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Library for handing quantities with units.

Adding new Unit Types and Units

There are several files that need to be updated to include a new unit type, or a new unit for an existing type.

New Unit Type (e.g. pressure)

  • Identify the base unit, most likely an SI unit (e.g. pascals). All quantities for this unit type will be converted to this SI unit.
  • The base unit quantities must be compatible with each other. For instance, 1 meter divided by 1 second is 1 meter-per-second.
    • Can a test be added for this? What happens if this rule is broken?
  • Add it to si-units in core.cljc (e.g. :pressure “pascals”)
  • Add any allowed-operations in core.cljc
    • How is it related to other unit types? (e.g. (division :pressure :force :area))
  • If the unit type doesn’t follow normal math rules (e.g. like angles), this it can’t be added to core.cljc and will require a new namespace with a new deftype and separate math implementations. See angles.cljc.

New Units (e.g. atmospheres, mmHg)

  • Identify the unit-type (e.g. pressure). Implement the new unit type if necessary.
  • If it’s not a base/SI unit, add the conversion constants and functions to/from in units.cljc.
    • Conversions to/from non-base units is not required for quantus, but may be convenient for anyone using the conversions directly.
  • Add the function to create a quantity and extract the value in core.cljc. Remember to put the correct conversion function and unit type. If it’s a base/SI unit, then you don’t need the unit conversions.
(defn millimeters-Mercury [v] (Quantity. (u/millimeters-Mercury->pascals v) :pressure))
(defn ->millimeters-Mercury [^Quantity q] (assert-unit-type q :pressure) (u/pascals->millimeters-Mercury (get-value q)))
  • Add the new unit to data_readers.cljc.
  • Add the new unit to the units-list in core_test.cljc. This will add it to the suite of tests performed on each unit type, as well as every pair of unit types.
    • Note that units that have an offset (like temperature) will need to be skipped for some tests (celsius and fahrenheit are already excluded from some tests, so add it there).
  • Run the tests lein test and npx shadow-cljs release test

Copyright and License

Copyright © 2021 7theta

Distributed under the MIT License.

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