Changes between Version 8 and Version 9 of TypeFunctions/ClassFamilies


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Timestamp:
May 16, 2007 1:16:05 PM (7 years ago)
Author:
simonpj
Comment:

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  • TypeFunctions/ClassFamilies

    v8 v9  
    4646The class-family instances have no members in this case, but use existing classes as a superclass to supply `insert` with the equality and ordering methods, respectively.  As we want to use these superclasses for sets of any element type of which we have an instance of the superclasses, we need a catch-all instance  for each class instance (the "tiresome instances" avove).  That is somewhat ugly especially, as it requires the use of `-fallow-undecidable-instances`.  Furthermore, if the class has no signatures, there is no other useful instance we could possibly give. 
    4747 
    48 SLPJ note: I wonder whether it is ever useful to have a class instance with signatures.  Suppose we only allowed the signature-free form?  That would simplify the explanation in many ways (e.g. no need to say whether class instances can themselves have assoicated types!), and loses no expressive power.  I don't think it loses much convenience either. 
     48'''SLPJ note''': I wonder whether it is ever useful to have a class instance with signatures?  Suppose we only allowed the signature-free form?  That would simplify the explanation in many ways (e.g. no need to say whether class instances can themselves have assoicated types!), and loses no expressive power.  I don't think it loses much convenience either. 
    4949 
    5050=== The language extension === 
     
    142142  type Element [a] = a 
    143143}}} 
     144'''SLPJ note''': I don't understand the question here.