:set command sets two types of options: GHCi options, which
begin with +’, and “command-line” options, which begin with ‘-’.
NOTE: at the moment, the doesn't support any kind of quoting in
its arguments: quotes will not be removed and cannot be used to
group words together. For :set -DFOO='BAR BAZ' will not do what
GHCi options may be set using The available GHCi options are:
Normally, any evaluation of top-level expressions (otherwise
known as CAFs or Constant Applicative Forms) in loaded modules
is retained between evaluations. Turning +r causes all
evaluation of top-level expressions to be discarded after each
evaluation (they are still retained during a single evaluation).
This option may help if the evaluated top-level expressions are
consuming large amounts of space, or if you need repeatable
performance measurements. Display some stats after evaluating
each expression, including the elapsed time and number of bytes
allocated. NOTE: the allocation figure is only accurate to the
size of the storage manag