The Eval plugin evaluates code inserted in comments.

This is mainly useful to test and document functions and to quickly
evaluate small expressions.

Every line of code to be evaluated is introduced by >>>

A quick calculation:

-- >>> 2**4.5/pi
-- 7.202530529256849

A little test for the double function:

{- |
A doubling function.

>>> double 11
22
-}
double = (2*)