d10-0.1.0.1: README.md

# d10

Data types representing the digits zero through nine.

## Modules

Each of the following modules defines a different type named
`D10`, all of which are different representations of the same
concept:

* `Data.D10.Char` - Defines a `D10` type as a newtype for `Char`,
  where the values are restricted to characters between `'0'` and
  `'9'`.
* `Data.D10.Num` - Defines a `D10` type as a newtype for any
  type with an instance of the `Num` class, where the values
  are restricted to numbers between `fromInteger 0` and
  `fromInteger 9`.
* `Data.D10.Safe` - Defines a `D10` type as
  `D0 | D1 | D2 | ... | D9`.

Other modules:

* `Data.D10.Predicate` - Functions to test whether values of
  various types represent digits in the range *0* to *9*.

## Quasi-quoters

Each module that defines a `D10` type also defines quasi-quoters
for it. With the `QuasiQuotes` GHC extension enabled, a single
digit like *7* can be written as `[d10|7|]`, and a list of digits
like *[4,5,6]* can be written as `[d10|456|]`. For `Data.D10.Char`
and `Data.D10.Num`, the quasi-quoters are an important feature,
because the `D10` types defined in these modules have unsafe
constructors, and the quasi-quoters provide compile-time assurance
that we never construct a `D10` that represents a value outside
the range *0* to *9*. For `Data.D10.Safe`, the quasi-quoter is
offered merely as a possible convenience, allowing you to write
`[d10|456789|]` in place of the somewhat longer expression
`[D4,D5,D6,D7,D8,D9]`.