Documentation

DarcsOption instantiates the first two type parameters of OptSpec to what we need in darcs.

This is PrimOptSpec instantiated with DarcsOptDescr and Flag.

We do not instantiate the d in OptSpec d f directly with OptDescr. Instead we (post-) compose it with (->) AbsolutePath. Modulo newtype noise, this is the same as

 type DarcsOptDescr f = OptDescr (AbsolutePath -> f)

This is so we can pass a directory relative to which an option argument is interpreted (if it has the form of a relative path).

Instantiate a DarcsOptDescr with an AbsolutePath