diff --git a/src/gnatcoll-arg_lists.adb b/src/gnatcoll-arg_lists.adb
index 8b2ff47e..b44847ec 100644
--- a/src/gnatcoll-arg_lists.adb
+++ b/src/gnatcoll-arg_lists.adb
@@ -537,11 +537,7 @@ package body GNATCOLL.Arg_Lists is
 
          if Protect_Quotes then
             for S in List (L)'Range loop
-               if List (L)(S) = '"'
-                 or else List (L)(S) = ' '
-                 or else List (L) (S) = '\'
-                 or else List (L) (S) = '''
-               then
+               if List (L) (S) in '"' | ' ' | '\' | ''' then
                   Length := Length + 1;
                end if;
             end loop;
@@ -555,13 +551,9 @@ package body GNATCOLL.Arg_Lists is
          for L in List'Range loop
             for J in List (L)'Range loop
                if Protect_Quotes then
-                  if List (L) (J) = '"'
-                    or else List (L) (J) = ' '
-                    or else List (L) (J) = '\'
-                    or else List (L) (J) = '''
-                  then
+                  if List (L) (J) in '"' | ' ' | '\' | ''' then
                      S (Index) := '\';
-                     Index := Index + 1;
+                     Index     := Index + 1;
                   end if;
                end if;
                S (Index) := List (L)(J);
diff --git a/src/gnatcoll-coders-base64.adb b/src/gnatcoll-coders-base64.adb
index df0dbcf3..dda6bcb3 100644
--- a/src/gnatcoll-coders-base64.adb
+++ b/src/gnatcoll-coders-base64.adb
@@ -333,7 +333,7 @@ package body GNATCOLL.Coders.Base64 is
 
    overriding function Finished (Coder : Decoder_Type) return Boolean is
    begin
-      return Coder.Finish and not Coder.Has;
+      return Coder.Finish and then not Coder.Has;
    end Finished;
 
    -----------
diff --git a/src/gnatcoll-email-mailboxes.adb b/src/gnatcoll-email-mailboxes.adb
index 631d2f4f..621c3292 100644
--- a/src/gnatcoll-email-mailboxes.adb
+++ b/src/gnatcoll-email-mailboxes.adb
@@ -703,7 +703,7 @@ package body GNATCOLL.Email.Mailboxes is
       is
          C : Container_Access;
       begin
-         if Parent_Cont = null or else Parent_Cont = Cont then
+         if Parent_Cont in null | Cont then
             return;
          end if;
 
diff --git a/src/gnatcoll-email-parser.adb b/src/gnatcoll-email-parser.adb
index 58b06426..ca61bbda 100644
--- a/src/gnatcoll-email-parser.adb
+++ b/src/gnatcoll-email-parser.adb
@@ -50,7 +50,7 @@ package body GNATCOLL.Email.Parser is
 
       case N (N'First) is
          when 'c' =>
-            return N = "cc" or else N = "content-type";
+            return N in "cc" | "content-type";
          when 'd' =>
             return N = "date";
          when 'f' =>
@@ -58,9 +58,9 @@ package body GNATCOLL.Email.Parser is
          when 'i' =>
             return N = "in-reply-to";
          when 'm' =>
-            return N = "message-id" or else N = "mime-version";
+            return N in "message-id" | "mime-version";
          when 'r' =>
-            return N = "references" or else N = "reply-to";
+            return N in "references" | "reply-to";
          when 's' =>
             return N = "subject";
          when 't' =>
diff --git a/src/gnatcoll-email-utils.adb b/src/gnatcoll-email-utils.adb
index 8833fa50..f3c4c831 100644
--- a/src/gnatcoll-email-utils.adb
+++ b/src/gnatcoll-email-utils.adb
@@ -240,7 +240,7 @@ package body GNATCOLL.Email.Utils is
    is
       Start : constant Integer := Index;
    begin
-      if S (Index) = '-' or else S (Index) = '+' then
+      if S (Index) in '-' | '+' then
          Index := Index + 1;
       end if;
 
@@ -360,11 +360,9 @@ package body GNATCOLL.Email.Utils is
       begin
          --  Timezone (we might have none in badly formed dates)
          if Index < Date'Last then
-            if Date (Index) = '-' or else Date (Index) = '+' or else
-               Date (Index) in '0' .. '9'
-            then
-               Read_Integer (Date (Index .. Date'Last), Index,
-                             Value => TZ_Local);
+            if Date (Index) in '-' | '+' | '0' .. '9' then
+               Read_Integer
+                 (Date (Index .. Date'Last), Index, Value => TZ_Local);
                TZ := Time_Offset ((TZ_Local / 100) * 60 + TZ_Local mod 100);
             else
 
@@ -380,8 +378,9 @@ package body GNATCOLL.Email.Utils is
                then
                   TZ := 0;
                else
-                  TZ := Named_TZ_Offset
-                    (Named_TZ'Value (Date (Index .. Index + 2)));
+                  TZ :=
+                    Named_TZ_Offset
+                      (Named_TZ'Value (Date (Index .. Index + 2)));
                end if;
             end if;
          end if;
@@ -642,10 +641,7 @@ package body GNATCOLL.Email.Utils is
       --  Skip spaces
 
       while From <= Str'Last
-        and then (Str (From) = ASCII.LF
-                  or else Str (From) = ASCII.CR
-                  or else Str (From) = ASCII.HT
-                  or else Str (From) = ' ')
+        and then (Str (From) in ASCII.LF | ASCII.CR | ASCII.HT | ' ')
       loop
          From := From + 1;
       end loop;
@@ -682,15 +678,11 @@ package body GNATCOLL.Email.Utils is
 
             --  ',' is the standard separator in mail messages, but ';' is
             --  often used by users when manually typing a list of addresses
-            elsif Str (From) = ','
-              or else Str (From) = ';'
-              or else Str (From) = ASCII.LF
-              or else Str (From) = ASCII.CR
-              or else Str (From) = ASCII.HT
+            elsif Str (From) in ',' | ';' | ASCII.LF | ASCII.CR | ASCII.HT
               or else (Buffer_Has_At and then Str (From) = ' ')
             then
                --  End of current address
-               From := From + 1;
+               From  := From + 1;
                Found := True;
                return;
 
@@ -1180,12 +1172,10 @@ package body GNATCOLL.Email.Utils is
        Is_EOL : Boolean) return Boolean
    is
    begin
-      if Char = ' ' or else Char = ASCII.HT then
+      if Char in ' ' | ASCII.HT then
          return Is_EOL or else Where in Any_Header;
 
-      elsif Char = '='
-              or else Char = '?'
-              or else Character'Pos (Char) not in 32 .. 126
+      elsif Char in '=' | '?' or else Character'Pos (Char) not in 32 .. 126
       then
          return True;
 
@@ -1211,7 +1201,7 @@ package body GNATCOLL.Email.Utils is
 
          --  No need to quote whitespace unless at EOL
 
-         if (Str (J) = ' ' or else Str (J) = ASCII.HT) and then not EOL then
+         if (Str (J) in ' ' | ASCII.HT) and then not EOL then
             null;
 
          elsif Needs_Quoting (Str (J), Where, EOL) then
@@ -1695,27 +1685,14 @@ package body GNATCOLL.Email.Utils is
 
       if Set = Charset_US_ASCII then
          Encoding := Encoding_7bit;
-      elsif Set = Charset_ISO_8859_1
-        or else Set = "latin_1" or else Set = "latin-1"
-        or else Set = Charset_ISO_8859_2
-        or else Set = "latin_2" or else Set = "latin-2"
-        or else Set = Charset_ISO_8859_3
-        or else Set = "latin_3" or else Set = "latin-3"
-        or else Set = Charset_ISO_8859_4
-        or else Set = "latin_4" or else Set = "latin-4"
-        or else Set = Charset_ISO_8859_9
-        or else Set = "latin_5" or else Set = "latin-5"
-        or else Set = Charset_ISO_8859_10
-        or else Set = "latin_6" or else Set = "latin-6"
-        or else Set = Charset_ISO_8859_13
-        or else Set = "latin_7" or else Set = "latin-7"
-        or else Set = Charset_ISO_8859_14
-        or else Set = "latin_8" or else Set = "latin-8"
-        or else Set = Charset_ISO_8859_15
-        or else Set = "latin_9" or else Set = "latin-9"
-        or else Set = Charset_Windows_1252
-        or else Set = "viscii"
-        or else Set = Charset_UTF_8 or else Set = "utf8"
+      elsif Set in Charset_ISO_8859_1 | "latin_1" | "latin-1" |
+            Charset_ISO_8859_2 | "latin_2" | "latin-2" | Charset_ISO_8859_3 |
+            "latin_3" | "latin-3" | Charset_ISO_8859_4 | "latin_4" |
+            "latin-4" | Charset_ISO_8859_9 | "latin_5" | "latin-5" |
+            Charset_ISO_8859_10 | "latin_6" | "latin-6" | Charset_ISO_8859_13 |
+            "latin_7" | "latin-7" | Charset_ISO_8859_14 | "latin_8" |
+            "latin-8" | Charset_ISO_8859_15 | "latin_9" | "latin-9" |
+            Charset_Windows_1252 | "viscii" | Charset_UTF_8 | "utf8"
       then
          Encoding := Encoding_QP;
       else
diff --git a/src/gnatcoll-email.adb b/src/gnatcoll-email.adb
index a3312f0d..4426dbb7 100644
--- a/src/gnatcoll-email.adb
+++ b/src/gnatcoll-email.adb
@@ -136,12 +136,7 @@ package body GNATCOLL.Email is
       L_Name : constant String := To_Lower (Name);
    begin
 
-      if L_Name = "from"
-           or else L_Name = "sender"
-           or else L_Name = "to"
-           or else L_Name = "cc"
-           or else L_Name = "bcc"
-      then
+      if L_Name in "from" | "sender" | "to" | "cc" | "bcc" then
          return Addr_Header;
       else
          return Other_Header;
@@ -154,7 +149,7 @@ package body GNATCOLL.Email is
 
    function Is_Whitespace (Char : Character) return Boolean is
    begin
-      return Char = ' ' or Char = ASCII.HT;
+      return Char in ' ' | ASCII.HT;
    end Is_Whitespace;
 
    ----------------------
@@ -1297,7 +1292,7 @@ package body GNATCOLL.Email is
          end if;
 
       else
-         if MIME_Type /= "" and not Prepend then
+         if MIME_Type /= "" and then not Prepend then
             Replace_Header (Msg, H_CT);
             if H_CTE = Null_Header then
                Delete_Headers (Msg, Content_Transfer_Encoding);
diff --git a/src/gnatcoll-geometry.adb b/src/gnatcoll-geometry.adb
index 6ca2c245..fb43081f 100644
--- a/src/gnatcoll-geometry.adb
+++ b/src/gnatcoll-geometry.adb
@@ -346,11 +346,10 @@ package body GNATCOLL.Geometry is
       Bis2 : constant Line := Bisector (Segment'(1 => P2, 2 => P3));
       Center : constant Point := Intersection (Bis1, Bis2);
    begin
-      if Center = No_Point or else Center = Infinity_Points then
+      if Center in No_Point | Infinity_Points then
          return No_Circle;
       else
-         return (Center => Center,
-                 Radius => Distance (Center, P1));
+         return (Center => Center, Radius => Distance (Center, P1));
       end if;
    end To_Circle;
 
diff --git a/src/gnatcoll-io-native.adb b/src/gnatcoll-io-native.adb
index 798253d4..8be06f68 100644
--- a/src/gnatcoll-io-native.adb
+++ b/src/gnatcoll-io-native.adb
@@ -664,16 +664,13 @@ package body GNATCOLL.IO.Native is
          GNAT.Directory_Operations.Read (D, Item, Last);
          exit when Last = 0;
 
-         if Item (1 .. Last) /= "."
-           and then Item (1 .. Last) /= ".."
+         if Item (1 .. Last) not in "." | ".."
            and then
-             (not Dirs_Only
-              or else
-                GNAT.OS_Lib.Is_Directory (Name & Item (1 .. Last)))
+           (not Dirs_Only
+            or else GNAT.OS_Lib.Is_Directory (Name & Item (1 .. Last)))
            and then
-             (not Files_Only
-              or else
-                GNAT.OS_Lib.Is_Regular_File (Name & Item (1 .. Last)))
+           (not Files_Only
+            or else GNAT.OS_Lib.Is_Regular_File (Name & Item (1 .. Last)))
          then
             if Ret = null then
                Ret := new GNAT.Strings.String_List (1 .. 10);
@@ -685,7 +682,7 @@ package body GNATCOLL.IO.Native is
                Ret := Tmp;
             end if;
 
-            N := N + 1;
+            N       := N + 1;
             Ret (N) := new String'(Item (1 .. Last));
          end if;
       end loop;
diff --git a/src/gnatcoll-io-remote-unix.adb b/src/gnatcoll-io-remote-unix.adb
index 5ec5f5cf..547db4f3 100644
--- a/src/gnatcoll-io-remote-unix.adb
+++ b/src/gnatcoll-io-remote-unix.adb
@@ -677,8 +677,7 @@ package body GNATCOLL.IO.Remote.Unix is
             exit when Matched (0) = No_Match;
             Index := Matched (1).Last + 1;
 
-            if Output (Matched (1).First .. Matched (1).Last) /= "."
-              and then Output (Matched (1).First .. Matched (1).Last) /= ".."
+            if Output (Matched (1).First .. Matched (1).Last) not in "." | ".."
             then
                Nb_Files := Nb_Files + 1;
             end if;
@@ -696,12 +695,12 @@ package body GNATCOLL.IO.Remote.Unix is
                exit when Matched (0) = No_Match;
                Index := Matched (1).Last + 1;
 
-               if Output (Matched (1).First .. Matched (1).Last) /= "."
-                 and then Output (Matched (1).First .. Matched (1).Last)
-                           /= ".."
+               if Output (Matched (1).First .. Matched (1).Last) not in "." |
+                     ".."
                then
-                  List (File_Idx) := new String'
-                    (Output (Matched (1).First .. Matched (1).Last));
+                  List (File_Idx) :=
+                    new String'
+                      (Output (Matched (1).First .. Matched (1).Last));
                   File_Idx := File_Idx + 1;
                end if;
             end loop;
diff --git a/src/gnatcoll-io-remote-windows.adb b/src/gnatcoll-io-remote-windows.adb
index fb7a57a4..479c2111 100644
--- a/src/gnatcoll-io-remote-windows.adb
+++ b/src/gnatcoll-io-remote-windows.adb
@@ -276,7 +276,7 @@ package body GNATCOLL.IO.Remote.Windows is
       Exec.Execute_Remotely (Args, Output, Status);
       Free (Args);
 
-      if Status and Output /= null then
+      if Status and then Output /= null then
          S := GNATCOLL.Utils.Split (Output.all, ' ');
 
          begin
@@ -760,8 +760,7 @@ package body GNATCOLL.IO.Remote.Windows is
             exit when Matched (0) = No_Match;
             Index := Matched (1).Last + 1;
 
-            if Output (Matched (1).First .. Matched (1).Last) /= "."
-              and then Output (Matched (1).First .. Matched (1).Last) /= ".."
+            if Output (Matched (1).First .. Matched (1).Last) not in "." | ".."
             then
                Nb_Files := Nb_Files + 1;
             end if;
@@ -779,12 +778,12 @@ package body GNATCOLL.IO.Remote.Windows is
                exit when Matched (0) = No_Match;
                Index := Matched (1).Last + 1;
 
-               if Output (Matched (1).First .. Matched (1).Last) /= "."
-                 and then Output (Matched (1).First .. Matched (1).Last)
-                           /= ".."
+               if Output (Matched (1).First .. Matched (1).Last) not in "." |
+                     ".."
                then
-                  List (File_Idx) := new String'
-                    (Output (Matched (1).First .. Matched (1).Last));
+                  List (File_Idx) :=
+                    new String'
+                      (Output (Matched (1).First .. Matched (1).Last));
                   File_Idx := File_Idx + 1;
                end if;
             end loop;
diff --git a/src/gnatcoll-io-remote.adb b/src/gnatcoll-io-remote.adb
index 32f6fba6..60fa0f77 100644
--- a/src/gnatcoll-io-remote.adb
+++ b/src/gnatcoll-io-remote.adb
@@ -54,7 +54,7 @@ package body GNATCOLL.IO.Remote is
    begin
       --  Regexps might return file strings with a trailing CR or LF. Let's
       --  remove those before creating the File record.
-      while Path (Last) = ASCII.CR or Path (Last) = ASCII.LF loop
+      while Path (Last) in ASCII.CR | ASCII.LF loop
          Last := Last - 1;
       end loop;
 
diff --git a/src/gnatcoll-memory.adb b/src/gnatcoll-memory.adb
index 2bb3bad7..46b9df59 100644
--- a/src/gnatcoll-memory.adb
+++ b/src/gnatcoll-memory.adb
@@ -110,7 +110,7 @@ package body GNATCOLL.Memory is
    procedure Free (Ptr : System.Address) is
    begin
 
-      if Ptr /= System.Null_Address and not Memory_Check then
+      if Ptr /= System.Null_Address and then not Memory_Check then
          if Memory_Monitor then
 
             Initialize_System_Memory_Debug_Pool;
@@ -287,9 +287,8 @@ package body GNATCOLL.Memory is
 
       Memory_Check := Disable_Free;
 
-      if Activate_Monitor and not Memory_Monitor then
-         Initialize_System_Memory_Debug_Pool
-           (Has_Unhandled_Memory => True);
+      if Activate_Monitor and then not Memory_Monitor then
+         Initialize_System_Memory_Debug_Pool (Has_Unhandled_Memory => True);
          Memory_Monitor := True;
       end if;
 
diff --git a/src/gnatcoll-mmap.adb b/src/gnatcoll-mmap.adb
index 278150c7..fcb0b27d 100644
--- a/src/gnatcoll-mmap.adb
+++ b/src/gnatcoll-mmap.adb
@@ -409,7 +409,7 @@ package body GNATCOLL.Mmap is
 
    function Is_Mutable (Region : Mapped_Region) return Boolean is
    begin
-      return Region.Mutable or Region.Write;
+      return Region.Mutable or else Region.Write;
    end Is_Mutable;
 
    ----------------
diff --git a/src/gnatcoll-opt_parse.adb b/src/gnatcoll-opt_parse.adb
index d7f3fea7..a605f699 100644
--- a/src/gnatcoll-opt_parse.adb
+++ b/src/gnatcoll-opt_parse.adb
@@ -149,7 +149,7 @@ package body GNATCOLL.Opt_Parse is
      (Self : Flag_Parser) return String
    is
    begin
-      if Self.Long /= "" and Self.Short /= "" then
+      if Self.Long /= "" and then Self.Short /= "" then
          return
            "[" & To_String (Self.Long) & "|" & To_String (Self.Short) & "]";
       elsif Self.Long /= "" then
@@ -166,7 +166,7 @@ package body GNATCOLL.Opt_Parse is
      (Self : Flag_Parser) return String
    is
    begin
-      if Self.Long /= "" and Self.Short /= "" then
+      if Self.Long /= "" and then Self.Short /= "" then
          return To_String (Self.Long) & ", " & To_String (Self.Short);
       elsif Self.Long /= "" then
          return To_String (Self.Long);
@@ -732,13 +732,12 @@ package body GNATCOLL.Opt_Parse is
       Result : in out Parsed_Arguments) return Parser_Return
    is
    begin
-      if Args (Pos) = Self.Long or else Args (Pos) = Self.Short then
+      if Args (Pos) in Self.Long | Self.Short then
 
          declare
-            Res : constant Parser_Result_Access := new Flag_Parser_Result'
-              (Start_Pos => Pos,
-               End_Pos   => Pos,
-               Result    =>  True);
+            Res : constant Parser_Result_Access :=
+              new Flag_Parser_Result'
+                (Start_Pos => Pos, End_Pos => Pos, Result => True);
          begin
             Result.Ref.Get.Results (Self.Position) := Res;
          end;
@@ -789,10 +788,10 @@ package body GNATCOLL.Opt_Parse is
       end Get;
 
    begin
-      if Long = "" and Short = "" then
+      if Long = "" and then Short = "" then
          raise Opt_Parse_Error
            with "A long or short flag must be provided for Parse_Flag";
-      elsif Long = "" and Name = "" then
+      elsif Long = "" and then Name = "" then
          raise Opt_Parse_Error
            with "Either Long or Name must be provided for Parse_Flag";
       elsif Enabled then
@@ -854,7 +853,7 @@ package body GNATCOLL.Opt_Parse is
            (if Name /= "" then Name else To_Upper (+Self.Name));
       begin
          if Usage_Text = "" then
-            if Long /= "" and Short /= "" then
+            if Long /= "" and then Short /= "" then
                return "[" & Long & "|" & Short & " " & Usage_Name & "]";
             elsif Long /= "" then
                return "[" & Long & " " & Usage_Name & "]";
@@ -872,7 +871,7 @@ package body GNATCOLL.Opt_Parse is
         (Dummy : Option_Parser) return String
       is
       begin
-         if Long /= "" and Short /= "" then
+         if Long /= "" and then Short /= "" then
             return Long & ", " & Short;
          elsif Long /= "" then
             return Long;
@@ -932,10 +931,10 @@ package body GNATCOLL.Opt_Parse is
       end Parse_Args;
 
    begin
-      if Long = "" and Short = "" then
+      if Long = "" and then Short = "" then
          raise Opt_Parse_Error
            with "A long or short flag must be provided for Parse_Option";
-      elsif Long = "" and Name = "" then
+      elsif Long = "" and then Name = "" then
          raise Opt_Parse_Error
            with "Either Long or Name must be provided for Parse_Option";
       elsif Enabled then
@@ -998,10 +997,10 @@ package body GNATCOLL.Opt_Parse is
       renames Internal_Option.Get;
 
    begin
-      if Long = "" and Short = "" then
+      if Long = "" and then Short = "" then
          raise Opt_Parse_Error
            with "A long or short flag must be provided for Parse_Enum_Option";
-      elsif Long = "" and Name = "" then
+      elsif Long = "" and then Name = "" then
          raise Opt_Parse_Error
            with "Either Long or Name must be provided for Parse_Enum_Option";
       end if;
@@ -1062,12 +1061,14 @@ package body GNATCOLL.Opt_Parse is
       is
       begin
          if Usage_Text = "" then
-            if Long /= "" and Short /= "" then
-               return "[" & Long & "|" & Short & " " & (+Self.Name) &
-                      " [" & (+Self.Name) & "...]]";
+            if Long /= "" and then Short /= "" then
+               return
+                 "[" & Long & "|" & Short & " " & (+Self.Name) & " [" &
+                 (+Self.Name) & "...]]";
             elsif Long /= "" then
-               return "[" & Long & " " & (+Self.Name) &
-                      " [" & (+Self.Name) & "...]]";
+               return
+                 "[" & Long & " " & (+Self.Name) & " [" & (+Self.Name) &
+                 "...]]";
             end if;
             return "[" & Short & " " & (+Self.Name) &
                    " [" & (+Self.Name) & "...]]";
@@ -1083,7 +1084,7 @@ package body GNATCOLL.Opt_Parse is
         (Dummy : Option_List_Parser) return String
       is
       begin
-         if Long /= "" and Short /= "" then
+         if Long /= "" and then Short /= "" then
             return Long & ", " & Short;
          elsif Long /= "" then
             return Long;
@@ -1163,7 +1164,7 @@ package body GNATCOLL.Opt_Parse is
             end;
          end if;
 
-         if Args (Pos) /= +Long and then Args (Pos) /= +Short then
+         if Args (Pos) not in +Long | +Short then
             return Error_Return;
          end if;
 
@@ -1192,10 +1193,10 @@ package body GNATCOLL.Opt_Parse is
       end Parse_Args;
 
    begin
-      if Long = "" and Short = "" then
+      if Long = "" and then Short = "" then
          raise Opt_Parse_Error
            with "A long or short flag must be provided for Parse_Option_List";
-      elsif Long = "" and Name = "" then
+      elsif Long = "" and then Name = "" then
          raise Opt_Parse_Error
            with "Either Long or Name must be provided for Parse_Option_List";
       elsif Enabled then
@@ -1349,7 +1350,7 @@ package body GNATCOLL.Opt_Parse is
       New_Pos     : out Parser_Return) return XString
    is
    begin
-      if Args (Pos) = Long or Args (Pos) = Short then
+      if Args (Pos) = Long or else Args (Pos) = Short then
          if Pos + 1 > Args'Last then
             raise Opt_Parse_Error with "Incomplete option";
          end if;
diff --git a/src/gnatcoll-projects-krunch.adb b/src/gnatcoll-projects-krunch.adb
index c9a4f0b3..e21a73af 100644
--- a/src/gnatcoll-projects-krunch.adb
+++ b/src/gnatcoll-projects-krunch.adb
@@ -101,18 +101,17 @@ package body GNATCOLL.Projects.Krunch is
          Buffer (2 .. Len - 5) := Buffer (7 .. Len);
          Curlen := Len - 5;
          if (Curlen >= 3 and then Buffer (Curlen - 2 .. Curlen) = "128")
-           or else (Len >= 9 and then
-                       (Buffer (3 .. 9) = "exn_lll"
-                         or else Buffer (3 .. 9) = "exp_lll"
-                         or else Buffer (3 .. 9) = "img_lll"
-                         or else Buffer (3 .. 9) = "val_lll"
-                         or else Buffer (3 .. 9) = "wid_lll"))
+           or else
+           (Len >= 9
+            and then
+            (Buffer (3 .. 9) in "exn_lll" | "exp_lll" | "img_lll" | "val_lll" |
+                 "wid_lll"))
            or else (Curlen = 10 and then Buffer (3 .. 6) = "pack")
          then
             if Len >= 15 and then Buffer (3 .. 15) = "compare_array" then
-               Buffer (3 .. 4) := "ca";
+               Buffer (3 .. 4)           := "ca";
                Buffer (5 .. Curlen - 11) := Buffer (16 .. Curlen);
-               Curlen := Curlen - 11;
+               Curlen                    := Curlen - 11;
             end if;
             Krlen := 9;
          else
@@ -163,10 +162,8 @@ package body GNATCOLL.Projects.Krunch is
          --  of predefined units use a tilde rather than a minus as the second
          --  character of the file name.
 
-      elsif Len > 1
-        and then Buffer (2) = '-'
-        and then (B1 = 'a' or else B1 = 'g' or else B1 = 'i' or else B1 = 's')
-        and then Len <= Maxlen
+      elsif Len > 1 and then Buffer (2) = '-'
+        and then (B1 in 'a' | 'g' | 'i' | 's') and then Len <= Maxlen
       then
          Buffer (2) := '~';
          return;
@@ -221,9 +218,9 @@ package body GNATCOLL.Projects.Krunch is
 
       Num_Seps := 0;
       for J in Startloc .. Curlen loop
-         if Buffer (J) = '-' or else Buffer (J) = '_' then
+         if Buffer (J) in '-' | '_' then
             Buffer (J) := ' ';
-            Num_Seps := Num_Seps + 1;
+            Num_Seps   := Num_Seps + 1;
          end if;
       end loop;
 
diff --git a/src/gnatcoll-projects.adb b/src/gnatcoll-projects.adb
index 90718331..3dbb0fad 100644
--- a/src/gnatcoll-projects.adb
+++ b/src/gnatcoll-projects.adb
@@ -1757,8 +1757,7 @@ package body GNATCOLL.Projects is
 
             Source := Element (Curs);
             loop
-               Imports := Source.Project = Project_Type (Self)
-                 or else Source.Project = No_Project;
+               Imports := Source.Project in Project_Type (Self) | No_Project;
                --  predefined source file
                if not Imports then
                   Iter := Self.Start
@@ -2487,8 +2486,8 @@ package body GNATCOLL.Projects is
             Lang := GPR.No_Name;
             NS := Tree.Env.Naming_Schemes;
             while NS /= null loop
-               if +Ext = NS.Default_Spec_Suffix.all
-                 or else +Ext = NS.Default_Body_Suffix.all
+               if +Ext in NS.Default_Spec_Suffix.all |
+                     NS.Default_Body_Suffix.all
                then
                   Lang := Get_String (NS.Language.all);
                   exit;
@@ -2692,8 +2691,7 @@ package body GNATCOLL.Projects is
       function Has_Predefined_Prefix (S : String) return Boolean is
          C : constant Character := S (S'First);
       begin
-         return S (S'First + 1) = '-'
-           and then (C = 'a' or else C = 'g' or else C = 'i' or else C = 's');
+         return S (S'First + 1) = '-' and then (C in 'a' | 'g' | 'i' | 's');
       end Has_Predefined_Prefix;
 
       Unit    : Name_Id;
@@ -3102,8 +3100,7 @@ package body GNATCOLL.Projects is
       --  Special case for the naming scheme, since we need to get access to
       --  the default registered values for foreign languages
 
-      if Attribute = Spec_Suffix_Attribute
-        or else Attribute = Specification_Suffix_Attribute
+      if Attribute in Spec_Suffix_Attribute | Specification_Suffix_Attribute
       then
          Lang := Get_Language_From_Name (View, Index);
          if Lang /= null then
@@ -3121,8 +3118,8 @@ package body GNATCOLL.Projects is
             end;
          end if;
 
-      elsif Attribute = Impl_Suffix_Attribute
-        or else Attribute = Implementation_Suffix_Attribute
+      elsif Attribute in Impl_Suffix_Attribute |
+            Implementation_Suffix_Attribute
       then
          Lang := Get_Language_From_Name (View, Index);
          if Lang /= null then
@@ -3164,19 +3161,15 @@ package body GNATCOLL.Projects is
             return "";
          end if;
 
-      elsif Attribute = Old_Implementation_Attribute
-        or else Attribute = Body_Attribute
-      then
+      elsif Attribute in Old_Implementation_Attribute | Body_Attribute then
          --  Index is a unit name
-         Unit := Units_Htable.Get
-           (Project.Tree_View.Units_HT,
-            Get_String (Index));
-         if Unit /= No_Unit_Index
-           and then Unit.File_Names (Impl) /= null
-         then
+         Unit :=
+           Units_Htable.Get (Project.Tree_View.Units_HT, Get_String (Index));
+         if Unit /= No_Unit_Index and then Unit.File_Names (Impl) /= null then
             if Unit.File_Names (Impl).Index /= 0 then
-               return Get_String (Unit.File_Names (Impl).Display_File)
-                 & " at" & Unit.File_Names (Impl).Index'Img;
+               return
+                 Get_String (Unit.File_Names (Impl).Display_File) & " at" &
+                 Unit.File_Names (Impl).Index'Img;
             else
                return Get_String (Unit.File_Names (Impl).Display_File);
             end if;
@@ -3188,18 +3181,15 @@ package body GNATCOLL.Projects is
             null;
          end if;
 
-      elsif Attribute = Old_Specification_Attribute
-        or else Attribute = Spec_Attribute
-      then
+      elsif Attribute in Old_Specification_Attribute | Spec_Attribute then
          --  Index is a unit name
-         Unit := Units_Htable.Get
-           (Project.Tree_View.Units_HT, Get_String (Index));
-         if Unit /= No_Unit_Index
-           and then Unit.File_Names (Spec) /= null
-         then
+         Unit :=
+           Units_Htable.Get (Project.Tree_View.Units_HT, Get_String (Index));
+         if Unit /= No_Unit_Index and then Unit.File_Names (Spec) /= null then
             if Unit.File_Names (Spec).Index /= 0 then
-               return Get_String (Unit.File_Names (Spec).Display_File)
-                 & " at" & Unit.File_Names (Spec).Index'Img;
+               return
+                 Get_String (Unit.File_Names (Spec).Display_File) & " at" &
+                 Unit.File_Names (Spec).Index'Img;
             else
                return Get_String (Unit.File_Names (Spec).Display_File);
             end if;
@@ -3265,7 +3255,7 @@ package body GNATCOLL.Projects is
       end if;
 
       Pkg_Id := Package_Node_Id_Of (Get_String (Lower_Pkg));
-      if Pkg_Id = Empty_Package or else Pkg_Id = Unknown_Package then
+      if Pkg_Id in Empty_Package | Unknown_Package then
          --  We don't even have such a package.
          return False;
       end if;
@@ -4950,7 +4940,7 @@ package body GNATCOLL.Projects is
             Is_Limited_With  => Is_Limited_With);
       end if;
 
-      return Imports and Is_Limited_With;
+      return Imports and then Is_Limited_With;
 
    end Is_Limited_With;
 
@@ -4978,7 +4968,7 @@ package body GNATCOLL.Projects is
             Is_Limited_With  => Is_Limited_With);
       end if;
 
-      return Imports and Is_Limited_With;
+      return Imports and then Is_Limited_With;
    end Is_Limited_With;
 
    ----------
@@ -6751,7 +6741,7 @@ package body GNATCOLL.Projects is
          Ext : constant String :=
                  GNAT.Directory_Operations.File_Extension (+Filename);
       begin
-         if  Ext = ".ads" or else Ext = ".adb" then
+         if Ext in ".ads" | ".adb" then
             return Filename'Last - 4;
          end if;
       end;
@@ -8277,8 +8267,7 @@ package body GNATCOLL.Projects is
       function Process_Gnatls (Gnatls : String) return Boolean is
       begin
          if Tree.Data.Env.Gnatls = null or else
-           (Tree.Data.Env.Gnatls.all /= Gnatls and then
-            Tree.Data.Env.Gnatls.all /= No_Gnatls)
+            (Tree.Data.Env.Gnatls.all not in Gnatls | No_Gnatls)
          then
             Tree.Data.Env.Set_Path_From_Gnatls
                (Gnatls       => Gnatls,
@@ -8452,7 +8441,7 @@ package body GNATCOLL.Projects is
          begin
             Trace (Me, "Output of gnatls is " & S);
 
-            if S = "" and Errors /= null then
+            if S = "" and then Errors /= null then
                Errors ("The output from '" & Gnatls & "-v' is empty");
             end if;
 
@@ -9768,10 +9757,8 @@ package body GNATCOLL.Projects is
                --  we must ensure that the project_id matches the view from the
                --  tree, otherwise the project will not be found by the prj*
                --  packages.
-               if P.Data.Tree.View = null
-                  or else P.Data.Tree.View = Tree
-               then
-                  P.Data.View := Proj;
+               if P.Data.Tree.View in null | Tree then
+                  P.Data.View      := Proj;
                   P.Data.Tree.View := Tree;  --  must match Proj
                end if;
             elsif Active (Me) then
@@ -9986,15 +9973,15 @@ package body GNATCOLL.Projects is
          declare
             Ls : constant String := P.Attribute_Value (Gnatlist_Attribute);
          begin
-            if Ls /= "" and then Ls /= Gnatls then
+            if Ls not in "" | Gnatls then
                --  We do not want to mark the project as incomplete for this
                --  warning, so we do not need to pass an actual Error_Handler
                GPR.Err.Error_Msg
                  (Flags => Create_Flags (null),
                   Msg   =>
-                   "?the project attribute IDE.gnatlist doesn't have"
-                  & " the same value as in the root project."
-                  & " The value """ & Gnatls & """ will be used",
+                    "?the project attribute IDE.gnatlist doesn't have" &
+                    " the same value as in the root project." &
+                    " The value """ & Gnatls & """ will be used",
                   Project => Get_View (P));
             end if;
          end;
@@ -10265,9 +10252,7 @@ package body GNATCOLL.Projects is
    function Get_Environment
      (Self : Project_Type) return Project_Environment_Access is
    begin
-      if Self = No_Project
-        or Self.Data.Tree = null
-      then
+      if Self = No_Project or else Self.Data.Tree = null then
          return null;
       else
          return Self.Data.Tree.Env;
@@ -10599,10 +10584,10 @@ package body GNATCOLL.Projects is
 
       if Lower_Pkg /= "" then
          Pkg_Id := Package_Node_Id_Of (Get_String (Lower_Pkg));
-         if Pkg_Id = Empty_Package or else Pkg_Id = Unknown_Package then
+         if Pkg_Id in Empty_Package | Unknown_Package then
             Trace (Me, "Register_New_Package (" & Lower_Pkg & ")");
-            Register_New_Package (Name  => Lower_Pkg, Id => Pkg_Id);
-            if Pkg_Id = Empty_Package or else Pkg_Id = Unknown_Package then
+            Register_New_Package (Name => Lower_Pkg, Id => Pkg_Id);
+            if Pkg_Id in Empty_Package | Unknown_Package then
                Trace (Me, "Error registering new package");
             end if;
          end if;
diff --git a/src/gnatcoll-scripts-shell.adb b/src/gnatcoll-scripts-shell.adb
index abfb0e7d..4ebebb55 100644
--- a/src/gnatcoll-scripts-shell.adb
+++ b/src/gnatcoll-scripts-shell.adb
@@ -284,7 +284,7 @@ package body GNATCOLL.Scripts.Shell is
                  (Data, "File not found: """ & Filename & '"');
          end;
 
-      elsif Command = "echo" or else Command = "echo_error" then
+      elsif Command in "echo" | "echo_error" then
          declare
             Result : Unbounded_String;
          begin
@@ -297,12 +297,10 @@ package body GNATCOLL.Scripts.Shell is
 
             if Command = "echo" then
                Insert_Text
-                 (Get_Script (Data),
-                  Txt => To_String (Result) & ASCII.LF);
+                 (Get_Script (Data), Txt => To_String (Result) & ASCII.LF);
             else
                Insert_Error
-                 (Get_Script (Data),
-                  Txt => To_String (Result) & ASCII.LF);
+                 (Get_Script (Data), Txt => To_String (Result) & ASCII.LF);
             end if;
          end;
 
@@ -577,9 +575,7 @@ package body GNATCOLL.Scripts.Shell is
 
          --  Do not display the prompt in the shell console if we did not
          --  output to it
-         if not Hide_Output
-           and then (Console = null or else Console = Old_Console)
-         then
+         if not Hide_Output and then (Console in null | Old_Console) then
             Display_Prompt (Script, Script.Console);
          end if;
       end;
@@ -1072,8 +1068,7 @@ package body GNATCOLL.Scripts.Shell is
          First := Command'First;
          while First <= Command'Last loop
             while First <= Command'Last
-              and then (Command (First) = ' '
-                        or else Command (First) = ASCII.HT)
+              and then (Command (First) in ' ' | ASCII.HT)
             loop
                First := First + 1;
             end loop;
@@ -1089,10 +1084,8 @@ package body GNATCOLL.Scripts.Shell is
             --  Search until the beginning of the next command (separated by
             --  semicolon or newline).
             while Last <= Command'Last loop
-               exit when not Quoted
-                 and then not Triple_Quoted
-                 and then (Command (Last) = ';'
-                           or else Command (Last) = ASCII.LF);
+               exit when not Quoted and then not Triple_Quoted
+                 and then (Command (Last) in ';' | ASCII.LF);
 
                if Command (Last) = '"' then
                   if Last <= Command'Last - 2
diff --git a/src/gnatcoll-scripts-utils.adb b/src/gnatcoll-scripts-utils.adb
index a60788c3..89c41736 100644
--- a/src/gnatcoll-scripts-utils.adb
+++ b/src/gnatcoll-scripts-utils.adb
@@ -48,7 +48,7 @@ package body GNATCOLL.Scripts.Utils is
             Len := Len + Args (J)'Length + 3;
 
             for T in Args (J)'Range loop
-               if Args (J)(T) = Quote or else Args (J)(T) = '\' then
+               if Args (J) (T) in Quote | '\' then
                   Len := Len + 1;
                end if;
             end loop;
@@ -215,7 +215,7 @@ package body GNATCOLL.Scripts.Utils is
             Max_Args := Max_Args * 2;
          end if;
 
-         if Start_With_Triple and End_With_Triple then
+         if Start_With_Triple and then End_With_Triple then
             New_Argv (New_Argc) :=
               new String'(Arg_String (Start_Idx + 3 .. Idx - 4));
          else
diff --git a/src/gnatcoll-scripts.adb b/src/gnatcoll-scripts.adb
index 0fe28804..a9de1d54 100644
--- a/src/gnatcoll-scripts.adb
+++ b/src/gnatcoll-scripts.adb
@@ -368,9 +368,7 @@ package body GNATCOLL.Scripts is
 
       for T in Tmp'Range loop
          if Tmp (T) = Scripting_Language (Script) then
-            if List (T) /= null
-              and then List (T) /= Data
-            then
+            if List (T) not in null | Data then
                Free (List (T));
             end if;
 
diff --git a/src/gnatcoll-strings_impl.adb b/src/gnatcoll-strings_impl.adb
index d43e1e56..02296721 100644
--- a/src/gnatcoll-strings_impl.adb
+++ b/src/gnatcoll-strings_impl.adb
@@ -1164,17 +1164,13 @@ package body GNATCOLL.Strings_Impl is
       begin
          Get_String (Self, S, L);
 
-         if Side = Ada.Strings.Both
-            or else Side = Ada.Strings.Right
-         then
+         if Side in Ada.Strings.Both | Ada.Strings.Right then
             while L >= 1 and then S (L) = Chars loop
-               L := L  - 1;
+               L := L - 1;
             end loop;
          end if;
 
-         if Side = Ada.Strings.Both
-            or else Side = Ada.Strings.Left
-         then
+         if Side in Ada.Strings.Both | Ada.Strings.Left then
             while F <= L and then S (F) = Chars loop
                F := F + 1;
             end loop;
@@ -1198,17 +1194,13 @@ package body GNATCOLL.Strings_Impl is
       begin
          Get_String (Self, S, L);
 
-         if Side = Ada.Strings.Both
-            or else Side = Ada.Strings.Right
-         then
+         if Side in Ada.Strings.Both | Ada.Strings.Right then
             while L >= 1 and then S (L) = Chars loop
-               L := L  - 1;
+               L := L - 1;
             end loop;
          end if;
 
-         if Side = Ada.Strings.Both
-            or else Side = Ada.Strings.Left
-         then
+         if Side in Ada.Strings.Both | Ada.Strings.Left then
             while F <= L and then S (F) = Chars loop
                F := F + 1;
             end loop;
diff --git a/src/gnatcoll-traces.adb b/src/gnatcoll-traces.adb
index 3aa6d7db..6d8c656e 100644
--- a/src/gnatcoll-traces.adb
+++ b/src/gnatcoll-traces.adb
@@ -423,9 +423,7 @@ package body GNATCOLL.Traces is
 
       function Stream_Name return String is
       begin
-         if Tmp.Stream /= null
-            and then Tmp.Stream /= Global.Streams_List
-         then
+         if Tmp.Stream not in null | Global.Streams_List then
             return " >" & Tmp.Stream.Name.all;
          else
             return "";
@@ -536,9 +534,9 @@ package body GNATCOLL.Traces is
                declare
                   V : constant String := To_Lower (A (A'First + 7 .. A'Last));
                begin
-                  if V = "on" or else V = "true" then
+                  if V in "on" | "true" then
                      Default_Colors := GNATCOLL.Terminal.Yes;
-                  elsif V = "off" or else V = "false" then
+                  elsif V in "off" | "false" then
                      Default_Colors := GNATCOLL.Terminal.No;
                   else
                      Default_Colors := GNATCOLL.Terminal.Auto;
@@ -983,9 +981,8 @@ package body GNATCOLL.Traces is
       if Handle.all in Trace_Decorator_Record'Class then
          Dec := Trace_Decorator (Handle);
 
-         if Dec /= Global.Colors
-            and then Dec /= Global.Finalize_Traces
-            and then Dec /= Global.Split_Lines
+         if Dec not in Global.Colors | Global.Finalize_Traces |
+               Global.Split_Lines
          then
             --  If active, store it in the list of active decorators
             if Active then
@@ -1004,7 +1001,7 @@ package body GNATCOLL.Traces is
                for A in 1 .. Global.Active_Last loop
                   if Global.Active_Decorators (A) = Dec then
                      Global.Active_Decorators (A .. Global.Active_Last - 1) :=
-                        Global.Active_Decorators (A + 1 .. Global.Active_Last);
+                       Global.Active_Decorators (A + 1 .. Global.Active_Last);
                      Global.Active_Last := Global.Active_Last - 1;
                      exit;
                   end if;
@@ -1012,9 +1009,7 @@ package body GNATCOLL.Traces is
             end if;
          end if;
 
-         if Dec = Global.Colors
-            or else Dec = Global.Absolute_Time
-            or else Dec = Global.Absolute_Date
+         if Dec in Global.Colors | Global.Absolute_Time | Global.Absolute_Date
          then
             Tmp := Global.Handles_List;
             while Tmp /= null loop
@@ -1695,10 +1690,8 @@ package body GNATCOLL.Traces is
       Status : int;
       pragma Unreferenced (Status);
    begin
-      if Stream.File /= stdout
-         and then Stream.File /= stderr
-      then
-         Status := fclose (Stream.File);
+      if Stream.File not in stdout | stderr then
+         Status      := fclose (Stream.File);
          Stream.File := NULL_Stream;
       end if;
 
diff --git a/src/gnatcoll-utils.adb b/src/gnatcoll-utils.adb
index 2a2e4a8d..cac34e08 100644
--- a/src/gnatcoll-utils.adb
+++ b/src/gnatcoll-utils.adb
@@ -60,11 +60,7 @@ package body GNATCOLL.Utils is
 
    function Is_Whitespace (Char : Character) return Boolean is
    begin
-      if Char = ' '
-        or else Char = ASCII.HT
-        or else Char = ASCII.LF
-        or else Char = ASCII.CR
-      then
+      if Char in ' ' | ASCII.HT | ASCII.LF | ASCII.CR then
          return True;
       end if;
       return False;
@@ -394,7 +390,7 @@ package body GNATCOLL.Utils is
       --  In addition to the default directory_separator allow the '/' to
       --  act as separator since this a valid path separator on Windows
       --  systems.
-      return C = GNAT.OS_Lib.Directory_Separator or else C = '/';
+      return C in GNAT.OS_Lib.Directory_Separator | '/';
    end Is_Directory_Separator;
 
    -------------------------
@@ -841,7 +837,7 @@ package body GNATCOLL.Utils is
       end if;
 
       for J in reverse Str'First .. Index loop
-         if Str (J) = ASCII.LF or else Str (J) = ASCII.CR then
+         if Str (J) in ASCII.LF | ASCII.CR then
             if J < Str'Last then
                return J + 1;
             else
@@ -861,7 +857,7 @@ package body GNATCOLL.Utils is
       Index : constant Natural := Natural'Max (Str'First, P);
    begin
       for J in Index .. Str'Last loop
-         if Str (J) = ASCII.LF or else Str (J) = ASCII.CR then
+         if Str (J) in ASCII.LF | ASCII.CR then
             return J - 1;
          end if;
       end loop;
@@ -1208,9 +1204,7 @@ package body GNATCOLL.Utils is
            and then Str (It) /= ASCII.CR
            and then Str (It) /= ASCII.LF
          loop
-            if Str (It) /= ' '
-              and then Str (It) /= ASCII.HT
-            then
+            if Str (It) not in ' ' | ASCII.HT then
                return False;
             end if;
 
diff --git a/src/gnatcoll-vfs.adb b/src/gnatcoll-vfs.adb
index 7133e209..e144cf37 100644
--- a/src/gnatcoll-vfs.adb
+++ b/src/gnatcoll-vfs.adb
@@ -1788,21 +1788,21 @@ package body GNATCOLL.VFS is
             declare
                B : constant Filesystem_String := Files (F).Base_Name;
             begin
-               if B /= "." and then B /= ".." then
+               if B not in "." | ".." then
                   if Extension = ""
-                     or else Files (F).File_Extension = Extension
+                    or else Files (F).File_Extension = Extension
                   then
                      case Filter is
-                     when Dirs_Only =>
-                        if Files (F).Is_Directory then
+                        when Dirs_Only =>
+                           if Files (F).Is_Directory then
+                              Append (Result, Files (F));
+                           end if;
+                        when Files_Only =>
+                           if Files (F).Is_Regular_File then
+                              Append (Result, Files (F));
+                           end if;
+                        when All_Files =>
                            Append (Result, Files (F));
-                        end if;
-                     when Files_Only =>
-                        if Files (F).Is_Regular_File then
-                           Append (Result, Files (F));
-                        end if;
-                     when All_Files =>
-                        Append (Result, Files (F));
                      end case;
                   end if;