.equal file_and_line "Native Method" then
+  if String.equal file_and_line "Native Method" then
     make_frame class_str method_str "Native Method" None
   else begin
     (* Separate the filename and line number.
@@ -100,7 +100,7 @@ let of_json filename json =
   let frames =
     Yojson.Basic.Util.to_list (extract_json_member frames_key)
     |> IList.map Yojson.Basic.Util.to_string
-    |> IList.map String.trim
+    |> IList.map String.strip
     |> IList.filter (fun s -> s <> "")
     |> IList.map parse_stack_frame in
   make exception_name frames
diff --git a/infer/src/checkers/ThreadSafety.ml b/infer/src/checkers/ThreadSafety.ml
index 51ba8996e..3c7a8b254 100644
--- a/infer/src/checkers/ThreadSafety.ml
+++ b/infer/src/checkers/ThreadSafety.ml
@@ -28,7 +28,7 @@ module Summary = Summary.Make (struct
    is assumed to be thread-safe. in the future, we can ask for builder classes to be annotated with
    @Builder and verify that annotated classes satisfy the expected invariants. *)
 let is_builder_class class_name =
-  string_is_suffix "Builder" class_name
+  String.is_suffix ~suffix:"Builder" class_name
 
 let is_call_to_builder_class_method = function
   | Procname.Java java_pname -> is_builder_class (Procname.java_get_class_name java_pname)
diff --git a/infer/src/checkers/annotations.ml b/infer/src/checkers/annotations.ml
index f8b015813..3b2983596 100644
--- a/infer/src/checkers/annotations.ml
+++ b/infer/src/checkers/annotations.ml
@@ -53,7 +53,7 @@ let annot_ends_with annot ann_name =
   let filter s =
     let sl = String.length s in
     let al = String.length ann_name in
-    sl >= al && String.sub s (sl - al) al = ann_name in
+    sl >= al && String.sub s ~pos:(sl - al) ~len:al = ann_name in
   filter annot.Annot.class_name
 
 (** Check if there is an annotation in [ia] which ends with the given name *)
@@ -75,7 +75,7 @@ let ia_get ia ann_name =
 let ma_contains ma ann_names =
   let found = ref false in
   ma_iter (fun a ->
-      if IList.exists (Core.Std.String.equal a.Annot.class_name) ann_names then found := true
+      if IList.exists (String.equal a.Annot.class_name) ann_names then found := true
     ) ma;
   !found
 
@@ -254,8 +254,8 @@ let annotated_signature_is_anonymous_inner_class_wrapper ann_sig proc_name =
     let name_str = Mangled.to_string name in
     let len = String.length name_str in
     len >= 2 &&
-    String.sub name_str 0 1 = "x" &&
-    let s = String.sub name_str 1 (len - 1) in
+    String.sub name_str ~pos:0 ~len:1 = "x" &&
+    let s = String.sub name_str ~pos:1 ~len:(len - 1) in
     let is_int =
       try
         ignore (int_of_string s);
diff --git a/infer/src/checkers/checkTraceCallSequence.ml b/infer/src/checkers/checkTraceCallSequence.ml
index ba7a15477..bde3d8abc 100644
--- a/infer/src/checkers/checkTraceCallSequence.ml
+++ b/infer/src/checkers/checkTraceCallSequence.ml
@@ -230,7 +230,7 @@ module BooleanVars = struct
   let exp_boolean_var exp = match exp with
     | Exp.Lvar pvar when Pvar.is_local pvar ->
         let name = Mangled.to_string (Pvar.get_name pvar) in
-        if IList.mem Core.Std.String.equal name boolean_variables
+        if IList.mem String.equal name boolean_variables
         then Some name
         else None
     | _ -> None
diff --git a/infer/src/checkers/checkers.ml b/infer/src/checkers/checkers.ml
index d2bd7f7c2..4f669e9c6 100644
--- a/infer/src/checkers/checkers.ml
+++ b/infer/src/checkers/checkers.ml
@@ -95,13 +95,13 @@ module ST = struct
         let drop_prefix str =
           Str.replace_first (Str.regexp "^[A-Za-z]+_") "" str in
         let normalized_equal s1 s2 =
-          Core.Std.String.equal (normalize s1) (normalize s2) in
+          String.equal (normalize s1) (normalize s2) in
 
         let is_parameter_suppressed =
-          IList.mem Core.Std.String.equal a.class_name [Annotations.suppressLint] &&
+          IList.mem String.equal a.class_name [Annotations.suppressLint] &&
           IList.mem normalized_equal kind a.parameters in
         let is_annotation_suppressed =
-          string_is_suffix (normalize (drop_prefix kind)) (normalize a.class_name) in
+          String.is_suffix ~suffix:(normalize (drop_prefix kind)) (normalize a.class_name) in
 
         is_parameter_suppressed || is_annotation_suppressed in
 
@@ -235,9 +235,9 @@ let callback_check_write_to_parcel_java
           let method_name = Procname.java_get_method pname_java in
           (try
              class_name = "android.os.Parcel" &&
-             (String.sub method_name 0 5 = "write"
+             (String.sub method_name ~pos:0 ~len:5 = "write"
               ||
-              String.sub method_name 0 4 = "read")
+              String.sub method_name ~pos:0 ~len:4 = "read")
            with Invalid_argument _ -> false)
       | _ -> assert false in
 
@@ -247,8 +247,8 @@ let callback_check_write_to_parcel_java
           let wn = Procname.java_get_method wc in
           let postfix_length = String.length wn - 5 in (* covers writeList <-> readArrayList etc. *)
           (try
-             String.sub rn (String.length rn - postfix_length) postfix_length =
-             String.sub wn 5 postfix_length
+             String.sub rn ~pos:(String.length rn - postfix_length) ~len:postfix_length =
+             String.sub wn ~pos:5 ~len:postfix_length
            with Invalid_argument _ -> false)
       | _ ->
           false in
diff --git a/infer/src/checkers/immutableChecker.ml b/infer/src/checkers/immutableChecker.ml
index 38630f37b..0cec4b466 100644
--- a/infer/src/checkers/immutableChecker.ml
+++ b/infer/src/checkers/immutableChecker.ml
@@ -25,8 +25,8 @@ let check_immutable_cast tenv curr_pname curr_pdesc typ_expected typ_found_opt l
           ] in
         let in_casts expected given =
           IList.exists (fun (x, y) ->
-              Core.Std.String.equal (Typename.name expected) x
-              && Core.Std.String.equal (Typename.name given) y
+              String.equal (Typename.name expected) x
+              && String.equal (Typename.name given) y
             ) casts in
         match PatternMatch.type_get_class_name typ_expected,
               PatternMatch.type_get_class_name typ_found with
diff --git a/infer/src/checkers/patternMatch.ml b/infer/src/checkers/patternMatch.ml
index 60c32994d..e260f3bc0 100644
--- a/infer/src/checkers/patternMatch.ml
+++ b/infer/src/checkers/patternMatch.ml
@@ -107,7 +107,7 @@ let type_has_supertype
   has_supertype typ Typ.Set.empty
 
 let type_is_nested_in_direct_supertype tenv t n =
-  let is_nested_in cn1 cn2 = string_is_prefix (Typename.name cn1 ^ "$") (Typename.name cn2) in
+  let is_nested_in cn1 cn2 = String.is_prefix ~prefix:(Typename.name cn1 ^ "$") (Typename.name cn2) in
   IList.exists (is_nested_in n) (type_get_direct_supertypes tenv t)
 
 let rec get_type_name = function
@@ -273,7 +273,7 @@ let method_is_initializer
         match proc_attributes.ProcAttributes.proc_name with
         | Procname.Java pname_java ->
             let mname = Procname.java_get_method pname_java in
-            IList.exists (Core.Std.String.equal mname) initializer_methods
+            IList.exists (String.equal mname) initializer_methods
         | _ ->
             false
       else
diff --git a/infer/src/checkers/printfArgs.ml b/infer/src/checkers/printfArgs.ml
index 581f0153f..44b1d3d7f 100644
--- a/infer/src/checkers/printfArgs.ml
+++ b/infer/src/checkers/printfArgs.ml
@@ -49,7 +49,7 @@ let printf_like_function
   try
     Some (
       IList.find
-        (fun printf -> Core.Std.String.equal printf.unique_id (Procname.to_unique_id proc_name))
+        (fun printf -> String.equal printf.unique_id (Procname.to_unique_id proc_name))
         !printf_like_functions)
   with Not_found -> None
 
@@ -70,15 +70,15 @@ let format_type_matches_given_type
   match format_type with
   | "d" | "i" | "u" | "x" | "X" | "o" ->
       IList.mem
-        Core.Std.String.equal
+        String.equal
         given_type
         ["java.lang.Integer"; "java.lang.Long"; "java.lang.Short"; "java.lang.Byte"]
   | "a" | "A" | "f" | "F" | "g" | "G" | "e" | "E" ->
       IList.mem
-        Core.Std.String.equal
+        String.equal
         given_type
         ["java.lang.Double"; "java.lang.Float"]
-  | "c" -> Core.Std.String.equal given_type "java.lang.Character"
+  | "c" -> String.equal given_type "java.lang.Character"
   | "b" | "h" | "H" | "s" -> true  (* accepts pretty much anything, even null *)
   | _ -> false
 
@@ -108,7 +108,7 @@ let rec format_string_type_names
     let fmt_re = Str.regexp "%[0-9]*\\.?[0-9]*[A-mo-z]" in (* matches '%2.1d' etc. *)
     let _ = Str.search_forward fmt_re fmt_string start in
     let fmt_match = Str.matched_string fmt_string in
-    let fmt_type = String.sub fmt_match ((String.length fmt_match) - 1) 1 in
+    let fmt_type = String.sub fmt_match ~pos:((String.length fmt_match) - 1) ~len:1 in
     fmt_type:: format_string_type_names fmt_string (Str.match_end ())
   with Not_found -> []
 
@@ -221,6 +221,6 @@ let printf_signature_to_string
     "{%s; %d [%s] %s}"
     printf.unique_id
     printf.format_pos
-    (String.concat "," (IList.map string_of_int printf.fixed_pos))
+    (String.concat ~sep:"," (IList.map string_of_int printf.fixed_pos))
     (match printf.vararg_pos with | Some i -> string_of_int i | _ -> "-")
 *)
diff --git a/infer/src/clang/CType.ml b/infer/src/clang/CType.ml
index 7593610a6..c158f9b10 100644
--- a/infer/src/clang/CType.ml
+++ b/infer/src/clang/CType.ml
@@ -38,7 +38,7 @@ let mk_structname n = Typename.TN_csu (Csu.Struct, Mangled.from_string n)
 let is_class typ =
   match typ with
   | Typ.Tptr (Tstruct ((TN_csu _) as name), _) ->
-      Core.Std.String.equal (Typename.name name) CFrontend_config.objc_class
+      String.equal (Typename.name name) CFrontend_config.objc_class
   | _ -> false
 
 let rec return_type_of_function_type_ptr type_ptr =
diff --git a/infer/src/clang/CType_decl.ml b/infer/src/clang/CType_decl.ml
index f99768153..799b8bc12 100644
--- a/infer/src/clang/CType_decl.ml
+++ b/infer/src/clang/CType_decl.ml
@@ -120,7 +120,7 @@ let get_superclass_list_cpp decl =
 let get_translate_as_friend_decl decl_list =
   let is_translate_as_friend_name (_, name_info) =
     let translate_as_str = "infer_traits::TranslateAsType" in
-    string_contains translate_as_str (Ast_utils.get_qualified_name name_info) in
+    String.is_substring ~substring:translate_as_str (Ast_utils.get_qualified_name name_info) in
   let get_friend_decl_opt (decl : Clang_ast_t.decl) = match decl with
     | FriendDecl (_, `Type type_ptr) -> Ast_utils.get_decl_from_typ_ptr type_ptr
     | _ -> None in
diff --git a/infer/src/clang/Capture.re b/infer/src/clang/Capture.re
index 7dac77fcd..2eae2a26b 100644
--- a/infer/src/clang/Capture.re
+++ b/infer/src/clang/Capture.re
@@ -141,7 +141,7 @@ let run_plugin_and_frontend source_path frontend clang_args => {
     Format.fprintf debug_script_fmt "%s \\@\n  > %s@\n" clang_command biniou_fname;
     let infer_clang_options =
       String.concat
-        "^"
+        sep::"^"
         (
           (
             try [Unix.getenv CLOpt.args_env_var] {
diff --git a/infer/src/clang/ClangCommand.re b/infer/src/clang/ClangCommand.re
index 7f134011c..55ca8db2e 100644
--- a/infer/src/clang/ClangCommand.re
+++ b/infer/src/clang/ClangCommand.re
@@ -37,7 +37,7 @@ let value_of_argv_option argv opt_name =>
         let result' =
           if (Option.is_some result) {
             result
-          } else if (Core.Std.String.equal opt_name prev_arg) {
+          } else if (String.equal opt_name prev_arg) {
             Some arg
           } else {
             None
@@ -50,7 +50,7 @@ let value_of_argv_option argv opt_name =>
 
 let value_of_option {orig_argv} => value_of_argv_option orig_argv;
 
-let has_flag {orig_argv} flag => IList.exists (Core.Std.String.equal flag) orig_argv;
+let has_flag {orig_argv} flag => IList.exists (String.equal flag) orig_argv;
 
 let can_attach_ast_exporter cmd =>
   has_flag cmd "-cc1" && (
@@ -58,7 +58,7 @@ let can_attach_ast_exporter cmd =>
     | None =>
       Logging.stderr "malformed -cc1 command has no \"-x\" flag!";
       false
-    | Some lang when string_is_prefix "assembler" lang => false
+    | Some lang when String.is_prefix prefix::"assembler" lang => false
     | Some _ => true
     }
   );
@@ -84,14 +84,14 @@ let clang_cc1_cmd_sanitizer cmd => {
   /* command line options not supported by the opensource compiler or the plugins */
   let flags_blacklist = ["-fembed-bitcode-marker", "-fno-canonical-system-headers"];
   let replace_option_arg option arg =>
-    if (Core.Std.String.equal option "-arch" && Core.Std.String.equal arg "armv7k") {
+    if (String.equal option "-arch" && String.equal arg "armv7k") {
       "armv7"
       /* replace armv7k arch with armv7 */
     } else if (
-      Core.Std.String.equal option "-isystem"
+      String.equal option "-isystem"
     ) {
       switch Config.clang_include_to_override {
-      | Some to_replace when Core.Std.String.equal arg to_replace =>
+      | Some to_replace when String.equal arg to_replace =>
         fcp_dir /\/ "clang" /\/ "install" /\/ "lib" /\/ "clang" /\/ "4.0.0" /\/ "include"
       | _ => arg
       }
@@ -110,7 +110,7 @@ let clang_cc1_cmd_sanitizer cmd => {
     | [] =>
       /* return non-reversed list */
       IList.rev (post_args_rev @ res_rev)
-    | [flag, ...tl] when IList.mem Core.Std.String.equal flag flags_blacklist =>
+    | [flag, ...tl] when IList.mem String.equal flag flags_blacklist =>
       filter_unsupported_args_and_swap_includes (flag, res_rev) tl
     | [arg, ...tl] => {
         let res_rev' = [replace_option_arg prev arg, ...res_rev];
@@ -132,12 +132,12 @@ let command_to_run cmd => {
   let mk_cmd normalizer => {
     let {exec, argv, quoting_style} = normalizer cmd;
     Printf.sprintf
-      "'%s' %s" exec (IList.map (ClangQuotes.quote quoting_style) argv |> String.concat " ")
+      "'%s' %s" exec (IList.map (ClangQuotes.quote quoting_style) argv |> String.concat sep::" ")
   };
   if (can_attach_ast_exporter cmd) {
     mk_cmd clang_cc1_cmd_sanitizer
   } else if (
-    string_is_prefix "clang" (Filename.basename cmd.exec)
+    String.is_prefix prefix::"clang" (Filename.basename cmd.exec)
   ) {
     /* `clang` supports argument files and the commands can be longer than the maximum length of the
        command line, so put arguments in a file */
diff --git a/infer/src/clang/ClangWrapper.re b/infer/src/clang/ClangWrapper.re
index a5364049f..1f25e9382 100644
--- a/infer/src/clang/ClangWrapper.re
+++ b/infer/src/clang/ClangWrapper.re
@@ -37,7 +37,7 @@ let normalize (args: array string) :list action_item => {
   Logging.out "clang -### invocation: %s@\n" clang_hashhashhash;
   let normalized_commands = ref [];
   let one_line line =>
-    if (string_is_prefix " \"" line) {
+    if (String.is_prefix prefix::" \"" line) {
       let cmd =
         /* massage line to remove edge-cases for splitting */
         "\"" ^ line ^ " \"" |>
@@ -112,7 +112,7 @@ let exe args xx_suffix => {
            files. */
       Logging.out
         "WARNING: `clang -### <args>` returned an empty set of commands to run and no error. Will run the original command directly:@\n  %s@\n"
-        (String.concat " " @@ Array.to_list args)
+        (String.concat sep::" " @@ Array.to_list args)
     };
     Process.create_process_and_wait args
   }
diff --git a/infer/src/clang/ComponentKit.ml b/infer/src/clang/ComponentKit.ml
index 8bc8e2c17..8aadf5922 100644
--- a/infer/src/clang/ComponentKit.ml
+++ b/infer/src/clang/ComponentKit.ml
@@ -97,9 +97,9 @@ let mutable_local_vars_advice context an =
     let objc_whitelist = ["NSError"] in
     match get_referenced_type qual_type with
     | Some CXXRecordDecl (_, ndi, _, _, _, _, _, _) ->
-        IList.mem Core.Std.String.equal ndi.ni_name cpp_whitelist
+        IList.mem String.equal ndi.ni_name cpp_whitelist
     | Some ObjCInterfaceDecl (_, ndi, _, _, _) ->
-        IList.mem Core.Std.String.equal ndi.ni_name objc_whitelist
+        IList.mem String.equal ndi.ni_name objc_whitelist
     | _ -> false in
 
   match an with
@@ -168,7 +168,7 @@ let component_with_unconventional_superclass_advice context an =
           let has_conventional_superclass =
             let open CFrontend_config in
             match superclass_name with
-            | Some name when IList.mem Core.Std.String.equal name [
+            | Some name when IList.mem String.equal name [
                 ckcomponent_cl;
                 ckcomponentcontroller_cl;
                 "CKCompositeComponent";
diff --git a/infer/src/clang/InferClang.re b/infer/src/clang/InferClang.re
index 144e122e0..03e936c8d 100644
--- a/infer/src/clang/InferClang.re
+++ b/infer/src/clang/InferClang.re
@@ -9,7 +9,7 @@
 open! Utils;
 
 let () = {
-  let xx_suffix = string_is_suffix "++" Sys.argv.(0) ? "++" : "";
+  let xx_suffix = String.is_suffix suffix::"++" Sys.argv.(0) ? "++" : "";
   let args = Array.copy Sys.argv;
   ClangWrapper.exe args xx_suffix
 };
diff --git a/infer/src/clang/cFrontend_utils.ml b/infer/src/clang/cFrontend_utils.ml
index 108c4a719..04a97c977 100644
--- a/infer/src/clang/cFrontend_utils.ml
+++ b/infer/src/clang/cFrontend_utils.ml
@@ -419,7 +419,7 @@ struct
       match if_decl with
       | Some Clang_ast_t.ObjCInterfaceDecl (_, ndi, _, _, _) ->
           let in_list some_list =
-            IList.mem Core.Std.String.equal ndi.Clang_ast_t.ni_name some_list in
+            IList.mem String.equal ndi.Clang_ast_t.ni_name some_list in
           not (in_list blacklist)
           && (in_list ancestors
               || is_objc_if_descendant ~blacklist:blacklist (get_super_if if_decl) ancestors)
diff --git a/infer/src/clang/cLocation.ml b/infer/src/clang/cLocation.ml
index b06dc3cb3..aa278c358 100644
--- a/infer/src/clang/cLocation.ml
+++ b/infer/src/clang/cLocation.ml
@@ -23,7 +23,7 @@ let source_file_in_project source_file =
   let rel_source_file = SourceFile.to_string source_file in
   let file_should_be_skipped =
     IList.exists
-      (fun path -> string_is_prefix path rel_source_file)
+      (fun path -> String.is_prefix ~prefix:path rel_source_file)
       Config.skip_translation_headers in
   file_in_project && not (file_should_be_skipped)
 
diff --git a/infer/src/clang/cTL.ml b/infer/src/clang/cTL.ml
index 590d8bc7f..19ca86922 100644
--- a/infer/src/clang/cTL.ml
+++ b/infer/src/clang/cTL.ml
@@ -288,7 +288,7 @@ let node_to_unique_string_id an =
 (* true iff an ast node is a node of type among the list tl *)
 let node_has_type tl an =
   let an_str = node_to_string an in
-  IList.mem Core.Std.String.equal an_str tl
+  IList.mem String.equal an_str tl
 
 (* given a decl returns a stmt such that decl--->stmt via label trs *)
 let transition_decl_to_stmt d trs =
@@ -467,7 +467,7 @@ and in_node node_type_list phi an lctx =
   let holds_for_one_node n =
     match lctx.CLintersContext.et_evaluation_node with
     | Some id ->
-        (Core.Std.String.equal id (node_to_unique_string_id an)) && (eval_formula phi an lctx)
+        (String.equal id (node_to_unique_string_id an)) && (eval_formula phi an lctx)
     | None ->
         (node_has_type [n] an) && (eval_formula phi an lctx) in
   IList.exists holds_for_one_node node_type_list
diff --git a/infer/src/clang/cTrans_models.ml b/infer/src/clang/cTrans_models.ml
index 2c73ff109..a5702b5b3 100644
--- a/infer/src/clang/cTrans_models.ml
+++ b/infer/src/clang/cTrans_models.ml
@@ -67,7 +67,7 @@ let is_modeled_builtin funct =
   funct = CFrontend_config.builtin_memset_chk
 
 let is_modeled_attribute attr_name =
-  IList.mem Core.Std.String.equal attr_name CFrontend_config.modeled_function_attributes
+  IList.mem String.equal attr_name CFrontend_config.modeled_function_attributes
 
 let get_first_param_typedef_string_opt type_ptr =
   match Ast_utils.get_desugared_type type_ptr with
@@ -93,7 +93,7 @@ let is_assert_log_s funct =
   funct = CFrontend_config.assert_rtn ||
   funct = CFrontend_config.assert_fail ||
   funct = CFrontend_config.fbAssertWithSignalAndLogFunctionHelper ||
-  Utils.string_contains CFrontend_config.google_MakeCheckOpString funct
+  String.is_substring ~substring:CFrontend_config.google_MakeCheckOpString funct
 
 let is_assert_log_method m =
   m = CFrontend_config.google_LogMessageFatal
diff --git a/infer/src/eradicate/eradicate.ml b/infer/src/eradicate/eradicate.ml
index c28191952..7048df904 100644
--- a/infer/src/eradicate/eradicate.ml
+++ b/infer/src/eradicate/eradicate.ml
@@ -88,7 +88,7 @@ struct
         | Some (typ_found, _, _) -> Some typ_found
         | None -> None in
       let ret_implicitly_nullable =
-        Core.Std.String.equal (PatternMatch.get_type_name ret_type) "java.lang.Void" in
+        String.equal (PatternMatch.get_type_name ret_type) "java.lang.Void" in
       State.set_node exit_node;
 
       if checks.TypeCheck.check_ret_type <> [] then
diff --git a/infer/src/eradicate/eradicateChecks.ml b/infer/src/eradicate/eradicateChecks.ml
index 782d716de..38ab10c5c 100644
--- a/infer/src/eradicate/eradicateChecks.ml
+++ b/infer/src/eradicate/eradicateChecks.ml
@@ -50,7 +50,7 @@ let classify_procedure proc_attributes =
     if Models.is_modelled_nullable pn then "M" (* modelled *)
     else if Specs.proc_is_library proc_attributes then "L" (* library *)
     else if not proc_attributes.ProcAttributes.is_defined then "S" (* skip *)
-    else if string_is_prefix "com.facebook" unique_id then "F" (* FB *)
+    else if String.is_prefix ~prefix:"com.facebook" unique_id then "F" (* FB *)
     else "?" in
   classification
 
@@ -116,7 +116,7 @@ let check_condition tenv case_zero find_canonical_duplicate curr_pdesc
     let throwable_found = ref false in
     let typ_is_throwable = function
       | Typ.Tstruct (TN_csu (Class Java, _) as name) ->
-          Core.Std.String.equal (Typename.name name) "java.lang.Throwable"
+          String.equal (Typename.name name) "java.lang.Throwable"
       | _ -> false in
     let do_instr = function
       | Sil.Call (_, Exp.Const (Const.Cfun pn), [_; (Exp.Sizeof(t, _, _), _)], _, _) when
@@ -133,8 +133,8 @@ let check_condition tenv case_zero find_canonical_duplicate curr_pdesc
     (* heuristic to check if the condition is the translation of try-with-resources *)
     match Printer.LineReader.from_loc linereader loc with
     | Some line ->
-        not (string_contains "==" line || string_contains "!=" line)
-        && (string_contains "}" line)
+        not (String.is_substring ~substring:"==" line || String.is_substring ~substring:"!=" line)
+        && (String.is_substring ~substring:"}" line)
         && contains_instanceof_throwable curr_pdesc node
     | None -> false in
 
@@ -273,7 +273,7 @@ let check_constructor_initialization tenv
               let should_check_field_initialization =
                 let in_current_class =
                   let fld_cname = Ident.java_fieldname_get_class fn in
-                  Core.Std.String.equal (Typename.name name) fld_cname in
+                  String.equal (Typename.name name) fld_cname in
                 not injector_readonly_annotated &&
                 PatternMatch.type_is_class ft &&
                 in_current_class &&
diff --git a/infer/src/eradicate/typeCheck.ml b/infer/src/eradicate/typeCheck.ml
index f3293e5ed..a0919e389 100644
--- a/infer/src/eradicate/typeCheck.ml
+++ b/infer/src/eradicate/typeCheck.ml
@@ -250,7 +250,7 @@ let typecheck_instr
   let handle_field_access_via_temporary typestate exp =
     let name_is_temporary name =
       let prefix = "$T" in
-      string_is_prefix prefix name in
+      String.is_prefix ~prefix:prefix name in
     let pvar_get_origin pvar =
       match TypeState.lookup_pvar pvar typestate with
       | Some (_, ta, _) ->
diff --git a/infer/src/harness/androidFramework.ml b/infer/src/harness/androidFramework.ml
index e2486c066..80c12e40d 100644
--- a/infer/src/harness/androidFramework.ml
+++ b/infer/src/harness/androidFramework.ml
@@ -22,8 +22,8 @@ let is_destroy_method pname =
   match pname with
   | Procname.Java pname_java ->
       let method_name = Procname.java_get_method pname_java in
-      Core.Std.String.equal method_name on_destroy
-      || Core.Std.String.equal method_name on_destroy_view
+      String.equal method_name on_destroy
+      || String.equal method_name on_destroy_view
   | _ ->
       false
 
@@ -79,7 +79,7 @@ let is_fragment tenv tname =
 (** return true if [class_name] is the name of a class that belong to the Android framework *)
 let is_android_lib_class class_name =
   let class_str = Typename.name class_name in
-  string_is_prefix "android" class_str || string_is_prefix "com.android" class_str
+  String.is_prefix ~prefix:"android" class_str || String.is_prefix ~prefix:"com.android" class_str
 
 (** given an Android framework type mangled string [lifecycle_typ] (e.g., android.app.Activity) and
     a list of method names [lifecycle_procs_strs], get the appropriate typ and procnames *)
diff --git a/infer/src/integration/CaptureCompilationDatabase.ml b/infer/src/integration/CaptureCompilationDatabase.ml
index 5f1a72981..15c424066 100644
--- a/infer/src/integration/CaptureCompilationDatabase.ml
+++ b/infer/src/integration/CaptureCompilationDatabase.ml
@@ -29,8 +29,8 @@ let should_capture_file_from_index () =
 
 (** The buck targets are assumed to start with //, aliases are not supported. *)
 let check_args_for_targets args =
-  if not (IList.exists (Utils.string_is_prefix "//") args) then
-    let args_s = String.concat " " args in
+  if not (IList.exists (String.is_prefix ~prefix:"//") args) then
+    let args_s = String.concat ~sep:" " args in
     Process.print_error_and_exit
       "Error reading buck command %s. Please, pass buck targets, aliases are not allowed.\n%!"
       args_s
@@ -43,7 +43,7 @@ let add_flavor_to_targets args =
     | _ -> assert false (* cannot happen *) in
   let process_arg arg =
     (* Targets are assumed to start with //, aliases are not allowed *)
-    if Utils.string_is_prefix "//" arg then arg ^ flavor
+    if String.is_prefix ~prefix:"//" arg then arg ^ flavor
     else arg in
   IList.map process_arg args
 
@@ -58,7 +58,7 @@ let swap_command cmd =
   let plusplus = "++" in
   let clang = "clang" in
   let clangplusplus = "clang++" in
-  if Utils.string_is_suffix plusplus cmd then
+  if String.is_suffix ~suffix:plusplus cmd then
     Config.wrappers_dir // clangplusplus
   else
     Config.wrappers_dir // clang
@@ -75,8 +75,8 @@ let run_compilation_file compilation_database file =
       let env0 = Unix.environment () in
       let found = ref false in
       Array.iteri (fun i key_val ->
-          match string_split_character key_val '=' with
-          | Some var, args when Core.Std.String.equal var CLOpt.args_env_var ->
+          match String.rsplit2 key_val ~on:'=' with
+          | Some (var, args) when String.equal var CLOpt.args_env_var ->
               found := true ;
               env0.(i) <-
                 F.sprintf "%s=%s%c--fcp-syntax-only" CLOpt.args_env_var args CLOpt.env_var_sep
@@ -113,12 +113,12 @@ let get_compilation_database_files_buck () =
            (buck :: build :: "--config" :: "*//cxx.pch_enabled=false" :: args_with_flavor) in
        Process.create_process_and_wait buck_build;
        let buck_targets_list = buck :: "targets" :: "--show-output" :: args_with_flavor in
-       let buck_targets = String.concat " " buck_targets_list in
+       let buck_targets = String.concat ~sep:" " buck_targets_list in
        try
          match fst @@ Utils.with_process_in buck_targets Std.input_list with
          | [] -> Logging.stdout "There are no files to process, exiting."; exit 0
          | lines ->
-             Logging.out "Reading compilation database from:@\n%s@\n" (String.concat "\n" lines);
+             Logging.out "Reading compilation database from:@\n%s@\n" (String.concat ~sep:"\n" lines);
              let scan_output compilation_database_files chan =
                Scanf.sscanf chan "%s %s"
                  (fun target file -> StringMap.add target file compilation_database_files) in
@@ -130,7 +130,7 @@ let get_compilation_database_files_buck () =
            "Cannot execute %s\n%!"
            (buck_targets ^ " " ^ (Unix.error_message err)))
   | _ ->
-      let cmd = String.concat " " cmd in
+      let cmd = String.concat ~sep:" " cmd in
       Process.print_error_and_exit "Incorrect buck command: %s. Please use buck build <targets>" cmd
 
 (** Compute the compilation database files. *)
diff --git a/infer/src/integration/ClangQuotes.re b/infer/src/integration/ClangQuotes.re
index 7dbc00e2d..0befd29c9 100644
--- a/infer/src/integration/ClangQuotes.re
+++ b/infer/src/integration/ClangQuotes.re
@@ -34,7 +34,8 @@ let mk_arg_file prefix style args => {
   let temp_dir = Config.results_dir /\/ "clang";
   create_dir temp_dir;
   let file = Filename.temp_file temp_dir::temp_dir prefix ".txt";
-  let write_args outc => output_string outc (IList.map (quote style) args |> String.concat " ");
+  let write_args outc =>
+    output_string outc (IList.map (quote style) args |> String.concat sep::" ");
   with_file file f::write_args |> ignore;
   Logging.out "Clang options stored in file %s@\n" file;
   file
diff --git a/infer/src/java/jClasspath.ml b/infer/src/java/jClasspath.ml
index 6ea814a49..81c8a37b5 100644
--- a/infer/src/java/jClasspath.ml
+++ b/infer/src/java/jClasspath.ml
@@ -189,10 +189,7 @@ let load_from_verbose_output () =
 
 
 let classname_of_class_filename class_filename =
-  JBasics.make_cn
-    (String.map
-       (function | '/' -> '.' | c -> c)
-       class_filename)
+  JBasics.make_cn (String.map ~f:(function '/' -> '.' | c -> c) class_filename)
 
 
 let extract_classnames classnames jar_filename =
diff --git a/infer/src/java/jTrans.ml b/infer/src/java/jTrans.ml
index 49e2888dd..e998db67d 100644
--- a/infer/src/java/jTrans.ml
+++ b/infer/src/java/jTrans.ml
@@ -37,7 +37,8 @@ let fix_method_definition_line linereader proc_name loc =
     | _ -> assert false in
   let method_name =
     if Procname.is_constructor proc_name then
-      let inner_class_name cname = snd (string_split_character cname '$') in
+      let inner_class_name cname =
+        match String.rsplit2 cname ~on:'$' with Some (_, icn) -> icn | None -> cname in
       inner_class_name (Procname.java_get_simple_class_name proc_name_java)
     else Procname.java_get_method proc_name_java in
   let regex = Str.regexp (Str.quote method_name) in
diff --git a/infer/src/java/jTransType.ml b/infer/src/java/jTransType.ml
index 745bb1c11..af34f16d1 100644
--- a/infer/src/java/jTransType.ml
+++ b/infer/src/java/jTransType.ml
@@ -344,7 +344,7 @@ let get_class_type program tenv cn =
 
 (** return true if [field_name] is the autogenerated C.$assertionsDisabled field for class C *)
 let is_autogenerated_assert_field field_name =
-  Core.Std.String.equal (Ident.java_fieldname_get_field field_name) "$assertionsDisabled"
+  String.equal (Ident.java_fieldname_get_field field_name) "$assertionsDisabled"
 
 let is_closeable program tenv typ =
   let closeable_cn = JBasics.make_cn "java.io.Closeable" in
diff --git a/infer/src/unit/TaintTests.ml b/infer/src/unit/TaintTests.ml
index cb789f734..8f503f5f2 100644
--- a/infer/src/unit/TaintTests.ml
+++ b/infer/src/unit/TaintTests.ml
@@ -41,7 +41,7 @@ module MockTrace = Trace.Make(struct
       include MockTraceElem
 
       let get site =
-        if string_is_prefix "SOURCE" (Procname.to_string (CallSite.pname site))
+        if String.is_prefix ~prefix:"SOURCE" (Procname.to_string (CallSite.pname site))
         then Some site
         else None
 
@@ -54,7 +54,7 @@ module MockTrace = Trace.Make(struct
       include MockTraceElem
 
       let get site _ =
-        if string_is_prefix "SINK" (Procname.to_string (CallSite.pname site))
+        if String.is_prefix ~prefix:"SINK" (Procname.to_string (CallSite.pname site))
         then [Sink.make_sink_param site 0 ~report_reachable:false]
         else []
     end