Cleans up instruction building asserts.

29 files changed, 528 insertions, 1383 deletions

diff --git a/src/core/src/tonkadur/fate/v1/error/IncorrectReturnTypeException.java b/src/core/src/tonkadur/fate/v1/error/IncorrectReturnTypeException.java
new file mode 100644
index 0000000..5ea4457
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/IncorrectReturnTypeException.java
@@ -0,0 +1,60 @@
+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 IncorrectReturnTypeException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final Type given_type;
+   protected final Type allowed_type;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public IncorrectReturnTypeException
+   (
+      final Origin call_origin,
+      final Type given_type,
+      final Type allowed_type
+   )
+   {
+      super
+      (
+         ErrorLevel.FATAL,
+         ErrorCategory.INVALID_USE,
+         call_origin
+      );
+
+      this.given_type = given_type;
+      this.allowed_type = allowed_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("Return type '");
+      sb.append(given_type.toString());
+      sb.append("'");
+
+      sb.append(" is not allowed here. Use '");
+      sb.append(allowed_type.toString());
+      sb.append("' instead.");
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/error/SignatureTypeMismatchException.java b/src/core/src/tonkadur/fate/v1/error/SignatureTypeMismatchException.java
new file mode 100644
index 0000000..7bc47d1
--- /dev/null
+++ b/src/core/src/tonkadur/fate/v1/error/SignatureTypeMismatchException.java
@@ -0,0 +1,76 @@
+package tonkadur.fate.v1.error;
+
+import java.util.List;
+
+import tonkadur.error.ErrorLevel;
+
+import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
+
+import tonkadur.fate.v1.lang.type.Type;
+
+public class SignatureTypeMismatchException extends ParsingError
+{
+   /***************************************************************************/
+   /**** MEMBERS **************************************************************/
+   /***************************************************************************/
+   protected final List<Type> given_signature;
+   protected final List<Type> allowed_signature;
+
+   /***************************************************************************/
+   /**** PUBLIC ***************************************************************/
+   /***************************************************************************/
+   public SignatureTypeMismatchException
+   (
+      final Origin call_origin,
+      final List<Type> given_signature,
+      final List<Type> allowed_signature
+   )
+   {
+      super
+      (
+         ErrorLevel.FATAL,
+         ErrorCategory.INVALID_USE,
+         call_origin
+      );
+
+      this.given_signature = given_signature;
+      this.allowed_signature = allowed_signature;
+   }
+
+
+   @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("Given signature:");
+      sb.append(System.lineSeparator());
+
+      for (final Type t: given_signature)
+      {
+         sb.append("- ");
+         sb.append(t.toString());
+         sb.append(System.lineSeparator());
+      }
+
+      sb.append(System.lineSeparator());
+
+      sb.append("Expected signature:");
+      sb.append(System.lineSeparator());
+
+      for (final Type t: allowed_signature)
+      {
+         sb.append("- ");
+         sb.append(t.toString());
+         sb.append(System.lineSeparator());
+      }
+
+      return sb.toString();
+   }
+}
diff --git a/src/core/src/tonkadur/fate/v1/lang/computation/AddElementComputation.java b/src/core/src/tonkadur/fate/v1/lang/computation/AddElementComputation.java
index 82461d3..74e0fac 100644
--- a/src/core/src/tonkadur/fate/v1/lang/computation/AddElementComputation.java
+++ b/src/core/src/tonkadur/fate/v1/lang/computation/AddElementComputation.java
@@ -1,6 +1,7 @@
 package tonkadur.fate.v1.lang.computation;
 
 import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.error.ConflictingTypeException;
 import tonkadur.fate.v1.error.IncomparableTypeException;
@@ -42,10 +43,7 @@ public class AddElementComputation extends Computation
       final Computation element,
       final Computation collection
    )
-   throws
-      InvalidTypeException,
-      ConflictingTypeException,
-      IncomparableTypeException
+   throws ParsingError
    {
       return
          new AddElementComputation
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/DoWhile.java b/src/core/src/tonkadur/fate/v1/lang/instruction/DoWhile.java
index 1eaed2a..4fe170f 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/DoWhile.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/DoWhile.java
@@ -1,19 +1,16 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
 import java.util.List;
 
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.type.Type;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class DoWhile extends Instruction
 {
@@ -50,20 +47,9 @@ public class DoWhile extends Instruction
       final Computation condition,
       final List<Instruction> body
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
-      if (!condition.get_type().get_base_type().equals(Type.BOOL))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               condition.get_origin(),
-               condition.get_type(),
-               Collections.singleton(Type.BOOL)
-            )
-         );
-      }
+      RecurrentChecks.assert_can_be_used_as(condition, Type.BOOL);
 
       return new DoWhile(origin, condition, body);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/EventCall.java b/src/core/src/tonkadur/fate/v1/lang/instruction/EventCall.java
index 887e08b..16d23ed 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/EventCall.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/EventCall.java
@@ -1,19 +1,10 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.ArrayList;
 import java.util.List;
 
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
-import tonkadur.functional.Merge;
-
-import tonkadur.error.ErrorManager;
-
-import tonkadur.fate.v1.error.IncompatibleTypeException;
-import tonkadur.fate.v1.error.IncomparableTypeException;
-import tonkadur.fate.v1.error.InvalidArityException;
-
 import tonkadur.fate.v1.lang.Event;
 
 import tonkadur.fate.v1.lang.type.Type;
@@ -21,6 +12,7 @@ import tonkadur.fate.v1.lang.type.Type;
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class EventCall extends Instruction
 {
@@ -57,80 +49,14 @@ public class EventCall extends Instruction
       final Event event,
       final List<Computation> parameters
    )
-   throws Throwable
+   throws ParsingError
    {
-      final List<Boolean> type_checks;
-      final List<Type> signature;
-
-      signature = event.get_signature();
-
-      if (parameters.size() != signature.size())
-      {
-         ErrorManager.handle
-         (
-            new InvalidArityException
-            (
-               origin,
-               parameters.size(),
-               signature.size(),
-               signature.size()
-            )
-         );
-      }
-
-      (new Merge<Type, Computation, Boolean>()
-      {
-         @Override
-         public Boolean risky_lambda (final Type t, final Computation p)
-         throws ParsingError
-         {
-            if ((t == null) || (p == null))
-            {
-               return Boolean.FALSE;
-            }
-            else
-            {
-               final Type hint;
-
-               if (p.get_type().can_be_used_as(t))
-               {
-                  return Boolean.TRUE;
-               }
-
-               if (p.get_type().try_merging_with(t) != null)
-               {
-                  return Boolean.TRUE;
-               }
-
-               ErrorManager.handle
-               (
-                  new IncompatibleTypeException
-                  (
-                     p.get_origin(),
-                     p.get_type(),
-                     t
-                  )
-               );
-
-               hint = (Type) p.get_type().generate_comparable_to(t);
-
-               if (hint.equals(Type.ANY))
-               {
-                  ErrorManager.handle
-                  (
-                     new IncomparableTypeException
-                     (
-                        p.get_origin(),
-                        p.get_type(),
-                        t
-                     )
-                  );
-               }
-
-               return Boolean.FALSE;
-            }
-         }
-      }).risky_merge(signature, parameters);
+      RecurrentChecks.assert_computations_matches_signature
+      (
+         origin,
+         parameters,
+         event.get_signature()
+      );
 
       return new EventCall(origin, event, parameters);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/Filter.java b/src/core/src/tonkadur/fate/v1/lang/instruction/Filter.java
index d5f75b5..d81997c 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/Filter.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/Filter.java
@@ -1,19 +1,11 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
-import tonkadur.error.ErrorManager;
-
-import tonkadur.fate.v1.error.IncompatibleTypeException;
-import tonkadur.fate.v1.error.IncomparableTypeException;
-import tonkadur.fate.v1.error.InvalidArityException;
-import tonkadur.fate.v1.error.InvalidTypeException;
-
 import tonkadur.fate.v1.lang.type.Type;
 import tonkadur.fate.v1.lang.type.LambdaType;
 import tonkadur.fate.v1.lang.type.CollectionType;
@@ -22,6 +14,7 @@ import tonkadur.fate.v1.lang.meta.Computation;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Reference;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class Filter extends Instruction
 {
@@ -58,88 +51,21 @@ public class Filter extends Instruction
       final Computation lambda_function,
       final Reference collection
    )
-   throws Throwable
+   throws ParsingError
    {
-      final Type var_type, collection_generic_type;
-      final Type collection_out_generic_type;
-      final CollectionType collection_type;
-      final LambdaType lambda_type;
-      final List<Type> signature;
-
-      var_type = lambda_function.get_type();
-
-      if (!(var_type instanceof LambdaType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               origin,
-               var_type,
-               Collections.singleton(Type.LAMBDA)
-            )
-         );
-
-         return null;
-      }
-
-      lambda_type = (LambdaType) var_type;
 
-      signature = lambda_type.get_signature();
-
-      if (signature.size() != 1)
-      {
-         ErrorManager.handle
-         (
-            new InvalidArityException
-            (
-               lambda_function.get_origin(),
-               signature.size(),
-               1,
-               1
-            )
-         );
-      }
-
-      collection_generic_type = collection.get_type();
-
-      if (!(collection_generic_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection.get_origin(),
-               collection_generic_type,
-               Type.COLLECTION_TYPES
-            )
-         );
-
-         return null;
-      }
-
-      collection_type = (CollectionType) collection_generic_type;
-
-      if
+      RecurrentChecks.assert_is_a_collection(collection);
+      RecurrentChecks.assert_lambda_matches_types
       (
-         !collection_type.get_content_type().can_be_used_as(signature.get(0))
-      )
-      {
-         /* TODO */
-      }
-
-      if (lambda_type.get_return_type().can_be_used_as(Type.BOOL))
-      {
-         /* TODO */
-      }
-
-      return
-         new Filter
+         lambda_function,
+         Type.BOOL,
+         Collections.singletonList
          (
-            origin,
-            lambda_function,
-            collection
-         );
+            ((CollectionType) collection.get_type()).get_content_type()
+         )
+      );
+
+      return new Filter(origin, lambda_function, collection);
    }
 
    /**** Accessors ************************************************************/
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/For.java b/src/core/src/tonkadur/fate/v1/lang/instruction/For.java
index 45f50b9..b6734b2 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/For.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/For.java
@@ -1,19 +1,16 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
 import java.util.List;
 
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.type.Type;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class For extends Instruction
 {
@@ -58,20 +55,9 @@ public class For extends Instruction
       final List<Instruction> body,
       final Instruction post
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
-      if (!condition.get_type().get_base_type().equals(Type.BOOL))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               condition.get_origin(),
-               condition.get_type(),
-               Collections.singleton(Type.BOOL)
-            )
-         );
-      }
+      RecurrentChecks.assert_can_be_used_as(condition, Type.BOOL);
 
       return new For(origin, condition, pre, body, post);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/ForEach.java b/src/core/src/tonkadur/fate/v1/lang/instruction/ForEach.java
index e7937f7..cd1c4d0 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/ForEach.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/ForEach.java
@@ -14,6 +14,7 @@ import tonkadur.fate.v1.lang.type.Type;
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Reference;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class ForEach extends Instruction
 {
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/IfElseInstruction.java b/src/core/src/tonkadur/fate/v1/lang/instruction/IfElseInstruction.java
index 0a4f9d9..477b227 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/IfElseInstruction.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/IfElseInstruction.java
@@ -1,18 +1,14 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
-
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.type.Type;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class IfElseInstruction extends Instruction
 {
@@ -53,20 +49,9 @@ public class IfElseInstruction extends Instruction
       final Instruction if_true,
       final Instruction if_false
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
-      if (!condition.get_type().get_base_type().equals(Type.BOOL))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               condition.get_origin(),
-               condition.get_type(),
-               Collections.singleton(Type.BOOL)
-            )
-         );
-      }
+      RecurrentChecks.assert_can_be_used_as(condition, Type.BOOL);
 
       return new IfElseInstruction(origin, condition, if_true, if_false);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/IfInstruction.java b/src/core/src/tonkadur/fate/v1/lang/instruction/IfInstruction.java
index fab144a..a8751d1 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/IfInstruction.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/IfInstruction.java
@@ -1,18 +1,14 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
-
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.type.Type;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class IfInstruction extends Instruction
 {
@@ -49,20 +45,9 @@ public class IfInstruction extends Instruction
       final Computation condition,
       final Instruction if_true
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
-      if (!condition.get_type().get_base_type().equals(Type.BOOL))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               condition.get_origin(),
-               condition.get_type(),
-               Collections.singleton(Type.BOOL)
-            )
-         );
-      }
+      RecurrentChecks.assert_can_be_used_as(condition, Type.BOOL);
 
       return new IfInstruction(origin, condition, if_true);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/IndexedMap.java b/src/core/src/tonkadur/fate/v1/lang/instruction/IndexedMap.java
index d031559..5040987 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/IndexedMap.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/IndexedMap.java
@@ -1,27 +1,19 @@
 package tonkadur.fate.v1.lang.instruction;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
-import tonkadur.error.ErrorManager;
-
-import tonkadur.fate.v1.error.IncompatibleTypeException;
-import tonkadur.fate.v1.error.IncomparableTypeException;
-import tonkadur.fate.v1.error.InvalidArityException;
-import tonkadur.fate.v1.error.InvalidTypeException;
-
 import tonkadur.fate.v1.lang.type.Type;
-import tonkadur.fate.v1.lang.type.LambdaType;
 import tonkadur.fate.v1.lang.type.CollectionType;
 
 import tonkadur.fate.v1.lang.meta.Computation;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Reference;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class IndexedMap extends Instruction
 {
@@ -64,121 +56,28 @@ public class IndexedMap extends Instruction
    )
    throws Throwable
    {
-      final Type var_type, collection_in_generic_type;
-      final Type collection_out_generic_type;
-      final CollectionType collection_in_type;
-      final CollectionType collection_out_type;
-      final LambdaType lambda_type;
-      final List<Type> signature;
-
-      var_type = lambda_function.get_type();
-
-      if (!(var_type instanceof LambdaType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               origin,
-               var_type,
-               Collections.singleton(Type.LAMBDA)
-            )
-         );
-
-         return null;
-      }
-
-      lambda_type = (LambdaType) var_type;
-
-      signature = lambda_type.get_signature();
-
-      if (signature.size() != 1)
-      {
-         ErrorManager.handle
-         (
-            new InvalidArityException
-            (
-               lambda_function.get_origin(),
-               signature.size(),
-               1,
-               1
-            )
-         );
-      }
-
-      collection_in_generic_type = collection_in.get_type();
-
-      if (!(collection_in_generic_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection_in.get_origin(),
-               collection_in_generic_type,
-               Type.COLLECTION_TYPES
-            )
-         );
-
-         return null;
-      }
-
-      collection_in_type = (CollectionType) collection_in_generic_type;
-
-      if
-      (
-         Type.INT.can_be_used_as(signature.get(0))
-      )
-      {
-         /* TODO */
-      }
+      final List<Type> in_types;
 
-      if
+      in_types = new ArrayList<Type>();
+
+      RecurrentChecks.assert_is_a_collection(collection_in);
+      RecurrentChecks.assert_is_a_collection(collection_out);
+
+      in_types.add(Type.INT);
+      in_types.add
       (
-         !collection_in_type.get_content_type().can_be_used_as(signature.get(1))
-      )
-      {
-         /* TODO */
-      }
-
-      collection_out_generic_type = collection_out.get_type();
-
-      if (!(collection_out_generic_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection_out.get_origin(),
-               collection_out_generic_type,
-               Type.COLLECTION_TYPES
-            )
-         );
-
-         return null;
-      }
-
-      collection_out_type = (CollectionType) collection_out_generic_type;
-
-      if
+         ((CollectionType) collection_in.get_type()).get_content_type()
+      );
+
+      RecurrentChecks.assert_lambda_matches_types
       (
-         !collection_out_type.get_content_type().can_be_used_as
-         (
-            lambda_type.get_return_type()
-         )
-      )
-      {
-         /* TODO */
-      }
+         lambda_function,
+         ((CollectionType) collection_out.get_type()).get_content_type(),
+         in_types
+      );
 
       return
-         new IndexedMap
-         (
-            origin,
-            lambda_function,
-            collection_in,
-            collection_out
-         );
+         new IndexedMap(origin, lambda_function, collection_in, collection_out);
    }
 
    /**** Accessors ************************************************************/
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/Map.java b/src/core/src/tonkadur/fate/v1/lang/instruction/Map.java
index 2123ee4..46a728c 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/Map.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/Map.java
@@ -1,25 +1,19 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
-import tonkadur.error.ErrorManager;
-
-import tonkadur.fate.v1.error.InvalidArityException;
-import tonkadur.fate.v1.error.InvalidTypeException;
-
 import tonkadur.fate.v1.lang.type.Type;
-import tonkadur.fate.v1.lang.type.LambdaType;
 import tonkadur.fate.v1.lang.type.CollectionType;
 
 import tonkadur.fate.v1.lang.meta.Computation;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Reference;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class Map extends Instruction
 {
@@ -60,115 +54,21 @@ public class Map extends Instruction
       final Reference collection_in,
       final Reference collection_out
    )
-   throws Throwable
+   throws ParsingError
    {
-      final Type var_type, collection_in_generic_type;
-      final Type collection_out_generic_type;
-      final CollectionType collection_in_type;
-      final CollectionType collection_out_type;
-      final LambdaType lambda_type;
-      final List<Type> signature;
-
-      var_type = lambda_function.get_type();
-
-      if (!(var_type instanceof LambdaType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               origin,
-               var_type,
-               Collections.singleton(Type.LAMBDA)
-            )
-         );
-
-         return null;
-      }
-
-      lambda_type = (LambdaType) var_type;
-
-      signature = lambda_type.get_signature();
-
-      if (signature.size() != 1)
-      {
-         ErrorManager.handle
-         (
-            new InvalidArityException
-            (
-               lambda_function.get_origin(),
-               signature.size(),
-               1,
-               1
-            )
-         );
-      }
-
-      collection_in_generic_type = collection_in.get_type();
-
-      if (!(collection_in_generic_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection_in.get_origin(),
-               collection_in_generic_type,
-               Type.COLLECTION_TYPES
-            )
-         );
-
-         return null;
-      }
-
-      collection_in_type = (CollectionType) collection_in_generic_type;
-
-      if
-      (
-         !collection_in_type.get_content_type().can_be_used_as(signature.get(0))
-      )
-      {
-         /* TODO */
-      }
-
-      collection_out_generic_type = collection_out.get_type();
-
-      if (!(collection_out_generic_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection_out.get_origin(),
-               collection_out_generic_type,
-               Type.COLLECTION_TYPES
-            )
-         );
-
-         return null;
-      }
-
-      collection_out_type = (CollectionType) collection_out_generic_type;
-
-      if
+      RecurrentChecks.assert_is_a_collection(collection_in);
+      RecurrentChecks.assert_is_a_collection(collection_out);
+      RecurrentChecks.assert_lambda_matches_types
       (
-         !collection_out_type.get_content_type().can_be_used_as
+         lambda_function,
+         ((CollectionType) collection_out.get_type()).get_content_type(),
+         Collections.singletonList
          (
-            lambda_type.get_return_type()
+            ((CollectionType) collection_in.get_type()).get_content_type()
          )
-      )
-      {
-         /* TODO */
-      }
+      );
 
-      return
-         new Map
-         (
-            origin,
-            lambda_function,
-            collection_in,
-            collection_out
-         );
+      return new Map(origin, lambda_function, collection_in, collection_out);
    }
 
    /**** Accessors ************************************************************/
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/Merge.java b/src/core/src/tonkadur/fate/v1/lang/instruction/Merge.java
index f2fe200..1dd9b91 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/Merge.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/Merge.java
@@ -1,27 +1,19 @@
 package tonkadur.fate.v1.lang.instruction;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
-import tonkadur.error.ErrorManager;
-
-import tonkadur.fate.v1.error.IncompatibleTypeException;
-import tonkadur.fate.v1.error.IncomparableTypeException;
-import tonkadur.fate.v1.error.InvalidArityException;
-import tonkadur.fate.v1.error.InvalidTypeException;
-
 import tonkadur.fate.v1.lang.type.Type;
-import tonkadur.fate.v1.lang.type.LambdaType;
 import tonkadur.fate.v1.lang.type.CollectionType;
 
 import tonkadur.fate.v1.lang.meta.Computation;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Reference;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class Merge extends Instruction
 {
@@ -76,170 +68,46 @@ public class Merge extends Instruction
    )
    throws Throwable
    {
-      final Type var_type, collection_in_a_generic_type;
-      final Type collection_in_b_generic_type, collection_out_generic_type;
-      final CollectionType collection_in_a_type, collection_in_b_type;
-      final CollectionType collection_out_type;
-      final LambdaType lambda_type;
-      final List<Type> signature;
+      final List<Type> types_in;
 
-      var_type = lambda_function.get_type();
+      types_in = new ArrayList<Type>();
 
-      if (!(var_type instanceof LambdaType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               origin,
-               var_type,
-               Collections.singleton(Type.LAMBDA)
-            )
-         );
+      RecurrentChecks.assert_is_a_collection(collection_out);
 
-         return null;
-      }
-
-      lambda_type = (LambdaType) var_type;
-
-      signature = lambda_type.get_signature();
-
-      if (signature.size() != 2)
+      if (default_a == null)
       {
-         ErrorManager.handle
-         (
-            new InvalidArityException
-            (
-               lambda_function.get_origin(),
-               signature.size(),
-               2,
-               2
-            )
-         );
+         RecurrentChecks.assert_is_a_collection(collection_in_a);
       }
-
-      collection_in_a_generic_type = collection_in_a.get_type();
-
-      if (!(collection_in_a_generic_type instanceof CollectionType))
+      else
       {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection_in_a.get_origin(),
-               collection_in_a_generic_type,
-               Type.COLLECTION_TYPES
-            )
-         );
-
-         return null;
+         RecurrentChecks.assert_is_a_collection_of(collection_in_a, default_a);
       }
 
-      collection_in_a_type = (CollectionType) collection_in_a_generic_type;
-
-      if
-      (
-         !collection_in_a_type.get_content_type().can_be_used_as
-         (
-            signature.get(0)
-         )
-      )
+      if (default_b == null)
       {
-         /* TODO */
+         RecurrentChecks.assert_is_a_collection(collection_in_b);
       }
-
-      collection_in_b_generic_type = collection_in_b.get_type();
-
-      if (!(collection_in_b_generic_type instanceof CollectionType))
+      else
       {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection_in_b.get_origin(),
-               collection_in_b_generic_type,
-               Type.COLLECTION_TYPES
-            )
-         );
-
-         return null;
+         RecurrentChecks.assert_is_a_collection_of(collection_in_b, default_b);
       }
 
-      collection_in_b_type = (CollectionType) collection_in_b_generic_type;
-
-      if
+      types_in.add
       (
-         !collection_in_b_type.get_content_type().can_be_used_as
-         (
-            signature.get(1)
-         )
-      )
-      {
-         /* TODO */
-      }
+         ((CollectionType) collection_in_a.get_type()).get_content_type()
+      );
 
-      if
+      types_in.add
       (
-         (default_a != null)
-         &&
-         (
-            collection_in_a_type.get_content_type().can_be_used_as
-            (
-               default_a.get_type()
-            )
-         )
-      )
-      {
-         /* TODO */
-      }
+         ((CollectionType) collection_in_b.get_type()).get_content_type()
+      );
 
-      if
+      RecurrentChecks.assert_lambda_matches_types
       (
-         (default_b != null)
-         &&
-         (
-            collection_in_b_type.get_content_type().can_be_used_as
-            (
-               default_b.get_type()
-            )
-         )
-      )
-      {
-         /* TODO */
-      }
-
-      if (collection_out != null)
-      {
-         collection_out_generic_type = collection_out.get_type();
-
-         if (!(collection_out_generic_type instanceof CollectionType))
-         {
-            ErrorManager.handle
-            (
-               new InvalidTypeException
-               (
-                  collection_out.get_origin(),
-                  collection_out_generic_type,
-                  Type.COLLECTION_TYPES
-               )
-            );
-
-            return null;
-         }
-
-         collection_out_type = (CollectionType) collection_out_generic_type;
-
-         if
-         (
-            !collection_out_type.get_content_type().can_be_used_as
-            (
-               lambda_type.get_return_type()
-            )
-         )
-         {
-            /* TODO */
-         }
-      }
+         lambda_function,
+         ((CollectionType) collection_out.get_type()).get_content_type(),
+         types_in
+      );
 
       return
          new Merge
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/Partition.java b/src/core/src/tonkadur/fate/v1/lang/instruction/Partition.java
index 220f345..c075c9b 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/Partition.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/Partition.java
@@ -1,27 +1,18 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.ArrayList;
 import java.util.Collections;
-import java.util.List;
 
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
-import tonkadur.error.ErrorManager;
-
-import tonkadur.fate.v1.error.IncompatibleTypeException;
-import tonkadur.fate.v1.error.IncomparableTypeException;
-import tonkadur.fate.v1.error.InvalidArityException;
-import tonkadur.fate.v1.error.InvalidTypeException;
-
 import tonkadur.fate.v1.lang.type.Type;
-import tonkadur.fate.v1.lang.type.LambdaType;
 import tonkadur.fate.v1.lang.type.CollectionType;
 
 import tonkadur.fate.v1.lang.meta.Computation;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Reference;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class Partition extends Instruction
 {
@@ -62,84 +53,25 @@ public class Partition extends Instruction
       final Reference collection_in,
       final Reference collection_out
    )
-   throws Throwable
+   throws ParsingError
    {
-      final Type var_type, collection_in_generic_type;
-      final CollectionType collection_in_type;
-      final LambdaType lambda_type;
-      final List<Type> signature;
-
-      var_type = lambda_function.get_type();
-
-      if (!(var_type instanceof LambdaType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               origin,
-               var_type,
-               Collections.singleton(Type.LAMBDA)
-            )
-         );
-
-         return null;
-      }
-
-      lambda_type = (LambdaType) var_type;
-
-      signature = lambda_type.get_signature();
-
-      if (signature.size() != 1)
-      {
-         ErrorManager.handle
-         (
-            new InvalidArityException
-            (
-               lambda_function.get_origin(),
-               signature.size(),
-               1,
-               1
-            )
-         );
-      }
-
-      collection_in_generic_type = collection_in.get_type();
-
-      if (!(collection_in_generic_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection_in.get_origin(),
-               collection_in_generic_type,
-               Type.COLLECTION_TYPES
-            )
-         );
-
-         return null;
-      }
-
-      collection_in_type = (CollectionType) collection_in_generic_type;
+      RecurrentChecks.assert_is_a_collection(collection_in);
+      RecurrentChecks.assert_is_a_collection(collection_out);
+      RecurrentChecks.assert_can_be_used_as
+      (
+         collection_in,
+         collection_out.get_type()
+      );
 
-      if
+      RecurrentChecks.assert_lambda_matches_types
       (
-         !collection_in_type.get_content_type().can_be_used_as(signature.get(0))
-      )
-      {
-         /* TODO */
-      }
-
-      if (lambda_type.get_return_type().can_be_used_as(Type.BOOL))
-      {
-         /* TODO */
-      }
-
-      if (!collection_in_type.can_be_used_as(collection_out.get_type()))
-      {
-         /* TODO */
-      }
+         lambda_function,
+         Type.BOOL,
+         Collections.singletonList
+         (
+            ((CollectionType) collection_in.get_type()).get_content_type()
+         )
+      );
 
       return
          new Partition
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/PopElement.java b/src/core/src/tonkadur/fate/v1/lang/instruction/PopElement.java
index 7729164..9ea468f 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/PopElement.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/PopElement.java
@@ -1,17 +1,12 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
-
-import tonkadur.fate.v1.lang.type.CollectionType;
-import tonkadur.fate.v1.lang.type.Type;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class PopElement extends Instruction
 {
@@ -48,26 +43,9 @@ public class PopElement extends Instruction
       final Computation collection,
       final boolean is_from_left
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
-      if
-      (
-         !Type.COLLECTION_TYPES.contains
-         (
-            collection.get_type().get_act_as_type()
-         )
-      )
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection.get_origin(),
-               collection.get_type(),
-               Type.COLLECTION_TYPES
-            )
-         );
-      }
+      RecurrentChecks.assert_is_a_collection(collection);
 
       return new PopElement(origin, collection, is_from_left);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/PromptInteger.java b/src/core/src/tonkadur/fate/v1/lang/instruction/PromptInteger.java
index ae28617..8c76365 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/PromptInteger.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/PromptInteger.java
@@ -1,18 +1,15 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
-
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.type.Type;
+import tonkadur.fate.v1.lang.type.PointerType;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class PromptInteger extends Instruction
 {
@@ -57,46 +54,16 @@ public class PromptInteger extends Instruction
       final Computation max,
       final Computation label
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
-      if (!target.get_type().can_be_used_as(Type.INT))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               target.get_origin(),
-               target.get_type(),
-               Collections.singletonList(Type.INT)
-            )
-         );
-      }
-
-      if (!min.get_type().can_be_used_as(Type.INT))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               min.get_origin(),
-               min.get_type(),
-               Collections.singletonList(Type.INT)
-            )
-         );
-      }
-
-      if (!max.get_type().can_be_used_as(Type.INT))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               min.get_origin(),
-               min.get_type(),
-               Collections.singletonList(Type.INT)
-            )
-         );
-      }
+      RecurrentChecks.assert_can_be_used_as(min, Type.INT);
+      RecurrentChecks.assert_can_be_used_as(max, Type.INT);
+      RecurrentChecks.assert_can_be_used_as(label, Type.RICH_TEXT);
+      RecurrentChecks.assert_can_be_used_as
+      (
+         target,
+         new PointerType(origin, Type.INT, "auto generated")
+      );
 
       return new PromptInteger(origin, target, min, max, label);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/PromptString.java b/src/core/src/tonkadur/fate/v1/lang/instruction/PromptString.java
index e857952..a0a8a42 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/PromptString.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/PromptString.java
@@ -1,18 +1,15 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
-
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.type.Type;
+import tonkadur.fate.v1.lang.type.PointerType;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class PromptString extends Instruction
 {
@@ -57,46 +54,16 @@ public class PromptString extends Instruction
       final Computation max,
       final Computation label
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
-      if (!target.get_type().can_be_used_as(Type.STRING))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               target.get_origin(),
-               target.get_type(),
-               Collections.singletonList(Type.STRING)
-            )
-         );
-      }
-
-      if (!min.get_type().can_be_used_as(Type.INT))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               min.get_origin(),
-               min.get_type(),
-               Collections.singletonList(Type.INT)
-            )
-         );
-      }
-
-      if (!max.get_type().can_be_used_as(Type.INT))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               min.get_origin(),
-               min.get_type(),
-               Collections.singletonList(Type.INT)
-            )
-         );
-      }
+      RecurrentChecks.assert_can_be_used_as(min, Type.INT);
+      RecurrentChecks.assert_can_be_used_as(max, Type.INT);
+      RecurrentChecks.assert_can_be_used_as(label, Type.RICH_TEXT);
+      RecurrentChecks.assert_can_be_used_as
+      (
+         target,
+         new PointerType(origin, Type.STRING, "auto generated")
+      );
 
       return new PromptString(origin, target, min, max, label);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/PushElement.java b/src/core/src/tonkadur/fate/v1/lang/instruction/PushElement.java
index 8f0474a..0ab34d4 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/PushElement.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/PushElement.java
@@ -1,21 +1,12 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
-
-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.InvalidTypeException;
-
-import tonkadur.fate.v1.lang.type.CollectionType;
-import tonkadur.fate.v1.lang.type.Type;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class PushElement extends Instruction
 {
@@ -56,86 +47,9 @@ public class PushElement extends Instruction
       final Computation collection,
       final boolean is_from_left
    )
-   throws
-      InvalidTypeException,
-      ConflictingTypeException,
-      IncomparableTypeException
+   throws ParsingError
    {
-      final Type hint;
-      final Type collection_type;
-      final CollectionType collection_true_type;
-      final Type collection_element_type;
-
-      collection_type = collection.get_type();
-
-      if (!(collection_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection.get_origin(),
-               collection.get_type(),
-               Collections.singletonList(Type.LIST)
-            )
-         );
-      }
-
-      collection_true_type = (CollectionType) collection_type;
-
-      if (collection_true_type.is_set())
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection.get_origin(),
-               collection.get_type(),
-               Collections.singletonList(Type.LIST)
-            )
-         );
-      }
-
-      collection_element_type = collection_true_type.get_content_type();
-
-      if
-      (
-         element.get_type().can_be_used_as(collection_element_type)
-         ||
-         (element.get_type().try_merging_with(collection_element_type) != null)
-      )
-      {
-         return new PushElement(origin, element, collection, is_from_left);
-      }
-
-      ErrorManager.handle
-      (
-         new ConflictingTypeException
-         (
-            element.get_origin(),
-            element.get_type(),
-            collection_element_type
-         )
-      );
-
-      hint =
-         (Type) element.get_type().generate_comparable_to
-         (
-            collection_element_type
-         );
-
-      if (hint.equals(Type.ANY))
-      {
-         ErrorManager.handle
-         (
-            new IncomparableTypeException
-            (
-               element.get_origin(),
-               element.get_type(),
-               collection_element_type
-            )
-         );
-      }
+      RecurrentChecks.assert_is_a_list_of(collection, element);
 
       return new PushElement(origin, element, collection, is_from_left);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveAllOfElement.java b/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveAllOfElement.java
index acce7d0..b8ef9de 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveAllOfElement.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveAllOfElement.java
@@ -1,20 +1,13 @@
 package tonkadur.fate.v1.lang.instruction;
 
-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.InvalidTypeException;
-
-import tonkadur.fate.v1.lang.type.CollectionType;
-import tonkadur.fate.v1.lang.type.Type;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
 import tonkadur.fate.v1.lang.meta.Reference;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class RemoveAllOfElement extends Instruction
 {
@@ -51,72 +44,9 @@ public class RemoveAllOfElement extends Instruction
       final Computation element,
       final Reference collection
    )
-   throws
-      InvalidTypeException,
-      ConflictingTypeException,
-      IncomparableTypeException
+   throws ParsingError
    {
-      final Type hint;
-      final Type collection_type;
-      final CollectionType collection_true_type;
-      final Type collection_element_type;
-
-      collection_type = collection.get_type();
-
-      if (!(collection_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection.get_origin(),
-               collection.get_type(),
-               Type.COLLECTION_TYPES
-            )
-         );
-      }
-
-      collection_true_type = (CollectionType) collection_type;
-      collection_element_type = collection_true_type.get_content_type();
-
-      if
-      (
-         element.get_type().can_be_used_as(collection_element_type)
-         ||
-         (element.get_type().try_merging_with(collection_element_type) != null)
-      )
-      {
-         return new RemoveAllOfElement(origin, element, collection);
-      }
-
-      ErrorManager.handle
-      (
-         new ConflictingTypeException
-         (
-            element.get_origin(),
-            element.get_type(),
-            collection_element_type
-         )
-      );
-
-      hint =
-         (Type) element.get_type().generate_comparable_to
-         (
-            collection_element_type
-         );
-
-      if (hint.equals(Type.ANY))
-      {
-         ErrorManager.handle
-         (
-            new IncomparableTypeException
-            (
-               element.get_origin(),
-               element.get_type(),
-               collection_element_type
-            )
-         );
-      }
+      RecurrentChecks.assert_is_a_collection_of(collection, element);
 
       return new RemoveAllOfElement(origin, element, collection);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveElement.java b/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveElement.java
index d721614..ac4d093 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveElement.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveElement.java
@@ -1,19 +1,12 @@
 package tonkadur.fate.v1.lang.instruction;
 
-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.InvalidTypeException;
-
-import tonkadur.fate.v1.lang.type.CollectionType;
-import tonkadur.fate.v1.lang.type.Type;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class RemoveElement extends Instruction
 {
@@ -50,72 +43,9 @@ public class RemoveElement extends Instruction
       final Computation element,
       final Computation collection
    )
-   throws
-      InvalidTypeException,
-      ConflictingTypeException,
-      IncomparableTypeException
+   throws ParsingError
    {
-      final Type hint;
-      final Type collection_type;
-      final CollectionType collection_true_type;
-      final Type collection_element_type;
-
-      collection_type = collection.get_type();
-
-      if (!(collection_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection.get_origin(),
-               collection.get_type(),
-               Type.COLLECTION_TYPES
-            )
-         );
-      }
-
-      collection_true_type = (CollectionType) collection_type;
-      collection_element_type = collection_true_type.get_content_type();
-
-      if
-      (
-         element.get_type().can_be_used_as(collection_element_type)
-         ||
-         (element.get_type().try_merging_with(collection_element_type) != null)
-      )
-      {
-         return new RemoveElement(origin, element, collection);
-      }
-
-      ErrorManager.handle
-      (
-         new ConflictingTypeException
-         (
-            element.get_origin(),
-            element.get_type(),
-            collection_element_type
-         )
-      );
-
-      hint =
-         (Type) element.get_type().generate_comparable_to
-         (
-            collection_element_type
-         );
-
-      if (hint.equals(Type.ANY))
-      {
-         ErrorManager.handle
-         (
-            new IncomparableTypeException
-            (
-               element.get_origin(),
-               element.get_type(),
-               collection_element_type
-            )
-         );
-      }
+      RecurrentChecks.assert_is_a_collection_of(collection, element);
 
       return new RemoveElement(origin, element, collection);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveElementAt.java b/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveElementAt.java
index 3bf0104..750dafe 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveElementAt.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/RemoveElementAt.java
@@ -1,19 +1,15 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
 
-import tonkadur.fate.v1.error.IncomparableTypeException;
-import tonkadur.fate.v1.error.InvalidTypeException;
-
-import tonkadur.fate.v1.lang.type.CollectionType;
 import tonkadur.fate.v1.lang.type.Type;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
 import tonkadur.fate.v1.lang.meta.Reference;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class RemoveElementAt extends Instruction
 {
@@ -50,47 +46,10 @@ public class RemoveElementAt extends Instruction
       final Computation index,
       final Reference collection
    )
-   throws
-      InvalidTypeException,
-      IncomparableTypeException
+   throws ParsingError
    {
-      final Type collection_type, hint;
-
-      collection_type = collection.get_type();
-
-      if (!(collection_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection.get_origin(),
-               collection.get_type(),
-               Type.COLLECTION_TYPES
-            )
-         );
-      }
-
-      if (index.get_type().can_be_used_as(Type.INT))
-      {
-         return new RemoveElementAt(origin, index, collection);
-      }
-
-      hint =
-         (Type) index.get_type().generate_comparable_to(Type.INT);
-
-      if (hint.equals(Type.ANY))
-      {
-         ErrorManager.handle
-         (
-            new IncomparableTypeException
-            (
-               index.get_origin(),
-               index.get_type(),
-               Type.INT
-            )
-         );
-      }
+      RecurrentChecks.assert_is_a_collection(collection);
+      RecurrentChecks.assert_can_be_used_as(index, Type.INT);
 
       return new RemoveElementAt(origin, index, collection);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/ReverseList.java b/src/core/src/tonkadur/fate/v1/lang/instruction/ReverseList.java
index 59a68e6..9d84ee4 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/ReverseList.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/ReverseList.java
@@ -1,19 +1,12 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
-
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
-
-import tonkadur.fate.v1.lang.type.CollectionType;
-import tonkadur.fate.v1.lang.type.Type;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class ReverseList extends Instruction
 {
@@ -46,28 +39,9 @@ public class ReverseList extends Instruction
       final Origin origin,
       final Computation collection
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
-      final Type t;
-
-      t = collection.get_type();
-
-      if
-      (
-         !(t instanceof CollectionType)
-         || ((CollectionType) t).is_set()
-      )
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection.get_origin(),
-               collection.get_type(),
-               Collections.singleton(Type.LIST)
-            )
-         );
-      }
+      RecurrentChecks.assert_is_a_list(collection);
 
       return new ReverseList(origin, collection);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/SetValue.java b/src/core/src/tonkadur/fate/v1/lang/instruction/SetValue.java
index 6a7db6f..5983c03 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/SetValue.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/SetValue.java
@@ -1,18 +1,13 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
+import tonkadur.parser.ParsingError;
 
-import tonkadur.fate.v1.error.ConflictingTypeException;
-import tonkadur.fate.v1.error.IncomparableTypeException;
-import tonkadur.fate.v1.error.InvalidTypeException;
-
-import tonkadur.fate.v1.lang.type.Type;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class SetValue extends Instruction
 {
@@ -49,55 +44,9 @@ public class SetValue extends Instruction
       final Computation element,
       final Computation value_reference
    )
-   throws
-      InvalidTypeException,
-      ConflictingTypeException,
-      IncomparableTypeException
+   throws ParsingError
    {
-      final Type hint;
-      final Type value_reference_type;
-
-      value_reference_type = value_reference.get_type();
-
-      if
-      (
-         element.get_type().can_be_used_as(value_reference_type)
-         ||
-         (element.get_type().try_merging_with(value_reference_type) != null)
-      )
-      {
-         return new SetValue(origin, element, value_reference);
-      }
-
-
-      ErrorManager.handle
-      (
-         new ConflictingTypeException
-         (
-            element.get_origin(),
-            element.get_type(),
-            value_reference_type
-         )
-      );
-
-      hint =
-         (Type) element.get_type().generate_comparable_to
-         (
-            value_reference_type
-         );
-
-      if (hint.equals(Type.ANY))
-      {
-         ErrorManager.handle
-         (
-            new IncomparableTypeException
-            (
-               element.get_origin(),
-               element.get_type(),
-               value_reference_type
-            )
-         );
-      }
+      RecurrentChecks.assert_can_be_used_as(element, value_reference);
 
       return new SetValue(origin, element, value_reference);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/Shuffle.java b/src/core/src/tonkadur/fate/v1/lang/instruction/Shuffle.java
index ebac30e..82e746d 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/Shuffle.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/Shuffle.java
@@ -1,19 +1,14 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
-
 import tonkadur.error.ErrorManager;
 
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
-
-import tonkadur.fate.v1.lang.type.CollectionType;
-import tonkadur.fate.v1.lang.type.Type;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class Shuffle extends Instruction
 {
@@ -46,28 +41,9 @@ public class Shuffle extends Instruction
       final Origin origin,
       final Computation collection
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
-      final Type t;
-
-      t = collection.get_type();
-
-      if
-      (
-         !(t instanceof CollectionType)
-         || ((CollectionType) t).is_set()
-      )
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection.get_origin(),
-               collection.get_type(),
-               Collections.singleton(Type.LIST)
-            )
-         );
-      }
+      RecurrentChecks.assert_is_a_list(collection);
 
       return new Shuffle(origin, collection);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/Sort.java b/src/core/src/tonkadur/fate/v1/lang/instruction/Sort.java
index d9f3397..083b1a1 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/Sort.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/Sort.java
@@ -1,27 +1,19 @@
 package tonkadur.fate.v1.lang.instruction;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
-import tonkadur.error.ErrorManager;
-
-import tonkadur.fate.v1.error.IncompatibleTypeException;
-import tonkadur.fate.v1.error.IncomparableTypeException;
-import tonkadur.fate.v1.error.InvalidArityException;
-import tonkadur.fate.v1.error.InvalidTypeException;
-
 import tonkadur.fate.v1.lang.type.Type;
-import tonkadur.fate.v1.lang.type.LambdaType;
 import tonkadur.fate.v1.lang.type.CollectionType;
 
 import tonkadur.fate.v1.lang.meta.Computation;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Reference;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class Sort extends Instruction
 {
@@ -60,79 +52,21 @@ public class Sort extends Instruction
    )
    throws Throwable
    {
-      final Type var_type, collection_generic_type;
-      final CollectionType collection_type;
-      final LambdaType lambda_type;
-      final List<Type> signature;
-
-      var_type = lambda_function.get_type();
-
-      if (!(var_type instanceof LambdaType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               origin,
-               var_type,
-               Collections.singleton(Type.LAMBDA)
-            )
-         );
-
-         return null;
-      }
-
-      lambda_type = (LambdaType) var_type;
-
-      signature = lambda_type.get_signature();
-
-      if (signature.size() != 2)
-      {
-         ErrorManager.handle
-         (
-            new InvalidArityException
-            (
-               lambda_function.get_origin(),
-               signature.size(),
-               1,
-               1
-            )
-         );
-      }
-
-      collection_generic_type = collection.get_type();
-
-      if (!(collection_generic_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection.get_origin(),
-               collection_generic_type,
-               Type.COLLECTION_TYPES
-            )
-         );
-
-         return null;
-      }
-
-      collection_type = (CollectionType) collection_generic_type;
-
-      if (!collection_type.get_content_type().can_be_used_as(signature.get(0)))
-      {
-         /* TODO */
-      }
-
-      if (!collection_type.get_content_type().can_be_used_as(signature.get(1)))
-      {
-         /* TODO */
-      }
-
-      if (!lambda_type.get_return_type().can_be_used_as(Type.INT))
-      {
-         /* TODO */
-      }
+      final List<Type> types_in;
+
+      types_in = new ArrayList<Type>();
+
+      RecurrentChecks.assert_is_a_list(collection);
+
+      types_in.add(((CollectionType) collection.get_type()).get_content_type());
+      types_in.add(types_in.get(0));
+
+      RecurrentChecks.assert_lambda_matches_types
+      (
+         lambda_function,
+         Type.INT,
+         types_in
+      );
 
       return new Sort(origin, lambda_function, collection);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/SubList.java b/src/core/src/tonkadur/fate/v1/lang/instruction/SubList.java
index 607f7c1..918d6e0 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/SubList.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/SubList.java
@@ -1,26 +1,15 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
-
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
-import tonkadur.error.ErrorManager;
-
-import tonkadur.fate.v1.error.IncompatibleTypeException;
-import tonkadur.fate.v1.error.IncomparableTypeException;
-import tonkadur.fate.v1.error.InvalidArityException;
-import tonkadur.fate.v1.error.InvalidTypeException;
-
 import tonkadur.fate.v1.lang.type.Type;
-import tonkadur.fate.v1.lang.type.CollectionType;
 
 import tonkadur.fate.v1.lang.meta.Computation;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Reference;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class SubList extends Instruction
 {
@@ -67,29 +56,15 @@ public class SubList extends Instruction
    )
    throws Throwable
    {
-      final Type collection_generic_type;
-
-      collection_generic_type = collection_in.get_type();
-
-      if (!(collection_generic_type instanceof CollectionType))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               collection_in.get_origin(),
-               collection_generic_type,
-               Type.COLLECTION_TYPES
-            )
-         );
-
-         return null;
-      }
-
-      if (!collection_generic_type.can_be_used_as(collection_out.get_type()))
-      {
-         /* TODO */
-      }
+      RecurrentChecks.assert_is_a_collection(collection_in);
+      RecurrentChecks.assert_is_a_collection(collection_out);
+      RecurrentChecks.assert_can_be_used_as
+      (
+         collection_in,
+         collection_out.get_type()
+      );
+      RecurrentChecks.assert_can_be_used_as(start, Type.INT);
+      RecurrentChecks.assert_can_be_used_as(end, Type.INT);
 
       return new SubList(origin, start, end, collection_in, collection_out);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/SwitchInstruction.java b/src/core/src/tonkadur/fate/v1/lang/instruction/SwitchInstruction.java
index b67dc42..6c0b021 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/SwitchInstruction.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/SwitchInstruction.java
@@ -1,21 +1,18 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
 import java.util.List;
 
-import tonkadur.error.ErrorManager;
-
 import tonkadur.functional.Cons;
 
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.type.Type;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class SwitchInstruction extends Instruction
 {
@@ -56,7 +53,7 @@ public class SwitchInstruction extends Instruction
       final List<Cons<Computation, Instruction>> branches,
       final Instruction default_instruction
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
       final Type target_type;
 
@@ -64,21 +61,11 @@ public class SwitchInstruction extends Instruction
 
       for (final Cons<Computation, Instruction> branch: branches)
       {
-         if (!branch.get_car().get_type().get_base_type().equals(target_type))
-         {
-            ErrorManager.handle
-            (
-               new InvalidTypeException
-               (
-                  branch.get_car().get_origin(),
-                  branch.get_car().get_type(),
-                  Collections.singleton(target_type)
-               )
-            );
-         }
+         RecurrentChecks.assert_can_be_used_as(branch.get_car(), Type.BOOL);
       }
 
-      return new SwitchInstruction(origin, target, branches, default_instruction);
+      return
+         new SwitchInstruction(origin, target, branches, default_instruction);
    }
 
    /**** Accessors ************************************************************/
diff --git a/src/core/src/tonkadur/fate/v1/lang/instruction/While.java b/src/core/src/tonkadur/fate/v1/lang/instruction/While.java
index 6c70025..b29b496 100644
--- a/src/core/src/tonkadur/fate/v1/lang/instruction/While.java
+++ b/src/core/src/tonkadur/fate/v1/lang/instruction/While.java
@@ -1,19 +1,16 @@
 package tonkadur.fate.v1.lang.instruction;
 
-import java.util.Collections;
 import java.util.List;
 
-import tonkadur.error.ErrorManager;
-
 import tonkadur.parser.Origin;
-
-import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.lang.type.Type;
 
 import tonkadur.fate.v1.lang.meta.InstructionVisitor;
 import tonkadur.fate.v1.lang.meta.Instruction;
 import tonkadur.fate.v1.lang.meta.Computation;
+import tonkadur.fate.v1.lang.meta.RecurrentChecks;
 
 public class While extends Instruction
 {
@@ -50,20 +47,9 @@ public class While extends Instruction
       final Computation condition,
       final List<Instruction> body
    )
-   throws InvalidTypeException
+   throws ParsingError
    {
-      if (!condition.get_type().get_base_type().equals(Type.BOOL))
-      {
-         ErrorManager.handle
-         (
-            new InvalidTypeException
-            (
-               condition.get_origin(),
-               condition.get_type(),
-               Collections.singleton(Type.BOOL)
-            )
-         );
-      }
+      RecurrentChecks.assert_can_be_used_as(condition, Type.BOOL);
 
       return new While(origin, condition, body);
    }
diff --git a/src/core/src/tonkadur/fate/v1/lang/meta/RecurrentChecks.java b/src/core/src/tonkadur/fate/v1/lang/meta/RecurrentChecks.java
index da9c233..52fe607 100644
--- a/src/core/src/tonkadur/fate/v1/lang/meta/RecurrentChecks.java
+++ b/src/core/src/tonkadur/fate/v1/lang/meta/RecurrentChecks.java
@@ -1,17 +1,24 @@
 package tonkadur.fate.v1.lang.meta;
 
 import java.util.Collections;
+import java.util.List;
 
 import tonkadur.error.ErrorManager;
 
+import tonkadur.functional.Merge;
+
 import tonkadur.parser.Origin;
 import tonkadur.parser.ParsingError;
 
 import tonkadur.fate.v1.error.ConflictingTypeException;
 import tonkadur.fate.v1.error.IncomparableTypeException;
 import tonkadur.fate.v1.error.InvalidTypeException;
+import tonkadur.fate.v1.error.InvalidArityException;
+import tonkadur.fate.v1.error.SignatureTypeMismatchException;
+import tonkadur.fate.v1.error.IncorrectReturnTypeException;
 
 import tonkadur.fate.v1.lang.type.CollectionType;
+import tonkadur.fate.v1.lang.type.LambdaType;
 import tonkadur.fate.v1.lang.type.Type;
 
 public class RecurrentChecks
@@ -246,4 +253,188 @@ public class RecurrentChecks
          ((CollectionType) c).get_content_type()
       );
    }
+
+   public static void assert_computations_matches_signature
+   (
+      final Origin o,
+      final List<Computation> c,
+      final List<Type> t
+   )
+   throws ParsingError
+   {
+      if (c.size() != t.size())
+      {
+         ErrorManager.handle
+         (
+            new InvalidArityException
+            (
+               o,
+               c.size(),
+               t.size(),
+               t.size()
+            )
+         );
+      }
+
+      try
+      {
+         (new Merge<Type, Computation, Boolean>()
+         {
+            @Override
+            public Boolean risky_lambda (final Type t, final Computation p)
+            throws ParsingError
+            {
+               assert_can_be_used_as(p, t);
+
+               return Boolean.TRUE;
+            }
+         }).risky_merge(t, c);
+      }
+      catch (final ParsingError pe)
+      {
+         throw pe;
+      }
+      catch (final Throwable e)
+      {
+         e.printStackTrace();
+         System.exit(-1);
+      }
+   }
+
+   public static void assert_types_matches_signature
+   (
+      final Origin o,
+      final List<Type> c,
+      final List<Type> t
+   )
+   throws ParsingError
+   {
+      if (c.size() != t.size())
+      {
+         ErrorManager.handle
+         (
+            new InvalidArityException
+            (
+               o,
+               c.size(),
+               t.size(),
+               t.size()
+            )
+         );
+      }
+
+      try
+      {
+         (new Merge<Type, Type, Boolean>()
+         {
+            @Override
+            public Boolean risky_lambda (final Type t, final Type p)
+            throws ParsingError
+            {
+               assert_can_be_used_as(o, p, t);
+
+               return Boolean.TRUE;
+            }
+         }).risky_merge(t, c);
+      }
+      catch (final ParsingError e)
+      {
+         System.err.println(e.toString());
+
+         ErrorManager.handle
+         (
+            new SignatureTypeMismatchException(o, c, t)
+         );
+      }
+      catch (final Throwable e)
+      {
+         e.printStackTrace();
+         System.exit(-1);
+      }
+   }
+
+   public static void assert_is_a_lambda_function (final Computation l)
+   throws ParsingError
+   {
+      if (!(l.get_type() instanceof LambdaType))
+      {
+         ErrorManager.handle
+         (
+            new InvalidTypeException
+            (
+               l.get_origin(),
+               l.get_type(),
+               Collections.singleton(Type.LAMBDA)
+            )
+         );
+      }
+   }
+
+   public static void assert_return_type_is
+   (
+      final Computation l,
+      final Type r
+   )
+   throws ParsingError
+   {
+      try
+      {
+         assert_can_be_used_as
+         (
+            l.get_origin(),
+            ((LambdaType) l.get_type()).get_return_type(),
+            r
+         );
+      }
+      catch (final ParsingError e)
+      {
+         System.err.println(e.toString());
+
+         ErrorManager.handle
+         (
+            new IncorrectReturnTypeException
+            (
+               l.get_origin(),
+               ((LambdaType) l.get_type()).get_return_type(),
+               r
+            )
+         );
+      }
+   }
+
+   public static void assert_lambda_matches_computations
+   (
+      final Computation l,
+      final Type r,
+      final List<Computation> c
+   )
+   throws ParsingError
+   {
+      assert_is_a_lambda_function(l);
+      assert_return_type_is(l, r);
+      assert_computations_matches_signature
+      (
+         l.get_origin(),
+         c,
+         ((LambdaType) l.get_type()).get_signature()
+      );
+   }
+
+   public static void assert_lambda_matches_types
+   (
+      final Computation l,
+      final Type r,
+      final List<Type> c
+   )
+   throws ParsingError
+   {
+      assert_is_a_lambda_function(l);
+      assert_return_type_is(l, r);
+      assert_types_matches_signature
+      (
+         l.get_origin(),
+         c,
+         ((LambdaType) l.get_type()).get_signature()
+      );
+   }
 }