Examples of τ being used in the real world

active Haskell library

https://hackage.haskell.org/package/active-0.1.0.6/docs/Data-Active.html

or example, to create a value of type Active Double which represents one period of a sine wave starting at time 0 and ending at time 1, we could write mkActive 0 1 (\t -> sin (fromTime t * tau)) or (sin . (*tau)) <$> ui.

diagrams Haskell library

Diagrams

https://diagrams.github.io/doc/vector.html

  example = lwG 0.05 . mconcat . map fromOffsets
          $ [ [r *^ e (r @@ rad)]
            | r <- [33 * tau/32, 34 * tau/32 .. 2 * tau]
            ]