module `unit`

The unit module is a module that defines units that are often used in numerical calculations as types. Erg numeric types include Nat, Int, Ratio, and so on. However, these types do not have information about "what the numbers mean", so nonsense calculations such as adding meters and yards can be performed. By using the unit module, you can avoid mistakes such as passing numbers with different units to functions. Mistakes like this actually occur, and serious bugs such as Mars probe missing due to wrong unit system can cause it. You should use this module if you want your code to be more robust when doing numerical computations.

{*} = import "unit"

x = 6m # equivalent to `x = Meter.new(6)`
t = 3s # equivalent to `t = Sec.new(3)`
# m/s is a velocity unit object, of type Velocity
print! x/t # 2m/s
print! x + 4m # 10m
print! x + 2s # TypeError: `+`(Meter, Sec) is not implemented

The objects m, s, and m/s are called unit objects. It has the meaning of 1m, 1s, 1m/s by itself. m/s can be said to be a unit object created by combining m and s.

In unit, the following units are defined as types. It is called SI (International System of Units).

Length: Meter (unit constant: m)
Mass: KiloGram (unit constant: kg, g = 0.001kg)
Time: Sec (minute, hour, day, year, etc. have constants such as minute, hour, day, year generated from Sec)
Current: Amper (unit constant: a)
Temperature: Kelvin (unit constant: k, Fahren, Celsius types are also available and can be converted to each other)
Amount of substance: Mol (unit constant: mol)
Luminous intensity: Candela (unit constant: cd)

In addition, the types Unit1, UnitMul, and UnitDiv are defined, which can be used to create new units by combining basic types. For example, UnitDiv(Unit1, Sec), because the unit of frequency hertz (hertz) is defined as the reciprocal of the vibration period (seconds). If you want to treat this type as a meaningful type (such as adding a dedicated method), you should create a patch.

Hertz = Patch UnitDiv(Unit1, Sec)
SquareMeter = Patch UnitMul(Meter, Meter)

Some auxiliary units are also predefined.

Frequency: Hertz(hz)
Force: Newton(newton)
Energy: Joule(j)
Power: Watt(w)
Potential: Volt(v)
Electrical resistance: Ohm(ohm)
Velocity: Velocity(m/s)
Area: SquareMeter(m^2)
Volume: CubicMeter(m^3) (liter = 10e-3 m^3)
Angle: Degree(deg) (rad = 180/pi deg)
Length: Feet, Yard, Inch, Mile, Ly, Au, Angstrom
Weight: Pound

It also defines a prefix.

Femto = 1e-15
Pico = 1e-12
Nano = 1e-9
Micro = 1e-6
Milli = 1e-3
Centi = 1e-2
Deci = 1e-1
Hecto = 1e+2
Kilo = 1e+3
Mega = 1e+6
Giga = 1e+9
Tera = 1e+12
Peta = 1e+15
Exa = 1e+18

*Contrary to the origin of the name, Erg basically adopts the MKS unit system. If you want the unit module of the CGS unit system, please use an external library (cgs etc.).

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module unit

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Raw Blame History

module `unit`