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 -v2, except that in addition the full command line (if appropriate) for each compilation phase is also printed.
The same as -v3 except that the intermediate program representation after each compilation phase is also printed (excluding preprocessed and C/assembly files).
Print a one-line string including GHC's version number.
Print GHC's numeric version number only.
Print the path to GHC's library directory. This is the top of the directory tree containing GHC's libraries, interfaces, and include files (usually something like /usr/local/lib/ghc-5.04 on Unix). This is the value of $libdirin the package configuration file (see Section 4.8).