In VS Code how to make symbol renaming work in simple modules?

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1

When I have a simple module and i try to rename a symbol in VS Code I get from the editor the error

Screen Shot 2023-03-27 at 6.39.42 am

With “simple module” I mean jere something like this code:

-- File Cnt.hs
module Cnt where

mostFrequentChar' :: String -> Char -> Int -> (Char, Int)
mostFrequentChar' [] maxChar maxFreq = (maxChar, maxFreq)
mostFrequentChar' (c:cs) maxChar maxFreq =
    let freq = count c (c:cs)
    in if freq > maxFreq
        then mostFrequentChar' cs c freq
        else mostFrequentChar' cs maxChar maxFreq
    where count x xs = length $ filter (== x) xs

No exports (what ever this is). I just want to rename mostFrequentChar' to mostFrequentChar

But I can’t. Why’s that? Can I tweak VS Code’s HLS settings, so that the renaming works?

Many thanks in advance for any help.

2

Here’s an example of an explicit export list for your module:

module Cnt (mostFrequentChar') where

It makes explicit that the function mostFrequentChar' is exported from the module Cnt.

I don’t know why HLS requires an explicit export list, but it seems like the renaming will succeed if you add it.

3

Well, if your module doesn’t have an explicit export list – as @jaror shows – then in effect it exports every top-level name declared in the module. (You haven’t named your module Main, so Haskell expects this isn’t ‘the’ ‘commanding’ module.)

Yeah, I don’t know either. Seems VS Code is being over-bureaucratic. If your module is being imported somewhere else, you’ll need to change all the usage sites to the new name – although the imports might or might not name your id explicitly.

Perhaps for VS Code in general/not specific to Haskell, you can rename across a whole application/multiple modules as one operation? And VS Code will go off cross-referencing by export/import names(?)

4

Thanks @AntC2 and @jaror.

In my case I have no big project, just this module as a stand-alone file which load into ghci. – It feels a bit over the top just in order to satisfy the editor to add some export clauses… Would be nice if VS Code could deal with that. (For the moment I use plain find/replace to get around this limitation.)

5

I have also found myself frustrated with this.

6

It is really annoying when you want to rename a variable (not even a top level function) and you need to add an explicit export list

7

Hm yeah. Is this just a bug?

Also, what happens if you just use an empty export list?

module Foo () where
8

It works :confused: . But if you do so, you are exporting nothing from the module isn’t it?

9

Yeah, this is probably the easiest workaround for the original problem, but it seems likely that this is just a bug…

10

What happens if you use a module re-export?

module Foo (module Foo) where
11

When I last checked, HLS explicitly disallows renaming exported bindings. Maybe the error is due to this problem, which means there would be no satisfactory workaround…

12

Ah, that makes sense!

13

In which case the error message should probably say something like “Cannot rename an exported binding”.

14

This situation is really inconvenient!

For now I use just VS Code’s language-independent search-and-replace commands, but they are pretty cumbersome and fragile in comparison with a proper Replace Symbol command…

15

Coming back here again: I went off to the HLS issues on GitHub and received there fantastic help from @July541:

When you enable (experimental) crossModule renaming, than you can rename symbols local to a module perfectly without any export list! For how to do it in VS Code, see this comment in the issue.

16

Finding this was a game-changer for me, thank you so much!