Changes between Version 6 and Version 7 of ExistentialQuantification


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Timestamp:
Dec 2, 2005 11:30:19 PM (8 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