[GHC] #10874: Implement `:type-at`, `:all-types`, `:loc-at` in GHCi

[GHC]

#10874: Implement `:type-at`, `:all-types`, `:loc-at` in GHCi
-------------------------------------+-------------------------------------
        Reporter:  hvr               |                Owner:
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:  8.0.1
       Component:  GHCi              |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1240
-------------------------------------+-------------------------------------

Comment (by Herbert Valerio Riedel <hvr@…>):

 In [changeset:"2f6e87a494330837c425dab67ba26ee36bd9eacf/ghc"
 2f6e87a4/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="2f6e87a494330837c425dab67ba26ee36bd9eacf"
 Introduce HasGhciState class and refactor use-sites

 This allows to reach the GhciState without having to keep
 track how many Monad transformer layers sit on top of the
 GHCi monad.

 While at it, this also refactors code to make more use of the
 existing `modifyGHCiState` operation.

 This is a preparatory refactoring for #10874

 Differential Revision: https://phabricator.haskell.org/D1582
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10874#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler