[Hackage] #376: Allow constraint on using installed package versions

[Hackage]

#376: Allow constraint on using installed package versions
---------------------------------+------------------------------------------
  Reporter:  duncan              |        Owner:        
      Type:  enhancement         |       Status:  new   
  Priority:  normal              |    Milestone:        
 Component:  cabal-install tool  |      Version:  HEAD  
  Severity:  normal              |   Resolution:        
  Keywords:                      |   Difficulty:  normal
Ghcversion:  6.8.3               |     Platform:        
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Comment (by duncan):

 This is now supported internally. We just need a way to pass the
 constraints in via the command line interface.

 I'm thinking of using:
 {{{
 cabal install foo --constraint="bar installed"
 }}}

 which mirrors the existing:
 {{{
 cabal install foo --constraint="bar >= 1.2"
 }}}

 and similarly we could add flags constraints for particular packages:
 {{{
 cabal install foo --constraint="bar +gtk -vty"
 }}}

 but perhaps flags want a different approach. Suggestions welcome.

-- 
Ticket URL: <http://hackage.haskell.org/trac/hackage/ticket/376#comment:4>
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