Multiplies two Quantitys or two Units.
The intimidating type signature captures the similarity between these
operations and ensures that composite Units are
NonMetric.
The product of two type-level numbers.
Due to changes in GHC 8.6, using this operator infix and unqualified
requires the NoStarIsType language extension to be active. See the GHC
8.6.x migration guide for details:
https://ghc.haskell.org/trac/ghc/wiki/Migration/8.6