haskell / haskell/error-messages

Perhaps you meant a :: Maybe Int

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#17 6 comments 2 reactions 0 assignees View on GitHub
status:Composing error message tool:GHC type:error-message
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Description

Given this code:

```haskell
a :: Just Int
a = Just 5
```

GHC errors with:

```haskell
Not in scope: type constructor or class 'Just'A data constructor of that name is in scope; did you mean DataKinds?
```

A better error message would be:

```haskell
Perhaps you meant a :: Maybe Int?
Not in scope: type constructor or class 'Just'
A data constructor of that name is in scope; did you mean DataKinds?
```

Suggested on reddit: https://www.reddit.com/r/haskell/comments/kgvdon/improving_haskell_ghc_error_messages/gghjajf/?utm_source=reddit&utm_medium=web2x&context=3

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