...

14 files changed, 686 insertions, 87 deletions

diff --git a/src/core/src/tonkadur/Main.java b/src/core/src/tonkadur/Main.java
index 76790e9..c8f8f1b 100644
--- a/src/core/src/tonkadur/Main.java
+++ b/src/core/src/tonkadur/Main.java
@@ -2,6 +2,8 @@ package tonkadur;
 
 import java.io.IOException;
 
+import tonkadur.fate.v1.lang.World;
+
 import tonkadur.fate.v1.Utils;
 
 public class Main
@@ -12,6 +14,10 @@ public class Main
    public static void main (final String[] args)
    throws IOException
    {
-      Utils.parse_file(args[0]);
+      final World world;
+
+      world = new World();
+
+      Utils.add_file_content(args[0], world);
    }
 }
diff --git a/src/core/src/tonkadur/fate/v1/Utils.java b/src/core/src/tonkadur/fate/v1/Utils.java
index 048b3f2..562adee 100644
--- a/src/core/src/tonkadur/fate/v1/Utils.java
+++ b/src/core/src/tonkadur/fate/v1/Utils.java
@@ -29,6 +29,7 @@ public class Utils
       lexer = new FateLexer(CharStreams.fromFileName(filename));
       tokens = new CommonTokenStream(lexer);
       parser = new FateParser(tokens);
+
       parser.fate_file(world);
    }
 }
diff --git a/src/core/src/tonkadur/fate/v1/error/ConflictingDeclarationException.java b/src/core/src/tonkadur/fate/v1/error/ConflictingDeclarationException.java
new file mode 100644
index 0000000..d0837a7
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/ConflictingDeclarationException.java
@@ -0,0 +1,64 @@
+package tonkadur.fate.v1.error;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+import tonkadur.fate.v1.lang.meta.DeclaredEntity;
+
+public class ConflictingDeclarationException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final DeclaredEntity new_declaration;
+   protected final DeclaredEntity original_declaration;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public ConflictingDeclarationException
+   (
+      final DeclaredEntity new_declaration,
+      final DeclaredEntity original_declaration
+   )
+   {
+      super
+      (
+         ErrorLevel.ERROR,
+         ErrorCategory.CONFLICTING_DECLARATION,
+         new_declaration.get_origin()
+      );
+
+      this.new_declaration = new_declaration;
+      this.original_declaration = original_declaration;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.get_context().toString());
+      sb.append("Declaration for ");
+      sb.append(original_declaration.get_type_name());
+      sb.append(" '");
+      sb.append(original_declaration.get_name());
+      sb.append("' at ");
+      sb.append(origin.get_location().toString());
+      sb.append(" conflicts with its declaration at ");
+      sb.append(original_declaration.get_origin().get_location().toString());
+      sb.append(".");
+      sb.append(System.lineSeparator());
+      sb.append("Previous declaration was ");
+      sb.append(original_declaration.toString());
+      sb.append(".");
+      sb.append(System.lineSeparator());
+      sb.append("New declaration is ");
+      sb.append(new_declaration.toString());
+      sb.append(".");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/error/TypeAlreadyDeclaredException.java b/src/core/src/tonkadur/fate/v1/error/DuplicateDeclarationException.java
index 4050d1e..066bbe6 100644
--- a/src/core/src/tonkadur/fate/v1/error/TypeAlreadyDeclaredException.java
+++ b/src/core/src/tonkadur/fate/v1/error/DuplicateDeclarationException.java
@@ -5,26 +5,26 @@ import tonkadur.error.ErrorLevel;
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
-import tonkadur.fate.v1.lang.Type;
+import tonkadur.fate.v1.lang.meta.DeclaredEntity;
 
-public class TypeAlreadyDeclaredException extends ParsingError
+public class DuplicateDeclarationException extends ParsingError
 {
    /***************************************************************************/
    /**** MEMBERS **************************************************************/
    /***************************************************************************/
-   protected final Type original_type;
+   protected final DeclaredEntity original_declaration;
 
    /***************************************************************************/
    /**** PUBLIC ***************************************************************/
    /***************************************************************************/
-   public TypeAlreadyDeclaredException
+   public DuplicateDeclarationException
    (
       final Origin origin,
-      final Type original_type
+      final DeclaredEntity original_declaration
    )
    {
       super(ErrorLevel.WARNING, ErrorCategory.DUPLICATE_DECLARATION, origin);
-      this.original_type = original_type;
+      this.original_declaration = original_declaration;
    }
 
    @Override
@@ -33,12 +33,14 @@ public class TypeAlreadyDeclaredException extends ParsingError
       final StringBuilder sb = new StringBuilder();
 
       sb.append(origin.get_context().toString());
-      sb.append("Declaration for type '");
-      sb.append(original_type.get_name());
+      sb.append("Declaration for ");
+      sb.append(original_declaration.get_type_name());
+      sb.append(" '");
+      sb.append(original_declaration.get_name());
       sb.append("' at ");
       sb.append(origin.get_location().toString());
       sb.append(" when it was already declared at ");
-      sb.append(original_type.get_origin().get_location().toString());
+      sb.append(original_declaration.get_origin().get_location().toString());
       sb.append(".");
 
       return sb.toString();
diff --git a/src/core/src/tonkadur/fate/v1/error/ErrorCategory.java b/src/core/src/tonkadur/fate/v1/error/ErrorCategory.java
index f56b6d5..ef1396e 100644
--- a/src/core/src/tonkadur/fate/v1/error/ErrorCategory.java
+++ b/src/core/src/tonkadur/fate/v1/error/ErrorCategory.java
@@ -4,7 +4,7 @@ class ErrorCategory extends tonkadur.error.ErrorCategory
 {
    public static final ErrorCategory DUPLICATE_DECLARATION;
    public static final ErrorCategory CONFLICTING_DECLARATION;
-   public static final ErrorCategory UNDECLARED;
+   public static final ErrorCategory MISSING_DECLARATION;
    public static final ErrorCategory UNKNOWN_SEQUENCE;
    public static final ErrorCategory INCORRECT_TYPE;
    public static final ErrorCategory INCOMPATIBLE_TYPE;
@@ -13,7 +13,7 @@ class ErrorCategory extends tonkadur.error.ErrorCategory
    {
       DUPLICATE_DECLARATION = new ErrorCategory("duplicate_declaration");
       CONFLICTING_DECLARATION = new ErrorCategory("conflicting_declaration");
-      UNDECLARED = new ErrorCategory("undeclared");
+      MISSING_DECLARATION = new ErrorCategory("missing_declaration");
       UNKNOWN_SEQUENCE = new ErrorCategory("unknown_sequence");
       INCORRECT_TYPE = new ErrorCategory("incorrect_type");
       INCOMPATIBLE_TYPE = new ErrorCategory("incompatible_type");
diff --git a/src/core/src/tonkadur/fate/v1/error/IncompatibleDeclarationException.java b/src/core/src/tonkadur/fate/v1/error/IncompatibleDeclarationException.java
new file mode 100644
index 0000000..582f593
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/IncompatibleDeclarationException.java
@@ -0,0 +1,64 @@
+package tonkadur.fate.v1.error;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+import tonkadur.fate.v1.lang.meta.DeclaredEntity;
+
+public class IncompatibleDeclarationException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final DeclaredEntity new_declaration;
+   protected final DeclaredEntity original_declaration;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public IncompatibleDeclarationException
+   (
+      final DeclaredEntity new_declaration,
+      final DeclaredEntity original_declaration
+   )
+   {
+      super
+      (
+         ErrorLevel.ERROR,
+         ErrorCategory.CONFLICTING_DECLARATION,
+         new_declaration.get_origin()
+      );
+
+      this.new_declaration = new_declaration;
+      this.original_declaration = original_declaration;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.get_context().toString());
+      sb.append("Declaration for ");
+      sb.append(original_declaration.get_type_name());
+      sb.append(" '");
+      sb.append(original_declaration.get_name());
+      sb.append("' at ");
+      sb.append(origin.get_location().toString());
+      sb.append(" is incompatible with its declaration at ");
+      sb.append(original_declaration.get_origin().get_location().toString());
+      sb.append(".");
+      sb.append(System.lineSeparator());
+      sb.append("Previous declaration was ");
+      sb.append(original_declaration.toString());
+      sb.append(".");
+      sb.append(System.lineSeparator());
+      sb.append("New declaration is ");
+      sb.append(new_declaration.toString());
+      sb.append(".");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/error/MissingDeclarationException.java b/src/core/src/tonkadur/fate/v1/error/MissingDeclarationException.java
new file mode 100644
index 0000000..f564fbe
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/MissingDeclarationException.java
@@ -0,0 +1,47 @@
+package tonkadur.fate.v1.error;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+public class MissingDeclarationException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final String type_name;
+   protected final String name;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public MissingDeclarationException
+   (
+      final Origin origin,
+      final String type_name,
+      final String name
+   )
+   {
+      super(ErrorLevel.ERROR, ErrorCategory.MISSING_DECLARATION, origin);
+      this.type_name = type_name;
+      this.name = name;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.get_context().toString());
+      sb.append("Unknown ");
+      sb.append(type_name);
+      sb.append(" '");
+      sb.append(name);
+      sb.append("' at ");
+      sb.append(origin.get_location().toString());
+      sb.append(".");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/lang/Event.java b/src/core/src/tonkadur/fate/v1/lang/Event.java
new file mode 100644
index 0000000..38b3210
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/lang/Event.java
@@ -0,0 +1,147 @@
+package tonkadur.fate.v1.lang;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import tonkadur.functional.Merge;
+
+import tonkadur.parser.Context;
+import tonkadur.parser.Location;
+import tonkadur.parser.Origin;
+
+import tonkadur.fate.v1.lang.meta.DeclaredEntity;
+
+public class Event extends DeclaredEntity
+{
+   protected static final Event ANY;
+
+   static
+   {
+      ANY =
+         new Event
+         (
+            new Origin(new Context(""), Location.BASE_LANGUAGE),
+            new ArrayList<Type>(),
+            /*
+             * Use of a space necessary to avoid conflicting with a user created
+             * type.
+             */
+            "undetermined event"
+         );
+   }
+
+   public static Event value_on_missing ()
+   {
+      return ANY;
+   }
+
+   @Override
+   public /* static */ String get_type_name ()
+   {
+      return "Event";
+   }
+
+
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final List<Type> signature;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+
+   /**** Constructors *********************************************************/
+   public Event
+   (
+      final Origin origin,
+      final List<Type> signature,
+      final String name
+   )
+   {
+      super(origin, name);
+
+      this.signature = signature;
+   }
+
+   /**** Accessors ************************************************************/
+   public List<Type> get_signature ()
+   {
+      return signature;
+   }
+
+   /**** Misc. ****************************************************************/
+   @Override
+   public boolean is_incompatible_with_declaration (final DeclaredEntity de)
+   {
+      if (de instanceof Event)
+      {
+         final Event e;
+
+         e = (Event) de;
+
+         if (signature.size() == e.signature.size())
+         {
+            final List<Boolean> compatibility_result;
+
+            /*
+             * Basically, the events are compatible if, and only if, the old
+             * signature is as least as restrictive as the new one.
+             */
+            compatibility_result =
+               (
+                  new Merge<Type,Type,Boolean>()
+                  {
+                     @Override
+                     protected Boolean merge_fun (final Type a, final Type b)
+                     {
+                        return
+                           new Boolean(a.is_incompatible_with_declaration(b));
+                     }
+                  }.merge(signature, e.signature)
+               );
+
+            return compatibility_result.contains(Boolean.TRUE);
+         }
+      }
+
+      return true;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(name);
+
+      if (!signature.isEmpty())
+      {
+         boolean first_argument;
+
+         sb.append(": ");
+
+         first_argument = true;
+
+         for (final Type type: signature)
+         {
+            if (first_argument)
+            {
+               first_argument = false;
+            }
+            else
+            {
+               sb.append(" -> ");
+            }
+
+            sb.append(type.get_name());
+         }
+      }
+
+      return sb.toString();
+   }
+
+   /***************************************************************************/
+   /**** PROTECTED ************************************************************/
+   /***************************************************************************/
+}
diff --git a/src/core/src/tonkadur/fate/v1/lang/Type.java b/src/core/src/tonkadur/fate/v1/lang/Type.java
index 2990dc0..269e011 100644
--- a/src/core/src/tonkadur/fate/v1/lang/Type.java
+++ b/src/core/src/tonkadur/fate/v1/lang/Type.java
@@ -1,14 +1,44 @@
 package tonkadur.fate.v1.lang;
 
+import tonkadur.parser.Context;
+import tonkadur.parser.Location;
 import tonkadur.parser.Origin;
 
-public class Type
+import tonkadur.fate.v1.lang.meta.DeclaredEntity;
+
+public class Type extends DeclaredEntity
 {
+   protected static final Type ANY;
+
+   static
+   {
+      ANY =
+         new Type
+         (
+            new Origin(new Context(""), Location.BASE_LANGUAGE),
+            null,
+            /*
+             * Use of a space necessary to avoid conflicting with a user created
+             * type.
+             */
+            "undetermined type"
+         );
+   }
+
+   public static Type value_on_missing ()
+   {
+      return ANY;
+   }
+
+   @Override
+   public /* static */ String get_type_name ()
+   {
+      return "Type";
+   }
+
    /***************************************************************************/
    /**** MEMBERS **************************************************************/
    /***************************************************************************/
-   protected final Origin origin;
-   protected final String name;
    protected final Type true_type;
    protected final Type parent;
 
@@ -24,6 +54,8 @@ public class Type
       final String name
    )
    {
+      super(origin, name);
+
       if (parent == null)
       {
          true_type = this;
@@ -33,21 +65,10 @@ public class Type
          true_type = parent.true_type;
       }
 
-      this.origin = origin;
       this.parent = parent;
-      this.name = name;
    }
 
    /**** Accessors ************************************************************/
-   public String get_name ()
-   {
-      return name;
-   }
-
-   public Origin get_origin ()
-   {
-      return origin;
-   }
 
    public Type get_true_type ()
    {
@@ -72,24 +93,22 @@ public class Type
 
    /**** Misc. ****************************************************************/
    @Override
-   public boolean equals (final Object o)
+   public boolean is_incompatible_with_declaration (final DeclaredEntity de)
    {
-      if (o instanceof Type)
+      if (de instanceof Type)
       {
          final Type t;
 
-         t = (Type) o;
+         t = (Type) de;
 
-         return name.equals(t.name);
+         /*
+          * If the previous type cannot be used when the new one will do, the
+          * new declaration cannot safely stand.
+          */
+         return !can_be_used_as(t);
       }
 
-      return false;
-   }
-
-   @Override
-   public int hashCode ()
-   {
-      return name.hashCode();
+      return true;
    }
 
    @Override
diff --git a/src/core/src/tonkadur/fate/v1/lang/World.java b/src/core/src/tonkadur/fate/v1/lang/World.java
index cd42f55..e6bf2d6 100644
--- a/src/core/src/tonkadur/fate/v1/lang/World.java
+++ b/src/core/src/tonkadur/fate/v1/lang/World.java
@@ -1,9 +1,14 @@
 package tonkadur.fate.v1.lang;
 
-import tonkadur.fate.v1.error.EventAlreadyDeclaredException;
-import tonkadur.fate.v1.error.TypeAlreadyDeclaredException;
-import tonkadur.fate.v1.error.TextEffectAlreadyDeclaredException;
-import tonkadur.fate.v1.error.UnknownTypeException;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.List;
+
+import tonkadur.parser.Context;
+import tonkadur.parser.Location;
+import tonkadur.parser.Origin;
+
+import tonkadur.fate.v1.lang.meta.DeclarationCollection;
 
 public class World
 {
@@ -11,12 +16,12 @@ public class World
    /**** MEMBERS **************************************************************/
    /***************************************************************************/
    protected final Collection<String> loaded_files;
-   protected final Map<String, Event> events;
-   protected final Map<String, Macro> macros;
-   protected final Map<String, Sequence> sequences;
-   protected final Map<String, TextEffect> text_effects;
-   protected final Map<String, Type> types;
-   protected final Map<String, Variable> variables;
+   protected final DeclarationCollection<Event> event_collection;
+//   protected final DeclarationCollection<Macro> macros;
+//   protected final DeclarationCollection<Sequence> sequences;
+//   protected final DeclarationCollection<TextEffect> text_effects;
+   protected final DeclarationCollection<Type> type_collection;
+//   protected final DeclarationCollection<Variable> variables;
 
    /***************************************************************************/
    /**** PUBLIC ***************************************************************/
@@ -27,12 +32,14 @@ public class World
    {
       loaded_files = new HashSet<String>();
 
-      events = new HashMap<String, Event>();
-      macros = new HashMap<String, Macro>();
-      sequences = new HashMap<String, Sequence>();
-      text_effects = new HashMap<String, TextEffect>();
-      types = new HashMap<String, Type>();
-      variables = new HashMap<String, Variable>();
+      event_collection =
+         new DeclarationCollection<Event>(Event.value_on_missing());
+      //macros = new DeclarationCollection<Macro>();
+      //sequences = new DeclarationCollection<Sequence>();
+      //text_effects = new DeclarationCollection<TextEffect>();
+      type_collection =
+         new DeclarationCollection<Type>(Type.value_on_missing());
+      //variables = new DeclarationCollection<Variable>();
 
       add_base_types();
    }
@@ -41,7 +48,7 @@ public class World
    /**** Loaded Files ****/
    public Collection<String> get_loaded_files ()
    {
-      return loaded_files.clone();
+      return loaded_files;
    }
 
    public boolean has_loaded_file (final String name)
@@ -54,36 +61,14 @@ public class World
       loaded_files.add(name);
    }
 
-   /**** Events ****/
-   public Collection<Event> get_events ()
+   public DeclarationCollection<Type> types()
    {
-      return events.values();
+      return type_collection;
    }
 
-   public boolean has_event (final String name)
+   public DeclarationCollection<Event> events()
    {
-      return events.containsKey(name);
-   }
-
-   public void add_event
-   (
-      final Origin origin,
-      final String name,
-      final List<Type> parameter_types
-   )
-   throws EventAlreadyDeclaredException, UnknownTypeException
-   {
-      if (has_event(name))
-      {
-         
-      }
-      for (final Type t: parameter_types)
-      {
-         if (!has_type(t))
-         {
-            throw new UnknownTypeException()
-         }
-      }
+      return event_collection;
    }
 
    /**** Misc. ****************************************************************/
@@ -97,11 +82,20 @@ public class World
 
       base = new Origin(new Context(""), Location.BASE_LANGUAGE);
 
-      add_type(base, null, "dict");
-      add_type(base, null, "float");
-      add_type(base, null, "int");
-      add_type(base, null, "list");
-      add_type(base, null, "set");
-      add_type(base, null, "string");
+      try
+      {
+         type_collection.add(new Type(base, null, "dict"));
+         type_collection.add(new Type(base, null, "float"));
+         type_collection.add(new Type(base, null, "int"));
+         type_collection.add(new Type(base, null, "list"));
+         type_collection.add(new Type(base, null, "set"));
+         type_collection.add(new Type(base, null, "string"));
+      }
+      catch (final Throwable t)
+      {
+         System.err.println("Unable to add base types:" + t.toString());
+         System.exit(-1);
+      }
+
    }
 }
diff --git a/src/core/src/tonkadur/fate/v1/lang/meta/DeclarationCollection.java b/src/core/src/tonkadur/fate/v1/lang/meta/DeclarationCollection.java
new file mode 100644
index 0000000..838d109
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/lang/meta/DeclarationCollection.java
@@ -0,0 +1,119 @@
+package tonkadur.fate.v1.lang.meta;
+
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
+
+import tonkadur.error.ErrorManager;
+
+import tonkadur.parser.Origin;
+
+import tonkadur.fate.v1.error.MissingDeclarationException;
+import tonkadur.fate.v1.error.DuplicateDeclarationException;
+import tonkadur.fate.v1.error.ConflictingDeclarationException;
+import tonkadur.fate.v1.error.IncompatibleDeclarationException;
+
+public class DeclarationCollection <Declared extends DeclaredEntity>
+{
+   protected final Map<String, Declared> collection;
+   protected final Declared value_on_missing;
+
+   public DeclarationCollection (final Declared value_on_missing)
+   {
+      collection = new HashMap<String, Declared>();
+      this.value_on_missing = value_on_missing;
+   }
+
+   public Collection<Declared> get_all ()
+   {
+      return collection.values();
+   }
+
+   public boolean has (final String name)
+   {
+      return collection.containsKey(name);
+   }
+
+   public void add (final Declared entity)
+   throws
+      DuplicateDeclarationException,
+      ConflictingDeclarationException,
+      IncompatibleDeclarationException
+   {
+      assert_entity_can_be_added(entity);
+      collection.put(entity.get_name(), entity);
+   }
+
+   public Declared get (final Origin call_origin, final String name)
+   throws MissingDeclarationException
+   {
+      final Declared result;
+
+      result = collection.get(name);
+
+      if (result == null)
+      {
+         ErrorManager.handle
+         (
+            new MissingDeclarationException
+            (
+               call_origin,
+               value_on_missing.get_type_name(),
+               name
+            )
+         );
+
+         return value_on_missing;
+      }
+
+      return result;
+   }
+
+   /***************************************************************************/
+   /**** PROTECTED ************************************************************/
+   /***************************************************************************/
+   protected void assert_entity_can_be_added (final Declared new_version)
+   throws
+      DuplicateDeclarationException,
+      ConflictingDeclarationException,
+      IncompatibleDeclarationException
+   {
+      final Declared previous_version;
+
+      previous_version = collection.get(new_version.get_name());
+
+      if (previous_version == null)
+      {
+         return;
+      }
+
+      ErrorManager.handle
+      (
+         new DuplicateDeclarationException
+         (
+            new_version.get_origin(),
+            previous_version
+         )
+      );
+
+      if (!previous_version.conflicts_with_declaration(new_version))
+      {
+         return;
+      }
+
+      ErrorManager.handle
+      (
+         new ConflictingDeclarationException(new_version, previous_version)
+      );
+
+      if (!previous_version.is_incompatible_with_declaration(new_version))
+      {
+         return;
+      }
+
+      ErrorManager.handle
+      (
+         new IncompatibleDeclarationException(new_version, previous_version)
+      );
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/lang/meta/DeclaredEntity.java b/src/core/src/tonkadur/fate/v1/lang/meta/DeclaredEntity.java
new file mode 100644
index 0000000..5748391
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/lang/meta/DeclaredEntity.java
@@ -0,0 +1,88 @@
+package tonkadur.fate.v1.lang.meta;
+
+import tonkadur.parser.Origin;
+
+public abstract class DeclaredEntity
+{
+   /***************************************************************************/
+   /**** STATIC ***************************************************************/
+   /***************************************************************************/
+   /* I wish it could be static, but it can't, because of Java limitations. */
+   public /* static */ String get_type_name ()
+   {
+      return "Declared Entity";
+   }
+
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Origin origin;
+   protected final String name;
+
+   /***************************************************************************/
+   /**** PROTECTED ************************************************************/
+   /***************************************************************************/
+
+   /**** Constructors *********************************************************/
+   protected DeclaredEntity
+   (
+      final Origin origin,
+      final String name
+   )
+   {
+      this.origin = origin;
+      this.name = name;
+   }
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+
+   /**** Accessors ************************************************************/
+   public String get_name ()
+   {
+      return name;
+   }
+
+   public Origin get_origin ()
+   {
+      return origin;
+   }
+
+   public boolean conflicts_with_declaration (final DeclaredEntity de)
+   {
+      return !equals(de);
+   }
+
+   public boolean is_incompatible_with_declaration (final DeclaredEntity de)
+   {
+      return !equals(de);
+   }
+
+   @Override
+   public boolean equals (final Object o)
+   {
+      if (o instanceof DeclaredEntity)
+      {
+         final DeclaredEntity de;
+
+         de = (DeclaredEntity) o;
+
+         return toString().equals(de.toString());
+      }
+
+      return false;
+   }
+
+   @Override
+   public int hashCode ()
+   {
+      return toString().hashCode();
+   }
+
+   @Override
+   public String toString ()
+   {
+      return name;
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/parser/FateParser.g4 b/src/core/src/tonkadur/fate/v1/parser/FateParser.g4
index 408d71d..273722f 100644
--- a/src/core/src/tonkadur/fate/v1/parser/FateParser.g4
+++ b/src/core/src/tonkadur/fate/v1/parser/FateParser.g4
@@ -8,6 +8,8 @@ options
 @header
 {
    package tonkadur.fate.v1.parser;
+
+   import tonkadur.fate.v1.lang.World;
 }
 
 @members
@@ -18,7 +20,7 @@ options
 /******************************************************************************/
 /******************************************************************************/
 /******************************************************************************/
-fate_file:
+fate_file [World world]:
    WS* FATE_VERSION_KW WORD L_PAREN WS*
    (
       (first_level_fate_instr|general_fate_instr)
diff --git a/src/core/src/tonkadur/functional/Merge.java b/src/core/src/tonkadur/functional/Merge.java
new file mode 100644
index 0000000..68bb0e7
--- /dev/null
+++ b/src/core/src/tonkadur/functional/Merge.java
@@ -0,0 +1,46 @@
+package tonkadur.functional;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+/**
+ * I am not a fan of how Java implemented functional programming, so here is
+ * some alternative.
+ **/
+
+public class Merge <Input0, Input1, Output>
+{
+   public List<Output> merge (final List<Input0> i0, final List<Input1> i1)
+   {
+      final int result_size;
+      final List<Output> output;
+      final Iterator<Input0> it0;
+      final Iterator<Input1> it1;
+
+      result_size = Math.max(i0.size(), i1.size());
+      output = new ArrayList<Output>(result_size);
+
+      it0 = i0.iterator();
+      it1 = i1.iterator();
+
+      for (int i = 0; i < result_size; ++i)
+      {
+         output.add
+         (
+            merge_fun
+            (
+               it0.hasNext() ? it0.next() : null,
+               it1.hasNext() ? it1.next() : null
+            )
+         );
+      }
+
+      return output;
+   }
+
+   protected Output merge_fun (final Input0 i0, final Input1 i1)
+   {
+      return null;
+   }
+}