[GHC] #10920: ghci can't load local Prelude module

[GHC]

#10920: ghci can't load local Prelude module
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        Reporter:  Yuras             |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  7.10.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by gelisam):

 osa1, I am not that person, but here is an explanation. If you have a file
 called `./Foo.hs` and you try to import it, `ghci` tells you that it
 doesn't know about that file, because you haven't loaded it yet:

 {{{
 $ ghci
 GHCi, version 7.10.2: http://www.haskell.org/ghc/  :? for help
 Prelude> import Data.List
 <no location info>:
     Could not find module ‘Foo’
     It is not a module in the current program, or in any known package.
 }}}

 The solution is to run `:load Foo.hs` before `import Foo`.

 If you have a file called `./Data/List.hs`, this now conflicts with the
 `Data.List` from `base`, so you get a different message clarifying which
 module is not loaded:

 {{{
 $ ghci
 GHCi, version 7.10.2: http://www.haskell.org/ghc/  :? for help
 Prelude> import Data.List
 <interactive>:1:1:
     attempting to use module ‘Data.List’ (./Data/List.hs) which is not
 loaded
 }}}

 The solution is to run `:load Data/List.hs` before `import Data.List`.

 Now without `-XNoImplicitPrelude`, `ghci` begins by running `import
 Prelude`, which normally succeeds by loading the Prelude from `base`, but
 in this case, since there is a `./Prelude.hs` file, `ghci` tells you that
 it can't use that file because it isn't loaded yet.

 Since the user didn't explicitly type `import Prelude`, the error message
 is confusing, so maybe there should be some special logic to give a
 different message in that case or even to implicitly `:load ./Prelude.hs`.
 Note, however, that there are other modules than Prelude which can trigger
 this error message when particular files are present and the user hasn't
 explicitly typed an import statement. If your `.ghci` has an `import
 Data.List` intended to import the `Data.List` from `base`, it will usually
 work, until you have a local file called `./Data/List.hs` in which case
 `ghci` will complain on startup with this same message that it can't use
 `./Data/List.hs` because it is not loaded.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10920#comment:2>
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