Changes between Version 6 and Version 7 of ExistentialQuantification


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Timestamp:
Dec 2, 2005 11:30:19 PM (10 years ago)
Author:
ross@…
Comment:

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  • ExistentialQuantification

    v6 v7  
    1111data Accum a = forall s. MkAccum s (a -> s -> s) (s -> a)
    1212}}}
     13Constraints are also allowed.
     14
    1315When a value of this type is constructed, `s` will be instantiated to some concrete type. When such a value is analysed, `s` is abstract.
    1416
     
    1820}}}
    1921but see below for alternatives.
     22
     23When pattern matching, the type variable `s` is instantiated to a ''Skolem variable'', which cannot be unified with any other type and cannot escape the scope of the match.
    2024
    2125== References ==
     
    8286
    8387== Pros ==
    84  * offered by GHC and Hugs for over 15 years, HBC even longer and also by Nhc98.
     88 * offered by GHC, Hugs and Nhc98 for years, HBC even longer.
     89 * typing rules well understood.
    8590 * quite handy for representations that delay composition or application, e.g. objects, various parser combinator libraries from Utrecht.
    8691