russelldavies/elm-range

Model and operate on a range of values in Elm.

Result.map2 Range.merge
    (Range.fromString Range.types.int "[1,5]")
    (Range.fromString Range.types.int "(4,10]")
    |> Result.map Range.toString -- Ok "[1,11)"

Overview

The concept of a range is inspired from PostgreSQL's Range Types:

Range types are data types representing a range of values of some element type (called the range's subtype). For instance, ranges of timestamp might be used to represent the ranges of time that a meeting room is reserved. In this case the data type is tsrange (short for “timestamp range”), and timestamp is the subtype. The subtype must have a total order so that it is well-defined whether element values are within, before, or after a range of values.

Range types are useful because they represent many element values in a single range value, and because concepts such as overlapping ranges can be expressed clearly. The use of time and date ranges for scheduling purposes is the clearest example; but price ranges, measurement ranges from an instrument, and so forth can also be useful.

Usage

When creating a range, either from a string or directly from values, you will need to specify a type. This library provides a few for Int, Float, String, and Time.Posix in the Range.types record. If you need a custom one, you will need to write your own TypeConfig (essentially a typeclass).