idea: tool to suggest adding imports

Harendra Kumar harendra.kumar at
Fri Mar 18 19:12:05 UTC 2016

That's cool, I'd love to have that feature in my editor. Have you seen this:

The readme says:


Halberd is a tool to help you add missing imports to your Haskell source
files. With it, you can write your source without imports, call Halberd,
and just paste in the import lines.

Currently, it tries to automatically choose an import if there is a single
sensible option. If it can't, it will prompt you with a simple menu. After
running, it prints the imports, which you need to copy manually. Editor
integration is planned.


I have been thinking of exactly the same problem. That's how found this. I
have not tried it yet but this could be a starting point even if its not
working perfectly. In the best case you will have to just do the editor
integration part.


On 18 March 2016 at 23:57, John Williams <jrw at> wrote:

> I have an idea for a tool I'd like to implement, and I'm looking for
> advice on the best way to do it.
> Ideally, I want to write an Emacs extension where, if I'm editing Haskell
> code and I try to use a symbol that's not defined or imported, it will try
> to automatically add an appropriate import for the symbol. If instance, if
> I have "import Data.Maybe (isNothing)" in my module, and I try to call
> "isJust", the extension would automatically change the import to "import
> Data.Maybe (isJust, isNothing)".
> The Emacs part is easy, but the Haskell part has me kind of lost.
> Basically I want to figure out how to heuristically resolve a name, using
> an existing set of imports as hints and constraints. The main heuristic I'd
> like to implement is that, if some symbols are imported from a module M,
> consider importing additional symbols from M. A more advanced heuristic
> might suggest that if a symbol is exported from a module M in a visible
> package P, the symbol should be imported from M. Finally, if a symbol is
> exported by a module in the Haskell platform, I'd like to suggest adding
> the relevant package as a dependency in the .cabal and/or stack.yaml file,
> and adding an import for it in the .hs file.
> Here are some implementation options I'm considering:
> 1. Add a ghci command to implement my heuristics directly, since ghc
> already understands modules, packages and import statements.
> 2. Load a modified version of the source file into ghci where imports like
> "import M (...)" are replaced with "import M", and parse the error messages
> about ambiguous symbols.
> 3. Write a separate tool that reads Haskell imports and duplicates ghc and
> cabal's name resolution mechanisms.
> 4. Write a tool that reads Haskell imports and suggests imports from a
> list of commonly imported symbols, ignoring which packages are actually
> visible.
> Right now the options that look best to me are 2 and 4, because the don't
> require me to understand or duplicate big parts of ghc, but if modifying
> ghc isn't actually that hard, then maybe 1 is the way to go. Option 3 might
> be a good way to go if there are libraries I can use to do the hard work
> for me.
> Any thoughts?
> _______________________________________________
> Glasgow-haskell-users mailing list
> Glasgow-haskell-users at
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the Glasgow-haskell-users mailing list