Haskell : unload module in WinGHCi

Question

I loaded two modules (NecessaryModule1.hs and NecessaryModule2.hs as outlinked in Haskell : loading ALL files in current directory path). Now I want to unload NecessaryModule2.hs. I found an 'unload' function in System.Plugins.Load however but it did not work in WinGHCi. The error message I got was : ``` >unload NecessaryModule2 :1:1: Not in scope: `unload' :1:8: Not in scope: data constructor `NecessaryModule2' ``` I tried ``` import System.Plugins.Load ``` but that did not work. Is there a way to unload modules in the manner described above? --------------------------------------------------------------------------------------- [RESPONSE TO Riccardo] Hi Riccardo, I tried your suggestion but I could not get it to work in WinGHCi. I had a file NecessaryModule1.hs as follows : ``` module NecessaryModule1 where addNumber1 :: Int -> Int -> Int addNumber1 a b = a + b ``` I went to the location of the file via the ':cd' command, and then did : ``` > :module +Neces…

Accepted Answer

Installed modules

You have to use ghci's commands in order to load (`:module +My.Module`) and unload (`:module -My.Module`) installed modules. You can also use `:m` instead of `:module` in order to write less, like this:

```
Prelude> :m +Data.List
Prelude Data.List> sort [3,1,2]
[1,2,3]
Prelude Data.List> :m -Data.List
Prelude> sort [3,1,2]

<interactive>:1:1: Not in scope: `sort'
```

Remember that the ghci prompt always reminds you the module currently imported: you can have a look at that in order to know what to unload with `:m -Module.To.Unload`.

Specific files

If the module you're trying to load isn't installed in the system (e.g. you wrote the source and simply saved the file somewhere), you need to use a different command, `:load filename.hs`. A quicker way is to pass the path to the file directly as a command-line argument to `ghci`, e.g `ghci filename.hs`. If you run `winghci` and you associated it to the `.hs` extension, simply double-click the file.

In both cases you will get a ghci prompt with the specified module correctly loaded AND imported in scope (provided you don't have get compilation errors instead). As before, you can now use `:m [+/-] My.Module` to load and unload modules, but please note that this is different from `:load` because `:module` assumes you already `:load`ed what you're trying to get in/out of scope.

E.g., if you have `test.hs`

```
module MyModule where
import Data.List

f x = sort x
```

you may load it by double-clicking it (on windows with winghci), by typing `ghci test.hs` in a console, or by loading `ghci` and typing `:load test.hs` (beware of relative/absolute paths).

Another useful ghci command is `:reload`, which will recompile the module you loaded before. Use it when you change the source file and you want to quickly update the module loaded in ghci.

```
Prelude> :load test.hs
[1 of 1] Compiling MyModule         ( test.hs, interpreted )
Ok, modules loaded: MyModule.
*MyModule> let xs = [1,2,3] in sort xs == f xs
True
*MyModule> :reload
Ok, modules loaded: MyModule.
```

`:help` will give you a complete list of all available commands.

Haskell : unload module in WinGHCi

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