How do I implement a parser for this example from grep --help:
--binary-files=TYPE assume that binary files are TYPE;
TYPE is 'binary', 'text', or 'without-match'
Assuming that I have
data BinaryFiles = Binary | Text | WithoutMatch
How do I write a parser? option auto seems a kludge since Read is supposed to be an "inverse" to Show, and I'd like to keep the derived instance Show BinaryFiles.