`Unit` Statement

Identifies a unit of measure.

Syntax

Usual construct

[ @SI [ prefix_type ] ] _
Unit unit_names [ = expression ]

Interval-scale construct

Unit unit_names ( parameter In unit ) = expression

Parts

@SI

Optional indication of an SI (metric) unit.

prefix_type

Optional after @SI, one of these identifiers:

BINARY – Gives these prefixes: kibi or Ki (2^¹⁰), mebi or Mi (2^²⁰), gibi or Gi (2^³⁰), tebi or Ti (2^⁴⁰), pebi or Ti (2^⁵⁰), exbi or Ei (2^⁶⁰), zebi or Zi (2^⁷⁰), yobi or Yi (2^⁸⁰).
LARGE – Gives these prefixes: deca or deka or da (10^¹), hecto or h (10^²), kilo or k (10^³), mega or M (10^⁶), giga or G (10^⁹), tera or T (10^¹²), peta or P (10^¹⁵), exa or E (10^¹⁸), zetta or Z (10^²¹), yotta or Y (10^²⁴), ronna or R (10^²⁷), quetta or Q (10^³⁰).
SMALL – Gives these prefixes: deci or d (10^⁻¹), centi or c (10^⁻²), milli or m (10^⁻³), micro or µ or μ or u (10^⁻⁶), nano or n (10^⁻⁹), pico or p (10^⁻¹²), femto or f (10^⁻¹⁵), atto or a (10^⁻¹⁸), zepto or z (10^⁻²¹), yocto or y (10^⁻²⁴), ronto or r (10^⁻²⁷), quecto or q (10^⁻³⁰).

If not supplied, the default prefixes are those given by LARGE and small put together.

unit_names

Mandatory one or more names with spaces between each. All names identify the same unit.

Unit name

[ number ] { name | name + suffix | prefix - name }

name

Mandatory basic name for a unit of measure.

number

One of the integer literals that follow:

1 – name is irregular and grammatically singular. For example, «1 foot».
2 – name is irregular and grammatically plural. For example, «2 feet».
0 – name is grammatically singular for zero and one. This occurs in some languages, for example, French. You can use 0 (and no others) with suffix or prefix.

suffix

Mandatory after +. Identifies the regular plural suffix for name. For example, «metre+s» or «inch+es».

prefix

Mandatory before a hyphen (-). Identifies the regular plural prefix for name. This occurs in some languages, most frequently in Africa. For example, in Swahili, «ma-debe».

expression

A conversion factor.

Optional in the usual construct.

Mandatory in the interval-scale construct.

parameter

Mandatory in the interval-scale construct. You use it with expression for a unit with an interval scale, for example, a unit of temperature.

unit

A different unit that is related to this unit.

Instructions

TODO

Examples

// Make meter, metres, kilometer, millimetres, m, km, mm ...
@SI Unit meter+s metre+s m

// Derived unit.
Unit light_year+s ly = 9.4605284 petameters

// in. is not permitted because IN is a keyword
// and a name cannot have a period,
// but you can write IN between backticks.
Unit inch+es `in` = 2.54 cm

// Kelvin cannot be plural.
Unit Kelvin K

// °C is not given because it is not easy to write.
// 1 makes a singular name and 2 makes a plural name.
// This is an interval-scale unit, thus the parameter k.
Unit Celsius 1 degree_C 2 degrees_C (k In Kelvin) = k + 273.15

// Make second, secs, milliseconds, s, ms, ...
@SI SMALL Unit second+s sec+s s

// Make byte, kibibytes, mebibyte, B, KiB, MiB, ...
// Does not permit Kilobyte, megabytes, KB, MB, ...
@SI BINARY Unit byte+s B

Unit Statement