Binding type variables is not allowed in pattern bindings [GHC-48361]

Patterns can bind constructor arguments to variables, but they are not able to bind type arguments to type variables.

Examples

Binding type variables is not allowed in pattern bindings

Error Message

Error.hs:4:1: error: [GHC-48361]
    • Binding type variables is not allowed in pattern bindings
    • In the pattern: Just @a x
      In a pattern binding: Just @a x = Just (5 :: Integer)
  |
4 | Just @a x = Just (5 :: Integer)
  | ^^^^^^^^^

Error.hs

Before

module Main where

x :: Integer
Just @a x = Just (5 :: Integer)

After

module Main where

x :: Integer
Just x = Just (5 :: Integer)