diff --git a/src/lib_protocol_environment/sigs/v1/list.mli b/src/lib_protocol_environment/sigs/v1/list.mli
index 065d8db5f..1e37377d8 100644
--- a/src/lib_protocol_environment/sigs/v1/list.mli
+++ b/src/lib_protocol_environment/sigs/v1/list.mli
@@ -56,12 +56,6 @@ val tl : 'a list -> 'a list
 (** Return the given list without its first element. Raise
     [Failure "tl"] if the list is empty. *)
 
-val nth : 'a list -> int -> 'a
-(** Return the [n]-th element of the given list.
-    The first element (head of the list) is at position 0.
-    Raise [Failure "nth"] if the list is too short.
-    Raise [Invalid_argument "List.nth"] if [n] is negative. *)
-
 val nth_opt : 'a list -> int -> 'a option
 (** Return the [n]-th element of the given list.
     The first element (head of the list) is at position 0.
@@ -208,12 +202,6 @@ val memq : 'a -> 'a list -> bool
 (** {1 List searching} *)
 
 
-val find : ('a -> bool) -> 'a list -> 'a
-(** [find p l] returns the first element of the list [l]
-    that satisfies the predicate [p].
-    Raise [Not_found] if there is no value that satisfies [p] in the
-    list [l]. *)
-
 val find_opt: ('a -> bool) -> 'a list -> 'a option
 (** [find_opt p l] returns the first element of the list [l] that
     satisfies the predicate [p], or [None] if there is no value that
@@ -239,14 +227,6 @@ val partition : ('a -> bool) -> 'a list -> 'a list * 'a list
 (** {1 Association lists} *)
 
 
-val assoc : 'a -> ('a * 'b) list -> 'b
-(** [assoc a l] returns the value associated with key [a] in the list of
-    pairs [l]. That is,
-    [assoc a [ ...; (a,b); ...] = b]
-    if [(a,b)] is the leftmost binding of [a] in list [l].
-    Raise [Not_found] if there is no value associated with [a] in the
-    list [l]. *)
-
 val assoc_opt: 'a -> ('a * 'b) list -> 'b option
 (** [assoc_opt a l] returns the value associated with key [a] in the list of
     pairs [l]. That is,
@@ -256,10 +236,6 @@ val assoc_opt: 'a -> ('a * 'b) list -> 'b option
     list [l].
     @since 4.05 *)
 
-val assq : 'a -> ('a * 'b) list -> 'b
-(** Same as {!List.assoc}, but uses physical equality instead of structural
-    equality to compare keys. *)
-
 val assq_opt : 'a -> ('a * 'b) list -> 'b option
 (** Same as {!List.assoc_opt}, but uses physical equality instead of structural
     equality to compare keys.
diff --git a/src/lib_protocol_environment/sigs/v1/pervasives.mli b/src/lib_protocol_environment/sigs/v1/pervasives.mli
index b4b269651..ccf079c51 100644
--- a/src/lib_protocol_environment/sigs/v1/pervasives.mli
+++ b/src/lib_protocol_environment/sigs/v1/pervasives.mli
@@ -300,11 +300,6 @@ val string_of_bool : bool -> string
     may be shared, the user should not modify them directly.
 *)
 
-val bool_of_string : string -> bool
-(** Convert the given string to a boolean.
-    Raise [Invalid_argument "bool_of_string"] if the string is not
-    ["true"] or ["false"]. *)
-
 val bool_of_string_opt: string -> bool option
 (** Convert the given string to a boolean.
     Return [None] if the string is not
@@ -315,7 +310,7 @@ val bool_of_string_opt: string -> bool option
 val string_of_int : int -> string
 (** Return the string representation of an integer, in decimal. *)
 
-external int_of_string : string -> int = "caml_int_of_string"
+val int_of_string_opt: string -> int option
 (** Convert the given string to an integer.
     The string is read in decimal (by default, or if the string
     begins with [0u]), in hexadecimal (if it begins with [0x] or
@@ -329,13 +324,10 @@ external int_of_string : string -> int = "caml_int_of_string"
 
     The [_] (underscore) character can appear anywhere in the string
     and is ignored.
-    Raise [Failure "int_of_string"] if the given string is not
-    a valid representation of an integer, or if the integer represented
-    exceeds the range of integers representable in type [int]. *)
 
-
-val int_of_string_opt: string -> int option
-(** Same as [int_of_string], but returns [None] instead of raising.
+    Return [None] if the given string is not a valid representation of
+    an integer, or if the integer represented exceeds the range of
+    integers representable in type [int].
     @since 4.05
 *)
 
diff --git a/src/lib_protocol_environment/sigs/v1/string.mli b/src/lib_protocol_environment/sigs/v1/string.mli
index 075b72101..2113f9ffa 100644
--- a/src/lib_protocol_environment/sigs/v1/string.mli
+++ b/src/lib_protocol_environment/sigs/v1/string.mli
@@ -149,38 +149,18 @@ val escaped : string -> string
     i.e. [Scanf.unescaped (escaped s) = s] for any string [s] (unless
     [escape s] fails). *)
 
-val index : string -> char -> int
-(** [String.index s c] returns the index of the first
-    occurrence of character [c] in string [s].
-
-    Raise [Not_found] if [c] does not occur in [s]. *)
-
 val index_opt: string -> char -> int option
 (** [String.index_opt s c] returns the index of the first
     occurrence of character [c] in string [s], or
     [None] if [c] does not occur in [s].
     @since 4.05 *)
 
-val rindex : string -> char -> int
-(** [String.rindex s c] returns the index of the last
-    occurrence of character [c] in string [s].
-
-    Raise [Not_found] if [c] does not occur in [s]. *)
-
 val rindex_opt: string -> char -> int option
 (** [String.rindex_opt s c] returns the index of the last occurrence
     of character [c] in string [s], or [None] if [c] does not occur in
     [s].
     @since 4.05 *)
 
-val index_from : string -> int -> char -> int
-(** [String.index_from s i c] returns the index of the
-    first occurrence of character [c] in string [s] after position [i].
-    [String.index s c] is equivalent to [String.index_from s 0 c].
-
-    Raise [Invalid_argument] if [i] is not a valid position in [s].
-    Raise [Not_found] if [c] does not occur in [s] after position [i]. *)
-
 val index_from_opt: string -> int -> char -> int option
 (** [String.index_from_opt s i c] returns the index of the
     first occurrence of character [c] in string [s] after position [i]
@@ -192,15 +172,6 @@ val index_from_opt: string -> int -> char -> int option
     @since 4.05
 *)
 
-val rindex_from : string -> int -> char -> int
-(** [String.rindex_from s i c] returns the index of the
-    last occurrence of character [c] in string [s] before position [i+1].
-    [String.rindex s c] is equivalent to
-    [String.rindex_from s (String.length s - 1) c].
-
-    Raise [Invalid_argument] if [i+1] is not a valid position in [s].
-    Raise [Not_found] if [c] does not occur in [s] before position [i+1]. *)
-
 val rindex_from_opt: string -> int -> char -> int option
 (** [String.rindex_from_opt s i c] returns the index of the
     last occurrence of character [c] in string [s] before position [i+1]
diff --git a/src/proto_alpha/lib_protocol/src/script_ir_annot.ml b/src/proto_alpha/lib_protocol/src/script_ir_annot.ml
index 54825d0f2..9109ccd93 100644
--- a/src/proto_alpha/lib_protocol/src/script_ir_annot.ml
+++ b/src/proto_alpha/lib_protocol/src/script_ir_annot.ml
@@ -308,16 +308,18 @@ let parse_var_annot
 let split_last_dot = function
   | None -> None, None
   | Some `Field_annot s ->
-      try
-        let i = String.rindex s '.' in
-        let s1 = String.sub s 0 i in
-        let s2 = String.sub s (i + 1) (String.length s - i - 1) in
-        let f =
-          if Compare.String.equal s2 "car" || Compare.String.equal s2 "cdr"
-          then None
-          else Some (`Field_annot s2) in
-        Some (`Var_annot s1), f
-      with Not_found -> None, Some (`Field_annot s)
+      match String.rindex_opt s '.' with
+      | None -> None, Some (`Field_annot s)
+      | Some i ->
+          let s1 = String.sub s 0 i in
+          let s2 = String.sub s (i + 1) (String.length s - i - 1) in
+          let f =
+            if Compare.String.equal s2 "car"
+            || Compare.String.equal s2 "cdr" then
+              None
+            else
+              Some (`Field_annot s2) in
+          Some (`Var_annot s1), f
 
 let common_prefix v1 v2 =
   match v1, v2 with
diff --git a/src/proto_alpha/lib_protocol/src/storage.ml b/src/proto_alpha/lib_protocol/src/storage.ml
index 1731cf9f3..5a457d223 100644
--- a/src/proto_alpha/lib_protocol/src/storage.ml
+++ b/src/proto_alpha/lib_protocol/src/storage.ml
@@ -30,9 +30,7 @@ module Int_index = struct
   let to_path c l = string_of_int c :: l
   let of_path = function
     | [] | _ :: _ :: _ -> None
-    | [ c ] ->
-        try Some (int_of_string c)
-        with _ -> None
+    | [ c ] -> int_of_string_opt c
   type 'a ipath = 'a * t
   let args = Storage_description.One {
       rpc_arg = RPC_arg.int ;
@@ -330,12 +328,10 @@ module Roll = struct
       match Misc.take Cycle_repr.Index.path_length l with
       | None | Some (_, ([] | _ :: _ :: _ ))-> None
       | Some (l1, [l2]) ->
-          match Cycle_repr.Index.of_path l1 with
-          | None -> None
-          | Some c -> begin
-              try Some (c, int_of_string l2)
-              with _ -> None
-            end
+          match Cycle_repr.Index.of_path l1, int_of_string_opt l2 with
+          | None, _ | _, None -> None
+          | Some c, Some i -> Some (c, i)
+
     type 'a ipath = ('a * Cycle_repr.t) * int
     let left_args =
       Storage_description.One {