...

22 files changed, 935 insertions, 48 deletions

diff --git a/src/core/src/tonkadur/fate/v1/error/ConflictingDeclarationException.java b/src/core/src/tonkadur/fate/v1/error/ConflictingDeclarationException.java
index d0837a7..34e1a98 100644
--- a/src/core/src/tonkadur/fate/v1/error/ConflictingDeclarationException.java
+++ b/src/core/src/tonkadur/fate/v1/error/ConflictingDeclarationException.java
@@ -27,7 +27,7 @@ public class ConflictingDeclarationException extends ParsingError
       super
       (
          ErrorLevel.ERROR,
-         ErrorCategory.CONFLICTING_DECLARATION,
+         ErrorCategory.CONFLICTING,
          new_declaration.get_origin()
       );
 
@@ -41,7 +41,8 @@ public class ConflictingDeclarationException extends ParsingError
       final StringBuilder sb = new StringBuilder();
 
       sb.append(origin.get_context().toString());
-      sb.append("Declaration for ");
+      sb.append(error_category.toString());
+      sb.append(" Declaration for ");
       sb.append(original_declaration.get_type_name());
       sb.append(" '");
       sb.append(original_declaration.get_name());
diff --git a/src/core/src/tonkadur/fate/v1/error/ConflictingTypeException.java b/src/core/src/tonkadur/fate/v1/error/ConflictingTypeException.java
new file mode 100644
index 0000000..3cf287e
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/ConflictingTypeException.java
@@ -0,0 +1,55 @@
+package tonkadur.fate.v1.error;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+import tonkadur.fate.v1.lang.Type;
+
+public class ConflictingTypeException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Type given_type;
+   protected final Type expected_type;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public ConflictingTypeException
+   (
+      final Origin call_origin,
+      final Type given_type,
+      final Type expected_type
+   )
+   {
+      super
+      (
+         ErrorLevel.ERROR,
+         ErrorCategory.CONFLICTING,
+         call_origin
+      );
+
+      this.given_type = given_type;
+      this.expected_type = expected_type;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.get_context().toString());
+      sb.append(error_category.toString());
+      sb.append(" Resulting type '");
+      sb.append(given_type.get_name());
+      sb.append("' ");
+      sb.append(" conflicts with the expected one ('");
+      sb.append(expected_type.get_name());
+      sb.append("').");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/error/DuplicateDeclarationException.java b/src/core/src/tonkadur/fate/v1/error/DuplicateDeclarationException.java
index 066bbe6..eb42aba 100644
--- a/src/core/src/tonkadur/fate/v1/error/DuplicateDeclarationException.java
+++ b/src/core/src/tonkadur/fate/v1/error/DuplicateDeclarationException.java
@@ -33,7 +33,8 @@ public class DuplicateDeclarationException extends ParsingError
       final StringBuilder sb = new StringBuilder();
 
       sb.append(origin.get_context().toString());
-      sb.append("Declaration for ");
+      sb.append(error_category.toString());
+      sb.append(" Declaration for ");
       sb.append(original_declaration.get_type_name());
       sb.append(" '");
       sb.append(original_declaration.get_name());
diff --git a/src/core/src/tonkadur/fate/v1/error/ErrorCategory.java b/src/core/src/tonkadur/fate/v1/error/ErrorCategory.java
index ef1396e..35f4b94 100644
--- a/src/core/src/tonkadur/fate/v1/error/ErrorCategory.java
+++ b/src/core/src/tonkadur/fate/v1/error/ErrorCategory.java
@@ -2,21 +2,23 @@ package tonkadur.fate.v1.error;
 
 class ErrorCategory extends tonkadur.error.ErrorCategory
 {
+   public static final ErrorCategory CONFLICTING;
    public static final ErrorCategory DUPLICATE_DECLARATION;
-   public static final ErrorCategory CONFLICTING_DECLARATION;
+   public static final ErrorCategory INCOMPARABLE;
+   public static final ErrorCategory INCOMPATIBLE;
+   public static final ErrorCategory INVALID_USE;
    public static final ErrorCategory MISSING_DECLARATION;
-   public static final ErrorCategory UNKNOWN_SEQUENCE;
-   public static final ErrorCategory INCORRECT_TYPE;
-   public static final ErrorCategory INCOMPATIBLE_TYPE;
+   public static final ErrorCategory UNKNOWN;
 
    static
    {
+      CONFLICTING = new ErrorCategory("conflicting");
       DUPLICATE_DECLARATION = new ErrorCategory("duplicate_declaration");
-      CONFLICTING_DECLARATION = new ErrorCategory("conflicting_declaration");
+      INCOMPARABLE = new ErrorCategory("incomparable");
+      INCOMPATIBLE = new ErrorCategory("incompatible");
+      INVALID_USE = new ErrorCategory("invalid_use");
       MISSING_DECLARATION = new ErrorCategory("missing_declaration");
-      UNKNOWN_SEQUENCE = new ErrorCategory("unknown_sequence");
-      INCORRECT_TYPE = new ErrorCategory("incorrect_type");
-      INCOMPATIBLE_TYPE = new ErrorCategory("incompatible_type");
+      UNKNOWN = new ErrorCategory("unknown");
    }
 
    private ErrorCategory (final String name)
diff --git a/src/core/src/tonkadur/fate/v1/error/IncomparableDeclarationException.java b/src/core/src/tonkadur/fate/v1/error/IncomparableDeclarationException.java
new file mode 100644
index 0000000..c5dfc94
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/IncomparableDeclarationException.java
@@ -0,0 +1,65 @@
+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 IncomparableDeclarationException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final DeclaredEntity new_declaration;
+   protected final DeclaredEntity original_declaration;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public IncomparableDeclarationException
+   (
+      final DeclaredEntity new_declaration,
+      final DeclaredEntity original_declaration
+   )
+   {
+      super
+      (
+         ErrorLevel.ERROR,
+         ErrorCategory.INCOMPARABLE,
+         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(error_category.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 incomparable 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/IncomparableTypeException.java b/src/core/src/tonkadur/fate/v1/error/IncomparableTypeException.java
new file mode 100644
index 0000000..19ae9d6
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/IncomparableTypeException.java
@@ -0,0 +1,55 @@
+package tonkadur.fate.v1.error;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+import tonkadur.fate.v1.lang.Type;
+
+public class IncomparableTypeException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Type given_type;
+   protected final Type expected_type;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public IncomparableTypeException
+   (
+      final Origin call_origin,
+      final Type given_type,
+      final Type expected_type
+   )
+   {
+      super
+      (
+         ErrorLevel.ERROR,
+         ErrorCategory.INCOMPARABLE,
+         call_origin
+      );
+
+      this.given_type = given_type;
+      this.expected_type = expected_type;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.get_context().toString());
+      sb.append(error_category.toString());
+      sb.append(" Resulting type '");
+      sb.append(given_type.toString());
+      sb.append("' ");
+      sb.append(" is incomparable with the expected one ('");
+      sb.append(expected_type.toString());
+      sb.append("').");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/error/IncompatibleDeclarationException.java b/src/core/src/tonkadur/fate/v1/error/IncompatibleDeclarationException.java
index 582f593..f1f1be6 100644
--- a/src/core/src/tonkadur/fate/v1/error/IncompatibleDeclarationException.java
+++ b/src/core/src/tonkadur/fate/v1/error/IncompatibleDeclarationException.java
@@ -27,7 +27,7 @@ public class IncompatibleDeclarationException extends ParsingError
       super
       (
          ErrorLevel.ERROR,
-         ErrorCategory.CONFLICTING_DECLARATION,
+         ErrorCategory.INCOMPATIBLE,
          new_declaration.get_origin()
       );
 
@@ -41,7 +41,8 @@ public class IncompatibleDeclarationException extends ParsingError
       final StringBuilder sb = new StringBuilder();
 
       sb.append(origin.get_context().toString());
-      sb.append("Declaration for ");
+      sb.append(error_category.toString());
+      sb.append(" Declaration for ");
       sb.append(original_declaration.get_type_name());
       sb.append(" '");
       sb.append(original_declaration.get_name());
diff --git a/src/core/src/tonkadur/fate/v1/error/IncompatibleTypeException.java b/src/core/src/tonkadur/fate/v1/error/IncompatibleTypeException.java
new file mode 100644
index 0000000..da05cb9
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/IncompatibleTypeException.java
@@ -0,0 +1,55 @@
+package tonkadur.fate.v1.error;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+import tonkadur.fate.v1.lang.Type;
+
+public class IncompatibleTypeException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Type given_type;
+   protected final Type expected_type;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public IncompatibleTypeException
+   (
+      final Origin call_origin,
+      final Type given_type,
+      final Type expected_type
+   )
+   {
+      super
+      (
+         ErrorLevel.ERROR,
+         ErrorCategory.INCOMPATIBLE,
+         call_origin
+      );
+
+      this.given_type = given_type;
+      this.expected_type = expected_type;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.get_context().toString());
+      sb.append(error_category.toString());
+      sb.append(" Resulting type '");
+      sb.append(given_type.toString());
+      sb.append("' ");
+      sb.append(" is incompatible with the expected one ('");
+      sb.append(expected_type.toString());
+      sb.append("').");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/error/InvalidArityException.java b/src/core/src/tonkadur/fate/v1/error/InvalidArityException.java
new file mode 100644
index 0000000..578ce60
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/InvalidArityException.java
@@ -0,0 +1,52 @@
+package tonkadur.fate.v1.error;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+public class InvalidArityException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final int arity;
+   protected final int arguments_count;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public InvalidArityException
+   (
+      final Origin call_origin,
+      final int arguments_count,
+      final int arity
+   )
+   {
+      super
+      (
+         ErrorLevel.FATAL,
+         ErrorCategory.INVALID_USE,
+         call_origin
+      );
+
+      this.arguments_count = arguments_count;
+      this.arity = arity;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.get_context().toString());
+      sb.append(error_category.toString());
+      sb.append(" This supports a maximum or a minimum of ");
+      sb.append(arity);
+      sb.append(" parameter(s), but was given ");
+      sb.append(arguments_count);
+      sb.append(" of them.");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/error/InvalidTypeException.java b/src/core/src/tonkadur/fate/v1/error/InvalidTypeException.java
new file mode 100644
index 0000000..6a62edd
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/InvalidTypeException.java
@@ -0,0 +1,62 @@
+package tonkadur.fate.v1.error;
+
+import java.util.Collection;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+import tonkadur.fate.v1.lang.Type;
+
+public class InvalidTypeException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Type given_type;
+   protected final Collection<Type> allowed_types;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public InvalidTypeException
+   (
+      final Origin call_origin,
+      final Type given_type,
+      final Collection<Type> allowed_types
+   )
+   {
+      super
+      (
+         ErrorLevel.FATAL,
+         ErrorCategory.INVALID_USE,
+         call_origin
+      );
+
+      this.given_type = given_type;
+      this.allowed_types = allowed_types;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.get_context().toString());
+      sb.append(error_category.toString());
+      sb.append(" Type '");
+      sb.append(given_type.toString());
+      sb.append("' ");
+      sb.append(" is not useable here. The following base types are allowed:");
+
+      for (final Type allowed_type: allowed_types)
+      {
+         sb.append(System.lineSeparator());
+         sb.append("- ");
+         sb.append(allowed_types.toString());
+      }
+
+      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
index f564fbe..c4cb08f 100644
--- a/src/core/src/tonkadur/fate/v1/error/MissingDeclarationException.java
+++ b/src/core/src/tonkadur/fate/v1/error/MissingDeclarationException.java
@@ -34,7 +34,8 @@ public class MissingDeclarationException extends ParsingError
       final StringBuilder sb = new StringBuilder();
 
       sb.append(origin.get_context().toString());
-      sb.append("Unknown ");
+      sb.append(error_category.toString());
+      sb.append(" Unknown ");
       sb.append(type_name);
       sb.append(" '");
       sb.append(name);
diff --git a/src/core/src/tonkadur/fate/v1/lang/Event.java b/src/core/src/tonkadur/fate/v1/lang/Event.java
index 38b3210..b917ebf 100644
--- a/src/core/src/tonkadur/fate/v1/lang/Event.java
+++ b/src/core/src/tonkadur/fate/v1/lang/Event.java
@@ -70,6 +70,37 @@ public class Event extends DeclaredEntity
       return signature;
    }
 
+   @Override
+   public DeclaredEntity generate_comparable_to (final DeclaredEntity de)
+   {
+      final List<Type> new_signature;
+      final Event e;
+
+      if (!(de instanceof Event))
+      {
+         return ANY;
+      }
+
+      e = (Event) de;
+
+      if (signature.size() != e.signature.size())
+      {
+         return ANY;
+      }
+
+      new_signature =
+         new Merge<Type, Type, Type>()
+         {
+            @Override
+            protected Type lambda (final Type a, final Type b)
+            {
+               return (Type) a.generate_comparable_to(b);
+            }
+         }.merge(signature, e.signature);
+
+      return new Event(origin, new_signature, name);
+   }
+
    /**** Misc. ****************************************************************/
    @Override
    public boolean is_incompatible_with_declaration (final DeclaredEntity de)
@@ -90,10 +121,10 @@ public class Event extends DeclaredEntity
              */
             compatibility_result =
                (
-                  new Merge<Type,Type,Boolean>()
+                  new Merge<Type, Type, Boolean>()
                   {
                      @Override
-                     protected Boolean merge_fun (final Type a, final Type b)
+                     protected Boolean lambda (final Type a, final Type b)
                      {
                         return
                            new Boolean(a.is_incompatible_with_declaration(b));
diff --git a/src/core/src/tonkadur/fate/v1/lang/Operation.java b/src/core/src/tonkadur/fate/v1/lang/Operation.java
new file mode 100644
index 0000000..b193f5b
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/lang/Operation.java
@@ -0,0 +1,142 @@
+package tonkadur.fate.v1.lang;
+
+import java.util.Collection;
+import java.util.List;
+
+import tonkadur.error.ErrorManager;
+
+import tonkadur.parser.Origin;
+
+import tonkadur.fate.v1.error.ConflictingTypeException;
+import tonkadur.fate.v1.error.IncomparableTypeException;
+import tonkadur.fate.v1.error.IncompatibleTypeException;
+import tonkadur.fate.v1.error.InvalidArityException;
+import tonkadur.fate.v1.error.InvalidTypeException;
+
+import tonkadur.fate.v1.lang.meta.ValueNode;
+
+public class Operation extends ValueNode
+{
+   protected final Operator operator;
+   protected final List<ValueNode> operands;
+
+   protected Operation
+   (
+      final Origin origin,
+      final Type result_type,
+      final Operator operator,
+      final List<ValueNode> operands
+   )
+   {
+      super(origin, result_type);
+
+      this.operator = operator;
+      this.operands = operands;
+   }
+
+   public Operation build
+   (
+      final Origin origin,
+      final Operator operator,
+      final List<ValueNode> operands
+   )
+   throws
+      ConflictingTypeException,
+      IncomparableTypeException,
+      IncompatibleTypeException,
+      InvalidArityException,
+      InvalidTypeException
+   {
+      final Collection<Type> allowed_base_types;
+      final int operator_arity;
+      Type computed_type, previous_computed_type;
+
+      allowed_base_types = operator.get_allowed_base_types();
+      operator_arity = operator.get_arity();
+
+      if
+      (
+         (operator_arity != 0)
+         && (operator_arity < operands.size())
+      )
+      {
+         ErrorManager.handle
+         (
+            new InvalidArityException(origin, operands.size(), operator_arity)
+         );
+      }
+
+      computed_type = operands.get(0).get_type();
+
+      for (final ValueNode operand: operands)
+      {
+         final Type operand_type;
+
+         operand_type = operand.get_type();
+
+         if (!allowed_base_types.contains(operand_type.get_true_type()))
+         {
+            ErrorManager.handle
+            (
+               new InvalidTypeException
+               (
+                  operand.get_origin(),
+                  operand_type,
+                  allowed_base_types
+               )
+            );
+         }
+
+         if (computed_type.equals(operand_type))
+         {
+            continue;
+         }
+
+         ErrorManager.handle
+         (
+            new ConflictingTypeException
+            (
+               operand.get_origin(),
+               operand_type,
+               computed_type
+            )
+         );
+
+         if (operand_type.can_be_used_as(computed_type))
+         {
+            continue;
+         }
+
+         ErrorManager.handle
+         (
+            new IncompatibleTypeException
+            (
+               operand.get_origin(),
+               operand_type,
+               computed_type
+            )
+         );
+
+         previous_computed_type = computed_type;
+         computed_type =
+            (Type) computed_type.generate_comparable_to(operand_type);
+
+         if (computed_type.equals(Type.ANY))
+         {
+            ErrorManager.handle
+            (
+               new IncomparableTypeException
+               (
+                  operand.get_origin(),
+                  operand_type,
+                  previous_computed_type
+               )
+            );
+         }
+      }
+
+      computed_type = operator.transform_type(computed_type);
+
+      return new Operation(origin, computed_type, operator, operands);
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/lang/Operator.java b/src/core/src/tonkadur/fate/v1/lang/Operator.java
new file mode 100644
index 0000000..f8fb8ff
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/lang/Operator.java
@@ -0,0 +1,72 @@
+package tonkadur.fate.v1.lang;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashSet;
+
+public enum Operator
+{
+   PLUS("+", 0, Type.NUMBER_TYPES, null),
+   MINUS("-", 0, Type.NUMBER_TYPES, null),
+   TIMES("*", 0, Type.NUMBER_TYPES, null),
+   DIVIDED("/", 0, Type.NUMBER_TYPES, null),
+   POWER("^", 2, Type.NUMBER_TYPES, null),
+   RANDOM("rand", 2, (new Type[]{Type.INT}), null),
+
+   AND("and", 0, (new Type[]{Type.BOOLEAN}), null),
+   OR("or", 0, (new Type[]{Type.BOOLEAN}), null),
+   NOT("not", 1, (new Type[]{Type.BOOLEAN}), null),
+   IMPLIES("implies", 1, (new Type[]{Type.BOOLEAN}), null),
+
+   LOWER_THAN("<", 2, Type.NUMBER_TYPES, Type.BOOLEAN),
+   LOWER_EQUAL_THAN("=<", 2, Type.NUMBER_TYPES, Type.BOOLEAN),
+   GREATER_EQUAL_THAN(">=", 2, Type.NUMBER_TYPES, Type.BOOLEAN),
+   GREATER_THAN(">", 2, Type.NUMBER_TYPES, Type.BOOLEAN);
+
+   final private String name;
+   final private int arity;
+   final private Collection<Type> valid_input_types;
+   final private Type output_type_transform;
+
+   private Operator
+   (
+      final String name,
+      final int arity,
+      final Type[] valid_input_types,
+      final Type output_type_transform
+   )
+   {
+      this.name = name;
+      this.arity = arity;
+      this.valid_input_types =
+         new HashSet<Type>(Arrays.asList(valid_input_types));
+
+      this.output_type_transform = output_type_transform;
+   }
+
+   public Collection<Type> get_allowed_base_types ()
+   {
+      return valid_input_types;
+   }
+
+   public int get_arity ()
+   {
+      return arity;
+   }
+
+   public Type transform_type (final Type in)
+   {
+      if (output_type_transform == null)
+      {
+         return in;
+      }
+
+      return output_type_transform;
+   }
+
+   @Override
+   public String toString ()
+   {
+      return name;
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/lang/Type.java b/src/core/src/tonkadur/fate/v1/lang/Type.java
index 269e011..ad49268 100644
--- a/src/core/src/tonkadur/fate/v1/lang/Type.java
+++ b/src/core/src/tonkadur/fate/v1/lang/Type.java
@@ -1,5 +1,11 @@
 package tonkadur.fate.v1.lang;
 
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+
 import tonkadur.parser.Context;
 import tonkadur.parser.Location;
 import tonkadur.parser.Origin;
@@ -8,21 +14,37 @@ import tonkadur.fate.v1.lang.meta.DeclaredEntity;
 
 public class Type extends DeclaredEntity
 {
-   protected static final Type ANY;
+   public static final Type ANY;
+   public static final Type BOOLEAN;
+   public static final Type DICT;
+   public static final Type FLOAT;
+   public static final Type INT;
+   public static final Type LIST;
+   public static final Type SET;
+   public static final Type STRING;
+
+   public static final Type[] NUMBER_TYPES;
 
    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"
-         );
+      final Origin base;
+
+      base = new Origin(new Context(""), Location.BASE_LANGUAGE);
+
+      /*
+       * Use of a space necessary to avoid conflicting with a user created type.
+       */
+      ANY = new Type(base, null, "undetermined type");
+
+      BOOLEAN = new Type(base, null, "boolean");
+      DICT = new Type(base, null, "dict");
+      FLOAT = new Type(base, null, "float");
+      INT = new Type(base, null, "int");
+      LIST = new Type(base, null, "list");
+      SET = new Type(base, null, "set");
+      STRING = new Type(base, null, "string");
+
+      NUMBER_TYPES = new Type[]{FLOAT, INT};
    }
 
    public static Type value_on_missing ()
@@ -36,6 +58,7 @@ public class Type extends DeclaredEntity
       return "Type";
    }
 
+
    /***************************************************************************/
    /**** MEMBERS **************************************************************/
    /***************************************************************************/
@@ -69,7 +92,6 @@ public class Type extends DeclaredEntity
    }
 
    /**** Accessors ************************************************************/
-
    public Type get_true_type ()
    {
       return true_type;
@@ -91,6 +113,44 @@ public class Type extends DeclaredEntity
       return this_or_parent_equals(t);
    }
 
+   /*
+    * This is for the very special case where a type is used despite not being
+    * even a sub-type of the expected one. Using this rather expensive function,
+    * the most restrictive shared type will be returned. If no such type exists,
+    * the ANY time is returned.
+    */
+   @Override
+   public DeclaredEntity generate_comparable_to (final DeclaredEntity de)
+   {
+      final Iterator<Type> it0, it1;
+      Type result, candidate;
+
+      if (!(de instanceof Type))
+      {
+         return ANY;
+      }
+
+      it0 = ((Type) de).compute_full_type_chain().iterator();
+      it1 = compute_full_type_chain().iterator();
+
+      result = Type.ANY;
+
+      while (it0.hasNext() && it1.hasNext())
+      {
+         candidate = it0.next();
+
+         if (!candidate.name.equals(it1.next().name))
+         {
+            break;
+         }
+
+         result = candidate;
+      }
+
+      return result;
+   }
+
+
    /**** Misc. ****************************************************************/
    @Override
    public boolean is_incompatible_with_declaration (final DeclaredEntity de)
@@ -144,4 +204,25 @@ public class Type extends DeclaredEntity
 
       return parent.this_or_parent_equals(t);
    }
+
+   protected List<Type> compute_full_type_chain ()
+   {
+      final List<Type> result;
+      Type t;
+
+      result = new ArrayList<Type>();
+
+      t = this;
+
+      while (t != null)
+      {
+         result.add(t);
+
+         t = t.parent;
+      }
+
+      Collections.reverse(result);
+
+      return result;
+   }
 }
diff --git a/src/core/src/tonkadur/fate/v1/lang/World.java b/src/core/src/tonkadur/fate/v1/lang/World.java
index e6bf2d6..5db6d16 100644
--- a/src/core/src/tonkadur/fate/v1/lang/World.java
+++ b/src/core/src/tonkadur/fate/v1/lang/World.java
@@ -78,18 +78,16 @@ public class World
    /***************************************************************************/
    protected void add_base_types ()
    {
-      final Origin base;
-
-      base = new Origin(new Context(""), Location.BASE_LANGUAGE);
 
       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"));
+         type_collection.add(Type.BOOLEAN);
+         type_collection.add(Type.DICT);
+         type_collection.add(Type.FLOAT);
+         type_collection.add(Type.INT);
+         type_collection.add(Type.LIST);
+         type_collection.add(Type.SET);
+         type_collection.add(Type.STRING);
       }
       catch (final Throwable t)
       {
diff --git a/src/core/src/tonkadur/fate/v1/lang/meta/DeclarationCollection.java b/src/core/src/tonkadur/fate/v1/lang/meta/DeclarationCollection.java
index 838d109..7bcaaa1 100644
--- a/src/core/src/tonkadur/fate/v1/lang/meta/DeclarationCollection.java
+++ b/src/core/src/tonkadur/fate/v1/lang/meta/DeclarationCollection.java
@@ -12,18 +12,28 @@ import tonkadur.fate.v1.error.MissingDeclarationException;
 import tonkadur.fate.v1.error.DuplicateDeclarationException;
 import tonkadur.fate.v1.error.ConflictingDeclarationException;
 import tonkadur.fate.v1.error.IncompatibleDeclarationException;
+import tonkadur.fate.v1.error.IncomparableDeclarationException;
 
 public class DeclarationCollection <Declared extends DeclaredEntity>
 {
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
    protected final Map<String, Declared> collection;
    protected final Declared value_on_missing;
 
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+
+   /**** Constructors *********************************************************/
    public DeclarationCollection (final Declared value_on_missing)
    {
       collection = new HashMap<String, Declared>();
       this.value_on_missing = value_on_missing;
    }
 
+   /**** Accessors ************************************************************/
    public Collection<Declared> get_all ()
    {
       return collection.values();
@@ -34,13 +44,14 @@ public class DeclarationCollection <Declared extends DeclaredEntity>
       return collection.containsKey(name);
    }
 
-   public void add (final Declared entity)
+   public void add (Declared entity)
    throws
       DuplicateDeclarationException,
       ConflictingDeclarationException,
-      IncompatibleDeclarationException
+      IncompatibleDeclarationException,
+      IncomparableDeclarationException
    {
-      assert_entity_can_be_added(entity);
+      entity = assert_entity_can_be_added(entity);
       collection.put(entity.get_name(), entity);
    }
 
@@ -72,19 +83,21 @@ public class DeclarationCollection <Declared extends DeclaredEntity>
    /***************************************************************************/
    /**** PROTECTED ************************************************************/
    /***************************************************************************/
-   protected void assert_entity_can_be_added (final Declared new_version)
+   protected Declared assert_entity_can_be_added (Declared new_version)
    throws
       DuplicateDeclarationException,
       ConflictingDeclarationException,
-      IncompatibleDeclarationException
+      IncompatibleDeclarationException,
+      IncomparableDeclarationException
    {
+      final DeclaredEntity de;
       final Declared previous_version;
 
       previous_version = collection.get(new_version.get_name());
 
       if (previous_version == null)
       {
-         return;
+         return new_version;
       }
 
       ErrorManager.handle
@@ -98,7 +111,7 @@ public class DeclarationCollection <Declared extends DeclaredEntity>
 
       if (!previous_version.conflicts_with_declaration(new_version))
       {
-         return;
+         return new_version;
       }
 
       ErrorManager.handle
@@ -108,12 +121,35 @@ public class DeclarationCollection <Declared extends DeclaredEntity>
 
       if (!previous_version.is_incompatible_with_declaration(new_version))
       {
-         return;
+         return new_version;
       }
 
       ErrorManager.handle
       (
          new IncompatibleDeclarationException(new_version, previous_version)
       );
+
+      de = new_version.generate_comparable_to(previous_version);
+
+      try
+      {
+         new_version = (Declared) de;
+      }
+      catch (final ClassCastException e)
+      {
+         e.printStackTrace();
+
+         System.exit(-1);
+      }
+
+      if (new_version.equals(value_on_missing))
+      {
+         ErrorManager.handle
+         (
+            new IncomparableDeclarationException(new_version, previous_version)
+         );
+      }
+
+      return new_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
index 5748391..2e08cf7 100644
--- a/src/core/src/tonkadur/fate/v1/lang/meta/DeclaredEntity.java
+++ b/src/core/src/tonkadur/fate/v1/lang/meta/DeclaredEntity.java
@@ -49,6 +49,7 @@ public abstract class DeclaredEntity
       return origin;
    }
 
+   /**** Compatibility ********************************************************/
    public boolean conflicts_with_declaration (final DeclaredEntity de)
    {
       return !equals(de);
@@ -59,6 +60,13 @@ public abstract class DeclaredEntity
       return !equals(de);
    }
 
+   public <ThisType extends DeclaredEntity>
+   ThisType generate_comparable_to (final ThisType de)
+   {
+      return null;
+   }
+
+   /**** Misc. ****************************************************************/
    @Override
    public boolean equals (final Object o)
    {
diff --git a/src/core/src/tonkadur/fate/v1/lang/meta/InstructionNode.java b/src/core/src/tonkadur/fate/v1/lang/meta/InstructionNode.java
new file mode 100644
index 0000000..3587152
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/lang/meta/InstructionNode.java
@@ -0,0 +1,60 @@
+package tonkadur.fate.v1.lang.meta;
+
+import java.util.Collection;
+import java.util.HashSet;
+
+import tonkadur.parser.Origin;
+
+public abstract class InstructionNode extends Node
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Collection<InstructionNode> parents;
+   protected InstructionNode child;
+
+   /***************************************************************************/
+   /**** PROTECTED ************************************************************/
+   /***************************************************************************/
+   /**** Constructors *********************************************************/
+   protected InstructionNode (final Origin origin)
+   {
+      super(origin);
+
+      parents = new HashSet<InstructionNode>();
+      child = null;
+   }
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   /**** Accessors ************************************************************/
+   public void link_parent (final InstructionNode parent)
+   {
+      parent.child = this;
+
+      parents.add(parent);
+   }
+
+   public Collection<InstructionNode> get_parents ()
+   {
+      return parents;
+   }
+
+   public InstructionNode get_child ()
+   {
+      return child;
+   }
+
+   /**** Misc. ****************************************************************/
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.toString());
+      sb.append("(Instruction)");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/lang/meta/Node.java b/src/core/src/tonkadur/fate/v1/lang/meta/Node.java
new file mode 100644
index 0000000..e5317d9
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/lang/meta/Node.java
@@ -0,0 +1,62 @@
+package tonkadur.fate.v1.lang.meta;
+
+import tonkadur.parser.Origin;
+
+public abstract class Node
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Origin origin;
+
+   /***************************************************************************/
+   /**** PROTECTED ************************************************************/
+   /***************************************************************************/
+   /**** Constructors *********************************************************/
+   protected Node (final Origin origin)
+   {
+      this.origin = origin;
+   }
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   /**** Accessors ************************************************************/
+   public Origin get_origin ()
+   {
+      return origin;
+   }
+
+   /**** Misc. ****************************************************************/
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.toString());
+      sb.append("(Node)");
+
+      return sb.toString();
+   }
+
+   @Override
+   public boolean equals (final Object o)
+   {
+      if (o instanceof Node)
+      {
+         final Node in;
+
+         in = (Node) o;
+
+         return toString().equals(in.toString());
+      }
+
+      return false;
+   }
+
+   @Override
+   public int hashCode ()
+   {
+      return toString().hashCode();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/lang/meta/ValueNode.java b/src/core/src/tonkadur/fate/v1/lang/meta/ValueNode.java
new file mode 100644
index 0000000..6670855
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/lang/meta/ValueNode.java
@@ -0,0 +1,47 @@
+package tonkadur.fate.v1.lang.meta;
+
+import tonkadur.parser.Origin;
+
+import tonkadur.fate.v1.lang.Type;
+
+public abstract class ValueNode extends Node
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Type type;
+
+   /***************************************************************************/
+   /**** PROTECTED ************************************************************/
+   /***************************************************************************/
+   /**** Constructors *********************************************************/
+   protected ValueNode (final Origin origin, final Type type)
+   {
+      super(origin);
+
+      this.type = type;
+   }
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   /**** Accessors ************************************************************/
+   public Type get_type ()
+   {
+      return type;
+   }
+
+   /**** Misc. ****************************************************************/
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.toString());
+      sb.append("(");
+      sb.append(type.get_name());
+      sb.append(" Value Node)");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/functional/Merge.java b/src/core/src/tonkadur/functional/Merge.java
index 68bb0e7..29d37c5 100644
--- a/src/core/src/tonkadur/functional/Merge.java
+++ b/src/core/src/tonkadur/functional/Merge.java
@@ -28,7 +28,7 @@ public class Merge <Input0, Input1, Output>
       {
          output.add
          (
-            merge_fun
+            lambda
             (
                it0.hasNext() ? it0.next() : null,
                it1.hasNext() ? it1.next() : null
@@ -39,7 +39,7 @@ public class Merge <Input0, Input1, Output>
       return output;
    }
 
-   protected Output merge_fun (final Input0 i0, final Input1 i1)
+   protected Output lambda (final Input0 i0, final Input1 i1)
    {
       return null;
    }