Index: src/natools-s_expressions-interpreters.adb
==================================================================
--- src/natools-s_expressions-interpreters.adb
+++ src/natools-s_expressions-interpreters.adb
@@ -71,11 +71,11 @@
       Self.Fallback_Name.Reset;
    end Reset_Fallback;
 
 
    not overriding procedure Execute
-     (Self : in out Interpreter;
+     (Self : in Interpreter;
       Expression : in out Lockable.Descriptor'Class;
       State : in out Shared_State;
       Context : in Shared_Context)
    is
       Event : Events.Event := Expression.Current_Event;
@@ -106,23 +106,23 @@
       end loop;
    end Execute;
 
 
    not overriding procedure Execute
-     (Self : in out Interpreter;
-      Fallback : in out Command'Class;
+     (Self : in Interpreter;
+      Fallback : in Command'Class;
       Expression : in out Lockable.Descriptor'Class;
       State : in out Shared_State;
       Context : in Shared_Context)
    is
       procedure Dispatch (Process : not null access procedure
-                            (Name : in Atom; Cmd : in out Command'Class));
-      procedure Process_Atom (Name : in Atom; Cmd : in out Command'Class);
-      procedure Process_Exp (Name : in Atom; Cmd : in out Command'Class);
+                            (Name : in Atom; Cmd : in Command'Class));
+      procedure Process_Atom (Name : in Atom; Cmd : in Command'Class);
+      procedure Process_Exp (Name : in Atom; Cmd : in Command'Class);
 
       procedure Dispatch (Process : not null access procedure
-                            (Name : in Atom; Cmd : in out Command'Class))
+                            (Name : in Atom; Cmd : in Command'Class))
       is
          procedure Process_Fallback (Name : in Atom);
 
          procedure Process_Fallback (Name : in Atom) is
          begin
@@ -137,23 +137,23 @@
          if Length > Self.Max_Length then
             Expression.Query_Atom (Process_Fallback'Access);
          else
             Cursor := Self.Commands.Find (Buffer (1 .. Length));
             if Command_Maps.Has_Element (Cursor) then
-               Self.Commands.Update_Element (Cursor, Process);
+               Command_Maps.Query_Element (Cursor, Process);
             else
                Process (Buffer (1 .. Length), Fallback);
             end if;
          end if;
       end Dispatch;
 
-      procedure Process_Atom (Name : in Atom; Cmd : in out Command'Class) is
+      procedure Process_Atom (Name : in Atom; Cmd : in Command'Class) is
       begin
          Cmd.Execute (State, Context, Name);
       end Process_Atom;
 
-      procedure Process_Exp (Name : in Atom; Cmd : in out Command'Class) is
+      procedure Process_Exp (Name : in Atom; Cmd : in Command'Class) is
          pragma Unreferenced (Name);
       begin
          Cmd.Execute (State, Context, Expression);
       end Process_Exp;
 
@@ -187,18 +187,18 @@
       end loop;
    end Execute;
 
 
    overriding procedure Execute
-     (Self : in out Interpreter;
+     (Self : in Interpreter;
       State : in out Shared_State;
       Context : in Shared_Context;
       Name : in Atom)
    is
-      procedure Process_Atom (Key : in Atom; Cmd : in out Command'Class);
+      procedure Process_Atom (Key : in Atom; Cmd : in Command'Class);
 
-      procedure Process_Atom (Key : in Atom; Cmd : in out Command'Class) is
+      procedure Process_Atom (Key : in Atom; Cmd : in Command'Class) is
          pragma Unreferenced (Key);
       begin
          Cmd.Execute (State, Context, Name);
       end Process_Atom;
 
@@ -205,19 +205,19 @@
       Cursor : Command_Maps.Cursor;
    begin
       if Name'Length <= Self.Max_Length then
          Cursor := Self.Commands.Find (Name);
          if Command_Maps.Has_Element (Cursor) then
-            Self.Commands.Update_Element (Cursor, Process_Atom'Access);
+            Command_Maps.Query_Element (Cursor, Process_Atom'Access);
             return;
          end if;
       end if;
 
       if not Self.Fallback_Name.Is_Empty then
          Cursor := Self.Commands.Find (Self.Fallback_Name.Query.Data.all);
          if Command_Maps.Has_Element (Cursor) then
-            Self.Commands.Update_Element (Cursor, Process_Atom'Access);
+            Command_Maps.Query_Element (Cursor, Process_Atom'Access);
             return;
          end if;
       end if;
 
       raise Command_Not_Found
@@ -224,18 +224,18 @@
         with "Unknown command """ & To_String (Name) & '"';
    end Execute;
 
 
    overriding procedure Execute
-     (Self : in out Interpreter;
+     (Self : in Interpreter;
       State : in out Shared_State;
       Context : in Shared_Context;
       Cmd : in out Lockable.Descriptor'Class)
    is
-      procedure Process_Exp (Name : in Atom; Actual : in out Command'Class);
+      procedure Process_Exp (Name : in Atom; Actual : in Command'Class);
 
-      procedure Process_Exp (Name : in Atom; Actual : in out Command'Class) is
+      procedure Process_Exp (Name : in Atom; Actual : in Command'Class) is
          pragma Unreferenced (Name);
       begin
          Actual.Execute (State, Context, Cmd);
       end Process_Exp;
 
@@ -250,23 +250,23 @@
       Cmd.Read_Atom (Buffer, Length);
 
       if Length <= Self.Max_Length then
          Cursor := Self.Commands.Find (Buffer (1 .. Length));
          if Command_Maps.Has_Element (Cursor) then
-            Self.Commands.Update_Element (Cursor, Process_Exp'Access);
+            Command_Maps.Query_Element (Cursor, Process_Exp'Access);
             return;
          end if;
       end if;
 
       if not Self.Fallback_Name.Is_Empty then
          Cursor := Self.Commands.Find (Self.Fallback_Name.Query.Data.all);
          if Command_Maps.Has_Element (Cursor) then
-            Self.Commands.Update_Element (Cursor, Process_Exp'Access);
+            Command_Maps.Query_Element (Cursor, Process_Exp'Access);
             return;
          end if;
       end if;
 
       raise Command_Not_Found
         with "Unknown command """ & To_String (Cmd.Current_Atom) & '"';
    end Execute;
 
 end Natools.S_Expressions.Interpreters;

Index: src/natools-s_expressions-interpreters.ads
==================================================================
--- src/natools-s_expressions-interpreters.ads
+++ src/natools-s_expressions-interpreters.ads
@@ -41,19 +41,19 @@
 
 
    type Command is interface;
 
    procedure Execute
-     (Self : in out Command;
+     (Self : in Command;
       State : in out Shared_State;
       Context : in Shared_Context;
       Name : in Atom)
      is null;
       --  Execute a single argumentless command
 
    procedure Execute
-     (Self : in out Command;
+     (Self : in Command;
       State : in out Shared_State;
       Context : in Shared_Context;
       Cmd : in out Lockable.Descriptor'Class)
      is null;
       --  Execute a single command with arguments
@@ -85,33 +85,33 @@
       Name : in Atom);
 
    procedure Reset_Fallback (Self : in out Interpreter);
 
    not overriding procedure Execute
-     (Self : in out Interpreter;
+     (Self : in Interpreter;
       Expression : in out Lockable.Descriptor'Class;
       State : in out Shared_State;
       Context : in Shared_Context);
       --  Execute an expression, raising Command_Not_Found on unknown commands
 
    not overriding procedure Execute
-     (Self : in out Interpreter;
-      Fallback : in out Command'Class;
+     (Self : in Interpreter;
+      Fallback : in Command'Class;
       Expression : in out Lockable.Descriptor'Class;
       State : in out Shared_State;
       Context : in Shared_Context);
       --  Execute an expression with temporary fallback for unknown commands
 
    overriding procedure Execute
-     (Self : in out Interpreter;
+     (Self : in Interpreter;
       State : in out Shared_State;
       Context : in Shared_Context;
       Name : in Atom);
       --  Execute a single argumentless command
 
    overriding procedure Execute
-     (Self : in out Interpreter;
+     (Self : in Interpreter;
       State : in out Shared_State;
       Context : in Shared_Context;
       Cmd : in out Lockable.Descriptor'Class);
       --  Execute a single command with arguments
 

Index: tests/natools-s_expressions-interpreter_tests.adb
==================================================================
--- tests/natools-s_expressions-interpreter_tests.adb
+++ tests/natools-s_expressions-interpreter_tests.adb
@@ -62,11 +62,11 @@
    ----------------------
    -- Recorder Command --
    ----------------------
 
    overriding procedure Execute
-     (Self : in out Recorder;
+     (Self : in Recorder;
       State : in out Printers.Printer'Class;
       Context : in Boolean;
       Name : in Atom)
    is
       pragma Unreferenced (Self);
@@ -76,11 +76,11 @@
       end if;
    end Execute;
 
 
    overriding procedure Execute
-     (Self : in out Recorder;
+     (Self : in Recorder;
       State : in out Printers.Printer'Class;
       Context : in Boolean;
       Cmd : in out Lockable.Descriptor'Class)
    is
       pragma Unreferenced (Self);
@@ -105,11 +105,11 @@
    --------------------
    -- Raiser Command --
    --------------------
 
    overriding procedure Execute
-     (Self : in out Raiser;
+     (Self : in Raiser;
       State : in out Printers.Printer'Class;
       Context : in Boolean;
       Name : in Atom)
    is
       pragma Unreferenced (Self, State, Context, Name);
@@ -117,11 +117,11 @@
       raise Special_Exception;
    end Execute;
 
 
    overriding procedure Execute
-     (Self : in out Raiser;
+     (Self : in Raiser;
       State : in out Printers.Printer'Class;
       Context : in Boolean;
       Cmd : in out Lockable.Descriptor'Class)
    is
       pragma Unreferenced (Self, State, Context, Cmd);
@@ -153,11 +153,11 @@
 
    procedure Test_Basic_Usage (Report : in out NT.Reporter'Class) is
       Test : NT.Test := Report.Item ("Basic usage");
    begin
       declare
-         Inter : Test_Interpreters.Interpreter := Test_Interpreter;
+         Inter : constant Test_Interpreters.Interpreter := Test_Interpreter;
          Buffer : aliased Test_Tools.Memory_Stream;
          Printer : Printers.Canonical (Buffer'Access);
          Input : Caches.Reference;
          Cursor : Caches.Cursor;
       begin
@@ -194,11 +194,11 @@
 
    procedure Test_Exception_Fallback (Report : in out NT.Reporter'Class) is
       Test : NT.Test := Report.Item ("Local fallback raising an exception");
    begin
       declare
-         Inter : Test_Interpreters.Interpreter := Test_Interpreter;
+         Inter : constant Test_Interpreters.Interpreter := Test_Interpreter;
          Buffer : aliased Test_Tools.Memory_Stream;
          Printer : Printers.Canonical (Buffer'Access);
          Input : Caches.Reference;
          Cursor : Caches.Cursor;
          Fallback : Raiser;
@@ -276,11 +276,11 @@
 
    procedure Test_Local_Fallback (Report : in out NT.Reporter'Class) is
       Test : NT.Test := Report.Item ("Local fallback");
    begin
       declare
-         Inter : Test_Interpreters.Interpreter := Test_Interpreter;
+         Inter : constant Test_Interpreters.Interpreter := Test_Interpreter;
          Buffer : aliased Test_Tools.Memory_Stream;
          Printer : Printers.Canonical (Buffer'Access);
          Input : Caches.Reference := Invalid_Commands;
          Cursor : Caches.Cursor := Input.First;
          Fallback : Recorder;

Index: tests/natools-s_expressions-interpreter_tests.ads
==================================================================
--- tests/natools-s_expressions-interpreter_tests.ads
+++ tests/natools-s_expressions-interpreter_tests.ads
@@ -45,33 +45,33 @@
      (Printers.Printer'Class, Boolean);
 
    type Recorder is new Test_Interpreters.Command with null record;
 
    overriding procedure Execute
-     (Self : in out Recorder;
+     (Self : in Recorder;
       State : in out Printers.Printer'Class;
       Context : in Boolean;
       Name : in Atom);
 
    overriding procedure Execute
-     (Self : in out Recorder;
+     (Self : in Recorder;
       State : in out Printers.Printer'Class;
       Context : in Boolean;
       Cmd : in out Lockable.Descriptor'Class);
 
    Special_Exception : exception;
 
    type Raiser is new Test_Interpreters.Command with null record;
 
    overriding procedure Execute
-     (Self : in out Raiser;
+     (Self : in Raiser;
       State : in out Printers.Printer'Class;
       Context : in Boolean;
       Name : in Atom);
 
    overriding procedure Execute
-     (Self : in out Raiser;
+     (Self : in Raiser;
       State : in out Printers.Printer'Class;
       Context : in Boolean;
       Cmd : in out Lockable.Descriptor'Class);
 
 end Natools.S_Expressions.Interpreter_Tests;