On 14/12/13 15:02, Roman Cheplyaka wrote: 
haskell-names can also do this (it's used in halberd to solve a similar
task: https://github.com/haskell-suite/halberd)

This is quite useful, thanks.

For the benefit of the list archive, here is what I have worked out so far.

I took the example from http://www.haskell.org/haskellwiki/GHC/As_a_library which uses getNamesInScope (I thought that this was promising). But it returned an empty list for the list of names (variable 'n'). I found out that you have to set the context before the call to getNamesInScope, like so:

https://github.com/carlohamalainen/playground/blob/master/haskell/ghc_symbol_lookup/A.hs


        target <- guessTarget targetFile Nothing
        setTargets [target]
        load LoadAllTargets

        -- http://stackoverflow.com/questions/11571520/reify-a-module-into-a-record
        setContext [IIDecl (simpleImportDecl (mkModuleName "B"))]

        modSum <- getModSummary $ mkModuleName "B"

For example on this file,

-- B.hs
module B where

import Data.Maybe

f :: a -> Maybe a
f x = Just x

s = "boo" :: String

main = print "Hello, World!"

we can get the list of names and also the imports:

$ runhaskell A.hs
([B.main, B.f, B.s],
 [main, B.main, f, B.f, s, B.s],
 [],
 [import (implicit) Prelude, import Data.Maybe])

I'm not sure why, but the "source imports" is an empty list, while the "textual imports" gives the implicit Prelude and Data.Maybe. Also the names are the program names like f, s, and main, and don't include things like String, Int, Just, and so on.

Independently of that, I tweaked an example from the haskell-names docs and this lets me see where String comes from, e.g.

https://github.com/carlohamalainen/playground/blob/master/haskell/ghc_symbol_lookup/haskell_names_example.hs


$ cat B.hs | runhaskell haskell_names_example.hs

Relevant bits:

"Prelude"

SymType {st_origName = OrigName { origPackage = Just (PackageIdentifier { pkgName = PackageName "base"
                                                                        , pkgVersion = Version {versionBranch = [4,7,0,0]
                                                                        , versionTags = []}})
                                 , origGName = GName { gModule = "GHC.Base"
                                                     , gName = "String"}}
        , st_fixity = Nothing}


"Data.Maybe"

SymConstructor {sv_origName = OrigName { origPackage = Just (PackageIdentifier { pkgName = PackageName "base"
                                                                              , pkgVersion = Version {versionBranch = [4,7,0,0]
                                                                              , versionTags = []}})
                                       , origGName = GName { gModule = "Data.Maybe"
                                                           , gName = "Just"}}
                                                           , sv_fixity = Nothing
                                                           , sv_typeName = OrigName { origPackage = Just (PackageIdentifier { pkgName = PackageName "base"
                                                                                                                            , pkgVersion = Version { versionBranch = [4,7,0,0]
                                                                                                                                                   , versionTags = []}})
                                                                                    , origGName = GName { gModule = "Data.Maybe"
                                                                                                        , gName = "Maybe"}}}



This is pretty much what I'm after. The first block shows us that String is exported from the Prelude, even though it's defined in GHC.Base. The second block says that the constructor Just is actually exported from Data.Maybe.

So these ought to able to be stitched together: work through the textual imports one at a time until a symbol appears and then find the haddock_html field for the package using ghc-pkg.

-- 
Carlo Hamalainen
http://carlo-hamalainen.net