Changes between Version 1 and Version 2 of ClassSystem

Timestamp:

04/18/06 01:42:49 (7 years ago)

Author:

ross@…

Comment:

--

ClassSystem

@@ -15 +15 @@
 These are the proposals that seem to have some support.
 
- * #32  add FlexibleInstances   
- * #31  add FlexibleContexts    
+ * #32  add FlexibleInstances
+
+ MultiParamTypeClasses and TypeSynonymInstances are little use without generalizing the form of instances.
+ The proposal is to generalize but retain guaranteed termination of instance inference via (necessarily conservative) syntactic restrictions.
+
+ * #31  add FlexibleContexts
+
+ With FlexibleInstances, more contexts become irreducible.
+
  * #70  allow TypeSynonymInstances      
  * #17  relax restriction on signatures of class methods        
  * #81  scoping of type variables in class instances
+
+ An opportunity for ScopedTypeVariables that is already present in the syntax.
+
  * #52  Generalised deriving for newtype
 
@@ -39 +49 @@
  * #54  add overlapping or incoherent instances 
       
- Overlapping instances add complexity to an already difficult problem. With overlapping instances:
-   * Haskell would need to be a lot more specific about exactly where context reduction takes place. 
-   * A program that type checks can have its meaning changed by adding an instance declaration
-   * Similarly adding "import M()" can change the meaning of a program (by  changing which instances are visible
-   * When exactly is overlap permitted?  Is this ok?
-    {{{    
-           instance C a Int
-           instance C Bool b
-    }}}
+ [wiki:OverlappingInstances Overlapping instances] add complexity to an already difficult problem, [wiki:IncoherentInstances incoherent instances] even more so.
+
  * #18  add closed classes
  * #19  control export and import of class instances    
@@ -63 +66 @@
  * #14  add Associated Types (ATs)
 
-The bottom line is that Haskell' should have multiparameter type
+'''Proposal:''' Haskell' should have multiparameter type
 classes and functional dependencies. Multiparameter type classes are
 useful for programming, and something like functional dependencies are