[Haskell-cafe] Coding conventions for Haskell?

Christopher Done chrisdone at googlemail.com
Thu Sep 30 19:24:23 EDT 2010

On 30 September 2010 21:02, Bas van Dijk <v.dijk.bas at gmail.com> wrote:
> Note that, although I don't use it myself, the GHC flag:
> -ddump-minimal-imports can help you with this style:
> http://www.haskell.org/ghc/docs/6.12.2/html/users_guide/separate-compilation.html#hi-options

Indeed, after discovering this I thought about writing a little Emacs
Lisp to have a keybinding for updating my imports using
-ddump-minimal-imports, so that I can write without explicit import
but then make it explicit when I'm done automatically. I forgot about
it so thanks for reminding me.

Ideally I would also write some functions that make automatic import
of a symbol easier. There are 4 problems with writing Haskell and
managing imports, as I see it, right now (I'll make up some names to
encapsulate these ideas):

1. Pretty printing: The order and spacing of imports.
2. Explicitness: The explicit naming of imported symbols, or qualification.
3. Discovery: Calculating where the symbol I'm using right now should
be imported from, and then adding that import either automatically or
4. Pruning: Removing unnecessary imports, and merging imports which
are the same.

I made some functions to make it easier to jump back and forth to
imports, but now I don't really want to manually write out an import
statement again. I'd prefer to have Emacs present me with options,
i.e., these are the modules that export that type/symbol/class, pick
one (with ido/fuzzy completion) and then it adds the import line at
the correct place with the desired spacing and with the necessary

You also sometimes refactor part of a module to another module, and
then you need to copy over all the necessary imports. I tend to copy
all my imports over and then remove the ones GHCi tells me aren't
necessary. So, one solution to make this automatic copy over all the
imports from the current module and then prune.

Perhaps I will attempt some of this on the weekend, as it's the
biggest pain I have right now writing Haskell code. I spend a lot of
time just maintaining my imports.

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