Hello Haskellers, Björn Buckwalter and I are pleased to announce the release to Hackage of version 1.0 of the dimensional library, which statically tracks physical dimensions in Haskell code, as in the example below, preventing dimensional mistakes and requiring explicit documentation of units where raw values are exchanged with external systems. {-# LANGUAGE NoImplicitPrelude #-} module Example where import Numeric.Units.Dimensional.Prelude import Numeric.Units.Dimensional.NonSI -- a function that computes with dimensional values escapeVelocity :: (Floating a) => Mass a -> Length a -> Velocity a escapeVelocity m r = sqrt (two * g * m / r) where two = 2 *~ one g = 6.6720e-11 *~ (newton * meter ^ pos2 / kilo gram ^ pos2)
let re = 6372.792 *~ kilo meter let me = 5.9742e24 *~ kilo gram let ve = escapeVelocity me re ve -- Show defaults to SI base units 11184.537332296259 m s^-1 showIn (mile / hour) ve -- but we can show in other units "25019.09746845083 mi / h" let vekph = ve /~ (kilo meter / hour) -- and extract raw values when needed 40264.33439626653
This version is a major upgrade, consolidating features from the classic dimensional package and the dimensional-tf package. It takes advantage of the DataKinds and ClosedTypeFamilies extensions in GHC 7.8 to offer even safer types with a nearly identical interface. Also included: - Units carry names which can be combined by multiplication, division, and (only where appropriate) application of metric prefixes. You can use expressions like: showIn (milli meter / second) timeTravelSpeed to get "39339.52 mm / s" - Exact conversion factors between units are available, even when those conversion factors involve multiples of pi, thanks to the exact-pi library - The dimensionally-polymorphic siUnit term represents the coherent SI base unit of any dimension, which can be convenient for wrapping and unwrapping quantities in some contexts. - Storable and Unbox instances for Quantity types are available thanks to the efforts of Alberto Valverde González. - The Numeric.Units.Dimensional.Dynamic module offers types for safely manipulating quantities and units whose dimensions are not known statically. Also available is a term-level representation for dimensions. - Several other missing instances have been provided, including Bounded, Data, and Typeable instances. - New commonly used US customary units have been added, including US fluid measures and the knot. We have several other development efforts underway, including a type-checker plugin inspired by Adam Gundry's work, and on which he has provided valuable advice, which we hope will lead to a clean library for dimensionally typed linear algebra. Comments and contributions are welcome at http://github.com/bjornbm/dimensional-dk. (The repository name is a carryover from the name we were using while developing this version.) One particularly welcome contribution would be assistance with developing a patch for GHC issue 10391 https://ghc.haskell.org/trac/ghc/ticket/10391. Cheers, Doug McClean