Resolving a lot of TODOs.

22 files changed, 366 insertions, 75 deletions

diff --git a/src/core/src/tonkadur/error/BasicError.java b/src/core/src/tonkadur/error/BasicError.java
new file mode 100644
index 0000000..9c0f01d
--- /dev/null
+++ b/src/core/src/tonkadur/error/BasicError.java
@@ -0,0 +1,37 @@
+package tonkadur.error;
+
+public class BasicError extends tonkadur.error.Error
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final String description;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public BasicError
+   (
+      final ErrorLevel error_level,
+      final ErrorCategory error_category,
+      final String description
+   )
+   {
+      super(error_level, error_category);
+
+      this.description = description;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(error_level.toString());
+      sb.append(error_category.toString());
+      sb.append(System.lineSeparator());
+      sb.append(description);
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/error/InvalidTypeArityException.java b/src/core/src/tonkadur/fate/v1/error/InvalidTypeArityException.java
new file mode 100644
index 0000000..417eb79
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/InvalidTypeArityException.java
@@ -0,0 +1,54 @@
+package tonkadur.fate.v1.error;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+import tonkadur.fate.v1.lang.type.Type;
+
+public class InvalidTypeArityException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Type base_type;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public InvalidTypeArityException
+   (
+      final Origin call_origin,
+      final Type base_type
+   )
+   {
+      super
+      (
+         ErrorLevel.FATAL,
+         ErrorCategory.INVALID_USE,
+         call_origin
+      );
+
+      this.base_type = base_type;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.toString());
+      sb.append(" ");
+      sb.append(error_category.toString());
+      sb.append(System.lineSeparator());
+
+      sb.append("Type ");
+      sb.append(base_type.toString());
+      sb.append(" takes ");
+      sb.append(base_type.get_parameters().size());
+      sb.append(" type(s) as parameter(s).");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/error/NotAReferenceException.java b/src/core/src/tonkadur/fate/v1/error/NotAReferenceException.java
new file mode 100644
index 0000000..396b4fd
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/NotAReferenceException.java
@@ -0,0 +1,53 @@
+package tonkadur.fate.v1.error;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+import tonkadur.fate.v1.lang.meta.Computation;
+
+public class NotAReferenceException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Computation computation;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public NotAReferenceException
+   (
+      final Computation computation
+   )
+   {
+      super
+      (
+         ErrorLevel.WARNING,
+         ErrorCategory.INVALID_USE,
+         computation.get_origin()
+      );
+
+      this.computation = computation;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.toString());
+      sb.append(" ");
+      sb.append(error_category.toString());
+      sb.append(System.lineSeparator());
+
+      sb.append("The computation ");
+      sb.append(computation.toString());
+      sb.append(" is being used as a reference, but isn't one.");
+      sb.append(" The instruction using it will not be able to modify the");
+      sb.append(" memory you thought was targeted by this computation.");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/lang/Sequence.java b/src/core/src/tonkadur/fate/v1/lang/Sequence.java
index 5356cba..0b903c6 100644
--- a/src/core/src/tonkadur/fate/v1/lang/Sequence.java
+++ b/src/core/src/tonkadur/fate/v1/lang/Sequence.java
@@ -82,7 +82,7 @@ public class Sequence extends DeclaredEntity
       return null;
    }
 
-   public boolean assert_can_take_parameters
+   public boolean propagate_expected_types_and_assert_can_take_parameters
    (
       final Origin origin,
       final List<Computation> parameters
diff --git a/src/core/src/tonkadur/fate/v1/lang/World.java b/src/core/src/tonkadur/fate/v1/lang/World.java
index bc85e83..8355a2e 100644
--- a/src/core/src/tonkadur/fate/v1/lang/World.java
+++ b/src/core/src/tonkadur/fate/v1/lang/World.java
@@ -391,7 +391,11 @@ public class World
             {
                if
                (
-                  !seq.assert_can_take_parameters(use.get_car(), use.get_cdr())
+                  !seq.propagate_expected_types_and_assert_can_take_parameters
+                  (
+                     use.get_car(),
+                     use.get_cdr()
+                  )
                )
                {
                   is_sane = false;
diff --git a/src/core/src/tonkadur/fate/v1/lang/computation/FieldAccess.java b/src/core/src/tonkadur/fate/v1/lang/computation/FieldAccess.java
index d48c997..dc9cea7 100644
--- a/src/core/src/tonkadur/fate/v1/lang/computation/FieldAccess.java
+++ b/src/core/src/tonkadur/fate/v1/lang/computation/FieldAccess.java
@@ -85,7 +85,7 @@ public class FieldAccess extends Computation
             (
                origin,
                current_type,
-               Collections.singleton(Type.ANY), // FIXME: Type.STRUCT
+               Collections.singleton(Type.ANY), // TODO: add StructType.ARCHETYPE
                parent.toString()
             )
          );
diff --git a/src/core/src/tonkadur/fate/v1/lang/computation/GenericComputation.java b/src/core/src/tonkadur/fate/v1/lang/computation/GenericComputation.java
index d2a5ef0..4f50166 100644
--- a/src/core/src/tonkadur/fate/v1/lang/computation/GenericComputation.java
+++ b/src/core/src/tonkadur/fate/v1/lang/computation/GenericComputation.java
@@ -5,7 +5,13 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
+import tonkadur.error.BasicError;
+import tonkadur.error.ErrorCategory;
+import tonkadur.error.ErrorLevel;
+import tonkadur.error.ErrorManager;
+
 import tonkadur.parser.Origin;
+import tonkadur.parser.BasicParsingError;
 
 import tonkadur.functional.Cons;
 
@@ -45,16 +51,22 @@ public abstract class GenericComputation extends Computation
 
             if (previous_entry != null)
             {
-               // TODO Exception handling.
-               throw new Exception
+               ErrorManager.handle
                (
-                  "[F] Unable to add alias for Generic Fate Computation '"
-                  + alias
-                  + "' from class '"
-                  + c.getName()
-                  + "': it has already been claimed by class '"
-                  + previous_entry.getName()
-                  + "'."
+                  new BasicError
+                  (
+                     ErrorLevel.FATAL,
+                     ErrorCategory.PROGRAMMING_ERROR,
+                     (
+                        "Unable to add alias for Generic Fate Computation '"
+                        + alias
+                        + "' from class '"
+                        + c.getName()
+                        + "': it has already been claimed by class '"
+                        + previous_entry.getName()
+                        + "'."
+                     )
+                  )
                );
             }
 
@@ -88,16 +100,16 @@ public abstract class GenericComputation extends Computation
 
       if (computation_class == null)
       {
-         // TODO use a separate class for this.
-         throw
-            new Exception
+         ErrorManager.handle
+         (
+            new BasicParsingError
             (
-               "[E] Unknown Generic Fate Computation '"
-               + name
-               + "' at "
-               + origin
-               + "."
-            );
+               ErrorLevel.ERROR,
+               tonkadur.fate.v1.error.ErrorCategory.UNKNOWN,
+               origin,
+               ("Unknown Generic Fate Computation '" + name + "'.")
+            )
+         );
       }
 
       return
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/GenericInstruction.java b/src/core/src/tonkadur/fate/v1/lang/instruction/GenericInstruction.java
index 065c7db..8c2b77e 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/GenericInstruction.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/GenericInstruction.java
@@ -5,7 +5,13 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
+import tonkadur.error.BasicError;
+import tonkadur.error.ErrorCategory;
+import tonkadur.error.ErrorLevel;
+import tonkadur.error.ErrorManager;
+
 import tonkadur.parser.Origin;
+import tonkadur.parser.BasicParsingError;
 
 import tonkadur.functional.Cons;
 
@@ -46,16 +52,22 @@ public abstract class GenericInstruction extends Instruction
 
             if (previous_entry != null)
             {
-               // TODO Exception handling.
-               throw new Exception
+               ErrorManager.handle
                (
-                  "[F] Unable to add alias for Generic Fate Instruction '"
-                  + alias
-                  + "' from class '"
-                  + c.getName()
-                  + "': it has already been claimed by class '"
-                  + previous_entry.getName()
-                  + "'."
+                  new BasicError
+                  (
+                     ErrorLevel.FATAL,
+                     ErrorCategory.PROGRAMMING_ERROR,
+                     (
+                        "Unable to add alias for Generic Fate Instruction '"
+                        + alias
+                        + "' from class '"
+                        + c.getName()
+                        + "': it has already been claimed by class '"
+                        + previous_entry.getName()
+                        + "'."
+                     )
+                  )
                );
             }
 
@@ -89,16 +101,16 @@ public abstract class GenericInstruction extends Instruction
 
       if (computation_class == null)
       {
-         // TODO use a separate class for this.
-         throw
-            new Exception
+         ErrorManager.handle
+         (
+            new BasicParsingError
             (
-               "[E] Unknown Generic Fate Instruction '"
-               + name
-               + "' at "
-               + origin
-               + "."
-            );
+               ErrorLevel.ERROR,
+               tonkadur.fate.v1.error.ErrorCategory.UNKNOWN,
+               origin,
+               ("Unknown Generic Fate Instruction '" + name + "'.")
+            )
+         );
       }
 
       return
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/SequenceCall.java b/src/core/src/tonkadur/fate/v1/lang/instruction/SequenceCall.java
index 2972417..43e56e6 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/SequenceCall.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/SequenceCall.java
@@ -55,7 +55,6 @@ public class SequenceCall extends Instruction
       return parameters;
    }
 
-   // TODO: call this at some point.
    public void perform_signature_checks (final List<Type> signature)
    throws ParsingError
    {
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/SequenceJump.java b/src/core/src/tonkadur/fate/v1/lang/instruction/SequenceJump.java
index f7157ff..5b85568 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/SequenceJump.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/SequenceJump.java
@@ -38,7 +38,6 @@ public class SequenceJump extends Instruction
    }
 
    /**** Accessors ************************************************************/
-   // TODO: call this at some point.
    public void perform_signature_checks (final List<Type> signature)
    throws ParsingError
    {
diff --git a/src/core/src/tonkadur/fate/v1/lang/meta/Computation.java b/src/core/src/tonkadur/fate/v1/lang/meta/Computation.java
index 62d88ed..173ad53 100644
--- a/src/core/src/tonkadur/fate/v1/lang/meta/Computation.java
+++ b/src/core/src/tonkadur/fate/v1/lang/meta/Computation.java
@@ -1,8 +1,12 @@
 package tonkadur.fate.v1.lang.meta;
 
+import tonkadur.error.ErrorManager;
+
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
+import tonkadur.fate.v1.error.NotAReferenceException;
+
 import tonkadur.fate.v1.lang.type.Type;
 import tonkadur.fate.v1.lang.type.FutureType;
 
@@ -57,14 +61,9 @@ public abstract class Computation extends Node
    public void use_as_reference ()
    throws ParsingError
    {
-      // TODO: proper ParsingError.
-      System.err.println
+      ErrorManager.handle
       (
-         "[W] Computation at "
-         + origin.toString()
-         + " is being used as a reference, but isn't one. The instruction will"
-         + " not be able to modify the memory you thought was targeted by this"
-         + " computation."
+         new NotAReferenceException(this)
       );
    }
 
diff --git a/src/core/src/tonkadur/fate/v1/lang/meta/VariableFromWord.java b/src/core/src/tonkadur/fate/v1/lang/meta/VariableFromWord.java
index 8fa713d..813cef4 100644
--- a/src/core/src/tonkadur/fate/v1/lang/meta/VariableFromWord.java
+++ b/src/core/src/tonkadur/fate/v1/lang/meta/VariableFromWord.java
@@ -7,10 +7,17 @@ import java.util.Arrays;
 import java.util.List;
 import java.util.ArrayList;
 
+import tonkadur.error.ErrorLevel;
+import tonkadur.error.ErrorManager;
+
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
+import tonkadur.parser.BasicParsingError;
+
+import tonkadur.fate.v1.error.ErrorCategory;
 
 import tonkadur.fate.v1.parser.ParserData;
+
 import tonkadur.fate.v1.lang.Variable;
 
 import tonkadur.fate.v1.lang.computation.Constant;
@@ -109,10 +116,21 @@ public class VariableFromWord
             }
             else
             {
-               /* TODO: error */
-               System.err.println("Unimplemented error in VariableFromWord.");
-
-               System.exit(-1);
+               ErrorManager.handle
+               (
+                  new BasicParsingError
+                  (
+                     ErrorLevel.ERROR,
+                     ErrorCategory.INVALID_USE,
+                     origin.with_hint(subref),
+                     (
+                        "Attempting to access a subreference from a value of"
+                        + " type "
+                        + t.toString()
+                        + ", despite this type not being useable in this way."
+                     )
+                  )
+               );
             }
          }
       }
diff --git a/src/core/src/tonkadur/fate/v1/lang/type/CollectionType.java b/src/core/src/tonkadur/fate/v1/lang/type/CollectionType.java
index c3ffb35..e563be2 100644
--- a/src/core/src/tonkadur/fate/v1/lang/type/CollectionType.java
+++ b/src/core/src/tonkadur/fate/v1/lang/type/CollectionType.java
@@ -4,11 +4,12 @@ import java.util.List;
 import java.util.Collections;
 
 import tonkadur.error.ErrorManager;
-import tonkadur.parser.ParsingError;
 
+import tonkadur.parser.ParsingError;
 import tonkadur.parser.Origin;
 
 import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.fate.v1.error.InvalidTypeArityException;
 
 import tonkadur.fate.v1.lang.meta.DeclaredEntity;
 
@@ -223,7 +224,7 @@ public class CollectionType extends Type
    {
       if (this.parameters.size() != parameters.size())
       {
-         // TODO: error;
+         ErrorManager.handle(new InvalidTypeArityException(origin, this));
       }
 
       return new CollectionType(origin, parameters.get(0), is_set, name);
diff --git a/src/core/src/tonkadur/fate/v1/lang/type/ConsType.java b/src/core/src/tonkadur/fate/v1/lang/type/ConsType.java
index 6430494..be3d60d 100644
--- a/src/core/src/tonkadur/fate/v1/lang/type/ConsType.java
+++ b/src/core/src/tonkadur/fate/v1/lang/type/ConsType.java
@@ -3,8 +3,12 @@ package tonkadur.fate.v1.lang.type;
 import java.util.Arrays;
 import java.util.List;
 
+import tonkadur.error.ErrorManager;
+
 import tonkadur.parser.Origin;
 
+import tonkadur.fate.v1.error.InvalidTypeArityException;
+
 import tonkadur.fate.v1.lang.meta.DeclaredEntity;
 
 public class ConsType extends Type
@@ -50,7 +54,7 @@ public class ConsType extends Type
    {
       if (this.parameters.size() != parameters.size())
       {
-         // TODO: error;
+         ErrorManager.handle(new InvalidTypeArityException(origin, this));
       }
 
       return new ConsType(origin, parameters.get(0), parameters.get(1), name);
diff --git a/src/core/src/tonkadur/fate/v1/lang/type/DictionaryType.java b/src/core/src/tonkadur/fate/v1/lang/type/DictionaryType.java
index b4d227f..9755e36 100644
--- a/src/core/src/tonkadur/fate/v1/lang/type/DictionaryType.java
+++ b/src/core/src/tonkadur/fate/v1/lang/type/DictionaryType.java
@@ -4,11 +4,12 @@ import java.util.List;
 import java.util.Arrays;
 
 import tonkadur.error.ErrorManager;
-import tonkadur.parser.ParsingError;
 
+import tonkadur.parser.ParsingError;
 import tonkadur.parser.Origin;
 
 import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.fate.v1.error.InvalidTypeArityException;
 
 import tonkadur.fate.v1.lang.meta.DeclaredEntity;
 
@@ -191,7 +192,7 @@ public class DictionaryType extends Type
    {
       if (this.parameters.size() != parameters.size())
       {
-         // TODO: error;
+         ErrorManager.handle(new InvalidTypeArityException(origin, this));
       }
 
       return
diff --git a/src/core/src/tonkadur/fate/v1/lang/type/ExtraType.java b/src/core/src/tonkadur/fate/v1/lang/type/ExtraType.java
index 919abd6..151cb98 100644
--- a/src/core/src/tonkadur/fate/v1/lang/type/ExtraType.java
+++ b/src/core/src/tonkadur/fate/v1/lang/type/ExtraType.java
@@ -4,8 +4,12 @@ import java.util.List;
 import java.util.HashMap;
 import java.util.Map;
 
+import tonkadur.error.ErrorManager;
+
 import tonkadur.parser.Origin;
 
+import tonkadur.fate.v1.error.InvalidTypeArityException;
+
 import tonkadur.fate.v1.lang.meta.DeclaredEntity;
 import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
@@ -37,7 +41,7 @@ public class ExtraType extends Type
    {
       if (this.parameters.size() != parameters.size())
       {
-         // TODO: error;
+         ErrorManager.handle(new InvalidTypeArityException(origin, this));
       }
 
       return new ExtraType(origin, this, name, parameters);
diff --git a/src/core/src/tonkadur/fate/v1/lang/type/FutureType.java b/src/core/src/tonkadur/fate/v1/lang/type/FutureType.java
index f85053d..ca9bd5a 100644
--- a/src/core/src/tonkadur/fate/v1/lang/type/FutureType.java
+++ b/src/core/src/tonkadur/fate/v1/lang/type/FutureType.java
@@ -6,11 +6,15 @@ import java.util.Collection;
 import java.util.Collections;
 
 import tonkadur.error.ErrorManager;
+import tonkadur.error.BasicError;
+import tonkadur.error.ErrorLevel;
 
 import tonkadur.parser.Context;
 import tonkadur.parser.Location;
 import tonkadur.parser.Origin;
 
+import tonkadur.fate.v1.error.ErrorCategory;
+
 import tonkadur.fate.v1.lang.meta.DeclaredEntity;
 
 public class FutureType extends Type
@@ -31,16 +35,28 @@ public class FutureType extends Type
    {
       if (resolved_type == null)
       {
-         // TODO: proper error handling
-         //
-         System.err.println
-         (
-            "[F] Future Type from "
-            + get_origin().toString()
-            + " used prior to resolution."
-         );
-
-         System.exit(-1);
+         try
+         {
+            ErrorManager.handle
+            (
+               new BasicError
+               (
+                  ErrorLevel.FATAL,
+                  ErrorCategory.MISSING_DECLARATION,
+                  (
+                     "Future Type from "
+                     + get_origin().toString()
+                     + " used prior to resolution."
+                  )
+               )
+            );
+         }
+         catch (final Throwable t)
+         {
+            t.printStackTrace();
+            System.err.println(t.toString());
+            System.exit(-1);
+         }
       }
    }
 
diff --git a/src/core/src/tonkadur/fate/v1/lang/type/PointerType.java b/src/core/src/tonkadur/fate/v1/lang/type/PointerType.java
index daf5bc8..a3e25ae 100644
--- a/src/core/src/tonkadur/fate/v1/lang/type/PointerType.java
+++ b/src/core/src/tonkadur/fate/v1/lang/type/PointerType.java
@@ -3,8 +3,12 @@ package tonkadur.fate.v1.lang.type;
 import java.util.Collections;
 import java.util.List;
 
+import tonkadur.error.ErrorManager;
+
 import tonkadur.parser.Origin;
 
+import tonkadur.fate.v1.error.InvalidTypeArityException;
+
 import tonkadur.fate.v1.lang.meta.DeclaredEntity;
 
 public class PointerType extends Type
@@ -133,7 +137,7 @@ public class PointerType extends Type
    {
       if (this.parameters.size() != 1)
       {
-         // TODO: error;
+         ErrorManager.handle(new InvalidTypeArityException(origin, this));
       }
 
       return new PointerType(origin, parameters.get(0), "auto gen");
diff --git a/src/core/src/tonkadur/fate/v1/lang/type/Type.java b/src/core/src/tonkadur/fate/v1/lang/type/Type.java
index 1bed5da..bb1ec71 100644
--- a/src/core/src/tonkadur/fate/v1/lang/type/Type.java
+++ b/src/core/src/tonkadur/fate/v1/lang/type/Type.java
@@ -14,6 +14,7 @@ import tonkadur.parser.Location;
 import tonkadur.parser.Origin;
 
 import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.fate.v1.error.InvalidTypeArityException;
 
 import tonkadur.fate.v1.lang.meta.DeclaredEntity;
 
@@ -262,7 +263,7 @@ public class Type extends DeclaredEntity
    {
       if (this.parameters.size() != parameters.size())
       {
-         // TODO: error;
+         ErrorManager.handle(new InvalidTypeArityException(origin, this));
       }
 
       return new Type(origin, get_base_type(), name, parameters);
diff --git a/src/core/src/tonkadur/fate/v1/parser/FateLexer.g4 b/src/core/src/tonkadur/fate/v1/parser/FateLexer.g4
index ca632dd..95a614c 100644
--- a/src/core/src/tonkadur/fate/v1/parser/FateLexer.g4
+++ b/src/core/src/tonkadur/fate/v1/parser/FateLexer.g4
@@ -94,7 +94,6 @@ FOR_EACH_KW: L_PAREN 'for'US'each' SEP+;
 WHILE_KW: L_PAREN 'while' SEP+;
 SWITCH_KW: L_PAREN 'switch' SEP+;
 
-// FIXME: this hides generic if_else and if.
 IF_ELSE_KW: L_PAREN 'if'US'else' SEP+;
 IF_KW: L_PAREN 'if' SEP+;
 
diff --git a/src/core/src/tonkadur/fate/v1/parser/FateParser.g4 b/src/core/src/tonkadur/fate/v1/parser/FateParser.g4
index aded279..71d1d36 100644
--- a/src/core/src/tonkadur/fate/v1/parser/FateParser.g4
+++ b/src/core/src/tonkadur/fate/v1/parser/FateParser.g4
@@ -19,6 +19,8 @@ options
 
    import tonkadur.Files;
 
+   import tonkadur.error.ErrorLevel;
+   import tonkadur.error.ErrorCategory;
    import tonkadur.error.ErrorManager;
 
    import tonkadur.functional.Cons;
@@ -26,6 +28,7 @@ options
    import tonkadur.parser.Context;
    import tonkadur.parser.Location;
    import tonkadur.parser.Origin;
+   import tonkadur.parser.BasicParsingError;
 
 /* Conflicts with an existing package */
 /*   import tonkadur.fate.v1.tonkadur.fate.v1.Utils; */
@@ -34,6 +37,7 @@ options
    import tonkadur.fate.v1.error.IllegalReferenceNameException;
    import tonkadur.fate.v1.error.InvalidArityException;
    import tonkadur.fate.v1.error.InvalidTypeException;
+   import tonkadur.fate.v1.error.InvalidTypeArityException;
    import tonkadur.fate.v1.error.UpdatingIllegalVariableFromChoiceException;
    import tonkadur.fate.v1.error.UnknownExtensionContentException;
 
@@ -228,13 +232,33 @@ first_level_instruction
 
          if (arg_count < 0)
          {
-            // TODO: show error.
+            ErrorManager.handle
+            (
+               new BasicParsingError
+               (
+                  ErrorLevel.FATAL,
+                  ErrorCategory.INVALID_INPUT,
+                  start_origin.with_hint("second parameter"),
+                  "An integer higher than zero is needed here."
+               )
+            );
          }
       }
       catch (final Exception e)
       {
          arg_count = 0;
-         // TODO: show error.
+
+         ErrorManager.handle
+         (
+            new BasicParsingError
+            (
+               ErrorLevel.FATAL,
+               ErrorCategory.INVALID_INPUT,
+               start_origin.with_hint("second parameter"),
+               "An integer higher than zero is needed here."
+            )
+         );
+
          throw e;
       }
 
@@ -245,7 +269,18 @@ first_level_instruction
       catch (final Exception e)
       {
          is_comparable = false;
-         // TODO: show error.
+
+         ErrorManager.handle
+         (
+            new BasicParsingError
+            (
+               ErrorLevel.FATAL,
+               ErrorCategory.INVALID_INPUT,
+               start_origin.with_hint("third parameter"),
+               "An boolean is needed here."
+            )
+         );
+
          throw e;
       }
 
@@ -1649,7 +1684,10 @@ returns [Type result]
 
       if ($result.get_parameters().size() != 0)
       {
-         // TODO: throw error.
+         ErrorManager.handle
+         (
+            new InvalidTypeArityException(($word.origin), ($result))
+         );
       }
    }
 
diff --git a/src/core/src/tonkadur/parser/BasicParsingError.java b/src/core/src/tonkadur/parser/BasicParsingError.java
new file mode 100644
index 0000000..f003e77
--- /dev/null
+++ b/src/core/src/tonkadur/parser/BasicParsingError.java
@@ -0,0 +1,36 @@
+package tonkadur.parser;
+
+import tonkadur.error.ErrorCategory;
+import tonkadur.error.ErrorLevel;
+
+public class BasicParsingError extends ParsingError
+{
+   protected final String description;
+
+   public BasicParsingError
+   (
+      final ErrorLevel error_level,
+      final ErrorCategory error_category,
+      final Origin origin,
+      final String description
+   )
+   {
+      super(error_level, error_category, origin);
+
+      this.description = description;
+   }
+
+   @Override
+   public String toString ()
+   {
+      final StringBuilder sb = new StringBuilder();
+
+      sb.append(origin.toString());
+      sb.append(" ");
+      sb.append(error_category.toString());
+      sb.append(System.lineSeparator());
+      sb.append(description);
+
+      return sb.toString();
+   }
+}