Unsupported extension [GHC-46537]

This error is reported when GHC fails to recognize the name of a language extension, provided via {-# LANGUAGE ... #-} pragma at the top of a .hs file.

There are two likely causes:

You’ve made a typo, in which case GHC will likely also suggest the correct extension name to use.
You’re using older version of GHC that doesn’t yet support the extension. Here’s a couple of things you can try in order to troubleshoot:
- Find out which version of GHC you’re using:
```
ghc --version
```
- List all the supported extensions that this version of GHC supports. Does the list contain your desired extension?
```
ghc --supported-extensions
```
- Search for the extension name in the latest version of the GHC User’s Guide. Most extensions have a since annotation which tells you in which version of GHC the extension was introduced.

Examples

Unsupported extension

Error Message

Main.hs:1:14: error: [GHC-46537]
    Unsupported extension: ExistientialQuantification
    Suggested fix:
      Perhaps you meant ‘ExistentialQuantification’ or ‘NoExistentialQuantification’
  |
1 | {-# LANGUAGE ExistientialQuantification #-}
  |              ^^^^^^^^^^^^^^^^^^^^^^^^^^

UnsupportedExtension.hs

Before

{-# LANGUAGE ExistientialQuantification #-}
-- typo here      ^                
module UnsupportedExtension where

After

{-# LANGUAGE ExistentialQuantification #-}

module UnsupportedExtension where