4.4. Help and verbosity options  ––help, -?  Cause GHC to spew a
long usage message to standard output and then exit.   The -v
option makes GHC verbose: it reports its version number and
shows (on stderr) exactly how it invokes each phase of the
compilation system. Moreover, it passes the -v flag to most
phases; each reports its version number (and possibly some other
information).  Please, oh please, use the -v option when
reporting bugs! Knowing that you ran the right bits in the right
order is always the first thing we want to verify.   To provide
more control over the compiler's verbosity, the -v flag takes an
optional numeric argument. Specifying -v on its own is
equivalent to -v3, and the other levels have the following
meanings:   Disable all non-essential messages (this is the
default).   Minimal verbosity: print one line per compilation
(this is the default when ––make or ––interactive is on).
Print the name of each compilation phase as it is executed.
(equivalent to -dshow-passes).   The same as -