read-bounded-0.1.1.0: Class for reading bounded values

Safe HaskellSafe-Inferred
LanguageHaskell2010

Text.Read.Bounded

Synopsis

Documentation

data BoundedRead a

Information about a bounded read.

Constructors

NoRead

The read failed.

ExactRead a

The value was successfully read exactly, and did not have to be clamped to a narrower representation.

ClampedRead a

The value was successfully read, but had to be clamped to a narrower representation because its value was too wide.

Instances

Eq a => Eq (BoundedRead a) 
Ord a => Ord (BoundedRead a) 
Read a => Read (BoundedRead a) 
Show a => Show (BoundedRead a) 

class ReadBounded a where

Much like the Read class, but will return (possibly) clamped values.

Typical instances of this class will clamp against minBound and maxBound

This class is designed to avoid inconsistency problems such as the following:

>>> read "321" :: Word8
65

>>> read "4321" :: Word8
225

>>> read "-4" :: Word8
252

Using this class, the results are predictable and precise:

>>> readBounded "321" :: BoundedRead Word8
ClampedRead 255

>>> readBounded "4321" :: BoundedRead Word8
ClampedRead 255

>>> readBounded "-4" :: BoundedRead Word8
ClampedRead 0

>>> readBounded "255" :: BoundedRead Word8
ExactRead 255

>>> readBounded "6" :: BoundedRead Word8
ExactRead 6

>>> readBounded "xxx" :: BoundedRead Word8
NoRead

readBoundedInteger :: (Bounded a, Read a, Integral a) => String -> BoundedRead a

Reads a clamped value for any integer type with the given class constraints. Useful for implementing a ReadBounded instance or avoiding one.