[Haskell-cafe] How to determine the right path to haddock html documentation?

[Roman Cheplyaka]

String is defined in GHC.Base, but GHC.Base is an internal (not exposed)
module of the base package; that's why there's no documentation for it.

Instead of asking where the thing is defined, you should be asking where
it's exported from. In this case, String is re-exported from Prelude.

Roman

* Carlo Hamalainen <carlo at carlo-hamalainen.net> [2013-12-13 22:50:40+0100]
> Hi,
> 
> I'm writing a patch for ghcmod-vim so that a user can look up the
> haddock html documentation for a symbol. My code makes three system
> calls, e.g. to look up "Just" it does:
> 
>     $ ghc-mod info foo.hs Foo Just
>     data Maybe a = ... | Just a     -- Defined in `Data.Maybe'
> 
>     $ ghc-pkg find-module Data.Maybe --simple-output
>     haskell2010-1.1.1.0 base-4.6.0.1
> 
>     $ ghc-pkg field base-4.6.0.1 haddock-html
>     haddock-html:
> /home/carlo/opt/ghc-7.6.3_build/share/doc/ghc/html/libraries/base-4.6.0.1
> 
> Then "Data.Maybe" is changed to Data-Maybe.html" and appended to the
> haddock-html value. But this procedure doesn't work in general, for
> example when looking up String:
> 
>     $ ghc-mod info foo.hs Foo String
>     type String = [Char]     -- Defined in `GHC.Base'
> 
>     $ ghc-pkg find-module GHC.Base
>     /home/carlo/opt/ghc-7.6.3_build/lib/ghc-7.6.3/package.conf.d
>        base-4.6.0.1
>     /home/carlo/.ghc/x86_64-linux-7.6.3/package.conf.d
> 
>     $ ghc-pkg field base-4.6.0.1 haddock-html
>     haddock-html:
> /home/carlo/opt/ghc-7.6.3_build/share/doc/ghc/html/libraries/base-4.6.0.1
> 
>     $ ls
> /home/carlo/opt/ghc-7.6.3_build/share/doc/ghc/html/libraries/base-4.6.0.1/GHC-Base.html
>     ls: cannot access
> /home/carlo/opt/ghc-7.6.3_build/share/doc/ghc/html/libraries/base-4.6.0.1/GHC-Base.html:
> No such file or directory
> 
> because the html is in the src subdirectory:
> 
>     $ ls
> /home/carlo/opt/ghc-7.6.3_build/share/doc/ghc/html/libraries/base-4.6.0.1/src/GHC-Base.html
>    
> /home/carlo/opt/ghc-7.6.3_build/share/doc/ghc/html/libraries/base-4.6.0.1/src/GHC-Base.html
> 
> But this isn't even the right place to go, one should look at the
> Prelude file
> 
> http://hackage.haskell.org/package/base-4.6.0.1/docs/Prelude.html#t:String
> 
> which is what Hoogle suggests. How does Hoogle get it right?
> 
> It looks like haskell-mode for emacs runs into a similar problem:
> 
> https://github.com/haskell/haskell-mode/blob/master/inf-haskell.el#L734-L740
> 
> -------------------------------
>   (defvar inferior-haskell-ghc-internal-ident-alist
>     ;; FIXME: Fill this table, ideally semi-automatically.
>     '(("GHC.Base.return" . "Control.Monad.return")
>       ("GHC.List" . "Data.List")))
> 
>   (defun inferior-haskell-map-internal-ghc-ident (ident)
>     "Try to translate some internal GHC identifier to its alter ego in
> haskell docs."
> -------------------------------
> 
> Thanks,
> 
> -- 
> Carlo Hamalainen
> http://carlo-hamalainen.net
> 

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