kowainik/type-errors-pretty

---

kowainik/type-errors-pretty.json

{
  "createdAt": "2019-07-13T10:15:56Z",
  "defaultBranch": "main",
  "description": "💄🐞 Combinators for writing pretty type errors easily",
  "fullName": "kowainik/type-errors-pretty",
  "homepage": "",
  "language": "Haskell",
  "name": "type-errors-pretty",
  "pushedAt": "2022-03-07T18:30:31Z",
  "stargazersCount": 56,
  "topics": [
    "compile-time",
    "hacktoberfest",
    "haskell",
    "pretty",
    "type-errors",
    "type-level"
  ],
  "updatedAt": "2025-04-16T18:54:31Z",
  "url": "https://github.com/kowainik/type-errors-pretty"
}

type-errors-pretty

[]!(LICENSE)

“It is important that we forgive ourselves for making mistakes. We need to learn from our errors and move on.”

― Steve Maraboli, Life, the Truth, and Being Free

Combinators for writing pretty type errors easily. The word pretty here doesn’t mean that the resulting type errors will be pretty (though, I believe they will be awesome), but the way the type errors are defined in your code is pretty.

If you’re interested in motivation behind using type errors at first place, you can read the following blog post:

• A story told by Type Errors

The type-errors-pretty library allows you to write the text of custom compile-time error messages with less effort in the following way:

import Type.Errors.Pretty (type (<>), type (%))


type MessageText (e1 :: k) (e2 :: k) (es :: [k])
    = "You require the following two effects from your computation:"
    % ""
    % "    '" <> e1 <> "' and '" <> e2 <> "'"
    % ""
    % "However, your monad is capable of performing only the following effects:"
    % ""
    % "    " <> es

Acknowledgement

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