Portability	portable
Stability	stable
Maintainer	http://homepages.nildram.co.uk/~ahey/em.png

Data.COrdering

Contents

Types
Useful combinators
- Misc.
- For combining "equal" values with a user supplied function.

Description

This module defines a useful variant of the Prelude Ordering data type.

Typically this data type is used as the result of a "combining comparison" which combines values that are deemed to be equal (somehow). Note that the functions defined here adhere to the same ordering convention as the overloaded compare (from the Ord class). That is..

 a `compare` b -> LT (or Lt) implies a < b
 a `compare` b -> GT (or Gt) implies a > b

The combinators exported from this module have a "CC" suffix if they return a combining comparison (most of them) and a "C" suffix if they return an ordinary comparison. All the combinators defined here are INLINEd, in the hope that the compiler can avoid the overhead of using HOFs for frequently used comparisons (dunno if this does any good though :-)

Synopsis

Types

data COrdering a Source

Result of a combining comparison.

Constructors

Lt
Eq a
Gt

Instances

Typeable1 COrdering
Eq a => Eq (COrdering a)
Ord a => Ord (COrdering a)
Read a => Read (COrdering a)
Show a => Show (COrdering a)

Useful combinators

Misc.

unitCC :: Ord a => a -> a -> COrdering ()Source

A combining comparison for an instance of Ord which returns unit () where appropriate.

unitByCC :: (a -> b -> Ordering) -> a -> b -> COrdering ()Source

Create a combining comparison from an ordinary comparison by returning unit () where appropriate.

fstCC :: Ord a => a -> a -> COrdering aSource

A combining comparison for an instance of Ord which keeps the first argument if they are deemed equal. The second argument is discarded in this case.

fstByCC :: (a -> b -> Ordering) -> a -> b -> COrdering aSource

Create a combining comparison from an ordinary comparison by keeping the first argument if they are deemed equal. The second argument is discarded in this case.

sndCC :: Ord a => a -> a -> COrdering aSource

A combining comparison for an instance of Ord which keeps the second argument if they are deemed equal. The first argument is discarded in this case.

sndByCC :: (a -> b -> Ordering) -> a -> b -> COrdering bSource

Create a combining comparison from an ordinary comparison by keeping the second argument if they are deemed equal. The first argument is discarded in this case.

flipC :: (a -> b -> Ordering) -> b -> a -> Ordering Source

Converts a comparison to one which takes arguments in flipped order, but preserves the ordering that would be given by the "unflipped" version (disregarding type issues). So it's not the same as using the prelude flip (which would reverse the ordering too).

flipCC :: (a -> b -> COrdering c) -> b -> a -> COrdering cSource

Converts a combining comparison to one which takes arguments in flipped order, but preserves the ordering that would be given by the "unflipped" version (disregarding type issues). So it's not the same as using the prelude flip (which would reverse the ordering too).

For combining "equal" values with a user supplied function.

withCC :: Ord a => (a -> a -> b) -> a -> a -> COrdering bSource

Create a combining comparison using the supplied combining function, which is applied if compare returns EQ. See withCC' for a stricter version of this function.

withCC' :: Ord a => (a -> a -> b) -> a -> a -> COrdering bSource

Same as withCC, except the combining function is applied strictly.

withByCC :: (a -> b -> Ordering) -> (a -> b -> c) -> a -> b -> COrdering cSource

Create a combining comparison using the supplied comparison and combining function, which is applied if the comparison returns EQ. See withByCC' for a stricter version of this function.

withByCC' :: (a -> b -> Ordering) -> (a -> b -> c) -> a -> b -> COrdering cSource

Same as withByCC, except the combining function is applied strictly.