[darcs-devel] darcs patch

[Juliusz Chroboczek]

Thu Sep 16 08:58:29 CEST 2004  Juliusz Chroboczek <jch at pps.jussieu.fr>
  * Make _darcs/current polymorphic.
  This allows multiple formats for _darcs/current.  Currently, two
  formats are implemented:
  
    - PlainCurrent, the directory _darcs/current that we all know and love;
    - NoCurrent, just a placeholder file _darcs/current.none.
  
  A third format, HashedCurrent, is planned but not implemented yet
  (there are stubs in Current.lhs).
  
  You can convert to the NoCurrent format by doing
  
    $ rm -r _darcs/current
    $ touch _darcs/current.none
  
  and convert back to PlainCurrent by doing
  
    $ rm _darcs/current.none
    $ mkdir _darcs/current
    $ darcs repair
  
  There are two problems with this code that I was unable to solve.
  First, getCurrentPop in Population.lhs is a gross violation of
  modularity; it is actually the only reason why Current is not abstract
  (it has to export PlainCurrent).  Second, surely_slurp_Current in
  Repository.lhs leaves a temporary directory after darcs terminates;
  we're bitten by the laziness of slurp.  These problems should be
  solved before release.
  
  Converting Current to be a type class instead of an algebraic
  datatype is left as an exercice for the reader (hint: you need
  existential types).

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