RepLib-0.2.1: Generic programming library with representation typesSource codeContentsIndex

The module PreludeLib contains generic operations to derive members of the standard prelude classess: Eq, Bounded, Compare, Show (TODO: add Enum and Read)

Although these classes may already be automatically derived via the deriving mechanism, this module is included for two reasons:

  • Deriving only works when datatypes are defined. This library allows instances of these classes to be generated anywhere. For example, suppose some other module contains the definition of the datatype T and exposes all of its constructors, but, frustratingly, does not derive an instance of the Show class.

You could define a Show instance of T in your own module with the following code:

 import RepLib  

 (repr1 ''T)  -- make the Rep1 instance of T available

 instance Show T where
   showsPrec = showsPrecR1 rep1   -- showsPrecR1 is defined in this module
  • This library also serves as a model for generic functions that are slight modifications to these prelude operations. For example, if you wanted to define reverse lexicographic ordering or an XML pretty printer for datatypes, you might start here. This library is also a good place to start learning how to define your own generic operations, because the behavior of these operations should match the deriving mechanism specified by Haskell 98.
data EqD a
eqR1 :: R1 EqD a -> a -> a -> Bool
data OrdD a
compareR1 :: R1 OrdD a -> a -> a -> Ordering
data BoundedD a
minBoundR1 :: R1 BoundedD a -> a
maxBoundR1 :: R1 BoundedD a -> a
data ShowD a
showsPrecR1 :: R1 ShowD a -> Int -> a -> ShowS
data EqD a Source
show/hide Instances
Eq a => Sat (EqD a)
eqR1 :: R1 EqD a -> a -> a -> BoolSource
Polymorphic equality, given an R1 representation
data OrdD a Source
show/hide Instances
Ord a => Sat (OrdD a)
compareR1 :: R1 OrdD a -> a -> a -> OrderingSource
Minimal completion of the Ord class
data BoundedD a Source
show/hide Instances
minBoundR1 :: R1 BoundedD a -> aSource
To generate the Bounded class
maxBoundR1 :: R1 BoundedD a -> aSource
To generate the Bounded class
data ShowD a Source
show/hide Instances
Show a => Sat (ShowD a)
showsPrecR1 :: R1 ShowD a -> Int -> a -> ShowSSource
Minimal completion of the show class
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