Safe Haskell	Safe

Data.Prefix.Units

Contents

Basic definitions
- Types
- Unit-related functions
Formatting functions
Parsing functions
Low-level generic functions
- Parsing
- Formatting

Description

Definitions and functions for parsing and formatting prefix units.

This module defines the type Unit and associated functions for parsing numbers containing a prefix unit (e.g. 100M) into corespondingly scaled values (for the above example, 100000000), and for formatting numbers.

The units definition is taken from the man page units(7) and the web sites http://physics.nist.gov/cuu/Units/prefixes.html and http://physics.nist.gov/cuu/Units/binary.html.

Since a give prefix unit (e.g. m) can be interpreted in different ways, the module offers various ways to interpret this:

in a binary context (e.g. when talking about memory), this will be interpreted as 2^20 (see ParseBinary)
in a SI context dealing with multiples, this will be intepreted as 10^3 (see ParseKMGT)
in an exact parsing mode, this will be interpreded as the "milli" prefix, i.e. 10^-3 (see ParseExact)

The different parsing mode are offered as different contexts will have different "natural" units, and always forcing precise parsing (which also implies case-sensitivity) will lead to confusing user interfaces.

The internal calculations when converting values are done via the Rational type (with arbitrary precision), and precision loss happens only at the last step of converting to the target type; for float/doubles this is fromRational, for integral types this is round.

A few examples are given below:

>>> showValue (Left FormatBinary) 2048
"2.0Ki"
>>> showValue (Left FormatSiAll) 0.0001
"100.0u"
>>> showValue (Right Mebi) 1048576
"1Mi"
>>> parseValue ParseExact "2.5Ki"::Either String Double
Right 2560.0
>>> parseValue ParseBinary "2M"::Either String Int
Right 2097152
>>> parseValue ParseExact "2ki"
Left "Unrecognised unit 'ki'"

The failure in the last example is due to the fact that ParseExact is case-sensitive.

Synopsis

Basic definitions

Types

data Unit Source

The unit type.

Constructors

Yocto
Zepto
Atto
Femto
Pico
Nano
Micro
Milli
Centi
Deci
Deka
Hecto
Kilo
Kibi
Mega
Mebi
Giga
Gibi
Tera
Tebi
Peta
Pebi
Exa
Exbi
Zetta
Yotta

Instances

Bounded Unit
Enum Unit
Eq Unit
Ord Unit
Show Unit

class Real a => RationalConvertible a whereSource

Typeclass for handling values that can be converted to/from Rational.

Methods

convFromRational :: Rational -> aSource

Converts the value from Ratioal

Instances

RationalConvertible Double
RationalConvertible Float
RationalConvertible Int
RationalConvertible Integer
RationalConvertible Rational

siUnits :: [Unit]Source

List of all SI units.

siSupraunitary :: [Unit]Source

List of units which are supraunitary (their multiplier is greater than one).

siKMGT :: [Unit]Source

List of SI units which are greater or equal to Kilo.

binaryUnits :: [Unit]Source

List of binary units.

Unit-related functions

unitMultiplier :: Unit -> Rational Source

Returns the unit scaling "multiplier" (which can be either supra- or sub-unitary):

>>> unitMultiplier Micro
1 % 1000000
>>> unitMultiplier Mebi
1048576 % 1

unitName :: Unit -> String Source

Returns the unit full name.

unitSymbol :: Unit -> String Source

Returns the unit ASCII symbol.

fancySymbol :: Unit -> String Source

Returns the unit symbol, which for the Micro unit is not ASCII.

Formatting functions

data FormatMode Source

Defines the formatting modes.

Constructors

FormatSiAll	Formats the value using any SI unit.
FormatSiSupraunitary	Formats the value using supraunitary SI units only (which means that e.g. `0.001` will remain as such instead of being formatted as `1m`)
FormatSiKMGT	Formats the value using units greater or equal to `Kilo`.
FormatBinary	Formats the value using binary units.

Instances

Bounded FormatMode
Enum FormatMode
Show FormatMode

recommendedUnit :: Real a => FormatMode -> a -> Maybe Unit Source

Computes the recommended unit for displaying a given value. The simple algorithm uses the first unit for which we have a supraunitary representation. In case we don't find any such value (e.g. for a zero value), then Nothing is returned.

formatValue Source

Arguments

:: RationalConvertible a
=> FormatOption	The desired `FormatMode` or `Unit`
-> a	The value to format
-> (a, Maybe Unit)	Scaled value and optional unit

Computes the scaled value and unit for a given value

showValue Source

Arguments

:: (RationalConvertible a, Show a)
=> FormatOption	The desired format mode, either as a `Left` `FormatMode` value which computes the unit automatically, or as a `Right` `Unit`, which will use the specified unit
-> a	The value to show
-> String	Resulting string

Generates a final string representation of a value.

Parsing functions

data ParseMode Source

Defines available parse modes.

Constructors

ParseExact	Exact parser mode. This mode is fully case-sensitive.
ParseKMGT	Parses only units bigger than `Kilo`, respectively `Kibi` (for binary units). This allows the parser to be case-insensitive.
ParseBinary	Parses binary units only. In this mode, both the exact and shortened forms are accepted (e.g. both "k" and "ki" will be converted into `Kibi`). Furthermore, the parsing is case-insensitive.

Instances

Bounded ParseMode
Enum ParseMode
Show ParseMode

parseSymbol :: ParseMode -> String -> Either String Unit Source

Parses a unit from a string. The exact parsing mode determines the rules for parsing and the range of possible units.

parseValue Source

Arguments

:: (Read a, RationalConvertible a)
=> ParseMode	The desired parse mode
-> String	String to be parsed
-> Either String a	Either a Left error message, or a Right parsed value

Main parse routine.

Low-level generic functions

unitRange :: FormatMode -> [Unit]Source

The available units range for various format modes.

Parsing

data ParseOptions Source

Defines unit handling mode on parse.

Constructors

UnitRequired	Requires that the input string has a unit.
UnitDefault Unit	If unit is missing, use a default one.
UnitOptional	The unit is optional, a missing one means the value is not scaled.

Instances

Show ParseOptions

parseExactSymbol :: String -> Either String Unit Source

Parses a symbol in the exact mode. See ParseExact for details.

parseBinarySymbol :: String -> Either String Unit Source

Parses a binary symbol. See ParseBinary for details.

parseKMGTSymbol :: String -> Either String Unit Source

Parses the given symbol as one of the "big" units (kilo/kibi and above). This allows the parsing to be case-insensitive.

parseGeneric Source

Arguments

:: (Read a, RationalConvertible a)
=> ParseOptions	Unit options
-> [Unit]	Optional list of valid units
-> ParseMode	The desired parse mode
-> String	String to be parsed
-> Either String a

Low-level parse routine. Takes two function arguments which fix the initial and final conversion, a parse mode and the string to be parsed.

Formatting

showValueWith Source

Arguments

:: (RationalConvertible a, Show a)
=> (Unit -> String)	Function to convert the (optional) unit into a string, e.g. `unitSymbol` or `fancySymbol`
-> FormatOption	The desired format mode
-> a	The value to show
-> String	Resulting string

Simple helper to generate the full string representation of an integral value.