collections-0.3.1: Useful standard collections types and related functions.







class Ord a => DiscreteOrdered a whereSource

Distinguish between dense and sparse ordered types. A dense type is one in which any two values v1 < v2 have a third value v3 such that v1 < v3 < v2.

In theory the floating types are dense, although in practice they can only have finitely many values. This class treats them as dense.

Tuples up to 4 members are declared as instances. Larger tuples may be added if necessary.

This approach was suggested by Ben Rudiak-Gould on comp.lang.functional.


adjacent :: a -> a -> BoolSource

Two values x and y are adjacent if x < y and there does not exist a third value between them. Always False for dense types.

enumAdjacent :: (Ord a, Enum a) => a -> a -> BoolSource

Check adjacency for sparse enumerated types (i.e. where there is no value between x and succ x). Use as the definition of adjacent for most enumerated types.

boundedAdjacent :: (Ord a, Enum a) => a -> a -> BoolSource

Check adjacency, allowing for case where x = maxBound. Use as the definition of adjacent for bounded enumerated types such as Int and Char.

data Boundary a Source

A Boundary is a division of an ordered type into values above and below the boundary. No value can sit on a boundary.

Known bug: for Bounded types

  • BoundaryAbove maxBound < BoundaryAboveAll
  • BoundaryBelow minBound > BoundaryBelowAll

This is incorrect because there are no possible values in between the left and right sides of these inequalities.


BoundaryAbove a

The argument is the highest value below the boundary.

BoundaryBelow a

The argument is the lowest value above the boundary.


The boundary above all values.


The boundary below all values.

above :: Ord v => Boundary v -> v -> BoolSource

True if the value is above the boundary, false otherwise.

(/>/) :: Ord v => v -> Boundary v -> BoolSource

Same as above, but with the arguments reversed for more intuitive infix usage.