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#### Maintainer's Corner

For package maintainers and hackage trustees

[back to package description]

Namely, it can do the following:

• for a module, compute its interface, i.e. the set of entities exported by the module, together with their original names.
• for each name in the module, figure out what it refers to — whether it's bound locally (say, by a where clause) or globally (and then give its origin).

## Installation

To install a released version:

1. Install Cabal and cabal-install from the git repository (the master branch)
2. cabal install haskell-names hs-gen-iface

If you're building a development version, then you might also need to install development versions of haskell-src-exts, haskell-packages, and hse-cpp.

## Module interfaces

hs-gen-iface is a «compiler» that generates interfaces for Haskell modules.

An interface is a JSON file that lists all entities (types, classes, functions etc.) exported by every module. For example, here are a couple of entries from Prelude.names:

[
{
"name": "map",
"entity": "value",
"module": "GHC.Base"
},
{
"name": "IO",
"entity": "newtype",
"module": "GHC.Types"
},
...
]


As you see, each entity is annotated with the module where it was originally defined. Additionally, class methods, field selectors, and data constructors are annotated with the class or type they belong to.

### Generating interfaces

Thanks to haskell-packages, hs-gen-iface is fully integrated with Cabal. To produce and install interface files, pass --haskell-suite -w hs-gen-iface flags to cabal install, for instance

cabal install --haskell-suite -w hs-gen-iface mtl


This assumes that the hs-gen-iface executable is in your PATH. You can specify the full path to hs-gen-iface after -w, too.

#### Core packages

haskell-names comes with the global package database populated with some core packages:

% hs-gen-iface pkg list --global
array-0.4.0.2
base-4.7.0.0
integer-simple-0.1.1.0
ghc-prim-0.3.1.0


#### Compiling core packages by hand

Suppose you need to compile any of the core packages by hand — for example, to get a different version than the one bundled with haskell-names.

Core packages, such as ghc-prim, integer-simple, array, and base, are highly GHC-specific and need to be tweaked a bit before they can be processed by haskell-names. Get our modified versions:

Note that Cabal's new dependency solver won't let you install ghc-prim or base easily. There are two ways to work around this:

1. Use the old solver:

 cabal install --haskell-suite -w hs-gen-iface --solver=topdown

2. Invoke all the steps manually:

 cabal configure --haskell-suite -w hs-gen-iface
cabal build
cabal install --only


### Using interfaces

You can parse interface files directly, but a better idea is to use Distribution.HaskellSuite.Packages API (from haskell-packages), combined with the package database NamesDB defined in Language.Haskell.Modules.Interfaces.

## Name resolution

The annotateModule function annotates the module with scoping information.

Its essence is described in the article Open your name resolution.

### Example

Let's say you have a module and you want to find out whether it uses Prelude.head.

module Main where

import qualified Language.Haskell.Exts as UnAnn (Name(Ident))
import Distribution.Simple.Compiler

import Data.Maybe
import Data.List
import Data.Proxy
import qualified Data.Foldable as Foldable
import Text.Printf
import Control.Applicative

main :: IO ()
main = do

-- read the program's source from stdin
source <- getContents

let
-- parse the program (using haskell-src-exts)
ast = fromParseResult $parseModuleWithMode defaultParseMode {parseFilename="stdin"} source -- get all installed packages (user and global) pkgs <- (++) <$>
getInstalledPackages (Proxy :: Proxy NamesDB) UserPackageDB <*>
getInstalledPackages (Proxy :: Proxy NamesDB) GlobalPackageDB

forM_ headUsages $\loc -> printf "Prelude.head is used at %s\n" (prettyPrint$ srcInfoSpan loc)

when (null headUsages) $printf "Congratulations! Your code doesn't use Prelude.head\n" -- | The findHeads function finds all occurrences of the head symbol in -- a given AST of a Haskell module. It needs access to stored name information -- and therefore runs in ModuleT. findHeads :: Module SrcSpanInfo -> ModuleT [Symbol] IO [SrcSpanInfo] findHeads ast = do -- First we get all symbols exported from Prelude with getModuleInfo. symbols <- fromMaybe (error "Prelude not found") <$>
getModuleInfo "Prelude"

-- Then we filter those for the one with name "head".
let
symbol <- symbols
guard (symbolName symbol == UnAnn.Ident "head")
return symbol))

-- We annotate the given ast.
annotatedAst <-
annotateModule
[]          -- set of extensions
ast

-- We get a list of all annotations from the annotated module.
let
annotations = Foldable.toList annotatedAst

-- A GlobalSymbol annotation means that the annotated name refers to a
-- global symbol. It also contains the qualified name that corresponds
-- to how it is referenced but that is not needed here.
Scoped (GlobalSymbol globalSymbol _) location <- annotations
return location)

-- And finally we return all found usages.



#### Example invocation

% ./find-heads
^D
Prelude.head is used at stdin: (1:7) - (1:11)

import Data.Text

^D


### API documentation

The two modules you need are:

Other modules are more experimental, less documented, and you probably don't need them anyway.

### Known issues

See the list of all issues.

• Because a non-trivial amount of packages are not designed to work with anything except GHC, hs-gen-iface currently pretends to be GHC. This is of course not acceptable — contributions here are welcome. (#32)
• haskell-names doesn't perform validation yet. If a module is not valid Haskell, then the behaviour is undefined. See the issues marked as validation.
• Symbol fixities are not recorded (#1)
• Type variables are not resolved (#2)
• Arrows are not fully supported (#8)

## Maintainers

Philipp Schuster is the primary maintainer.

Adam Bergmark is the backup maintainer. Please get in touch with him if the primary maintainer cannot be reached.