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💄🐞 Combinators for writing pretty type errors easily

License: Mozilla Public License 2.0

Haskell 100.00%

haskell type-level type-errors compile-time pretty hacktoberfest

type-errors-pretty's Introduction

type-errors-pretty

"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

Icons made by Freepik from www.flaticon.com is licensed by CC 3.0 BY.

type-errors-pretty's People

Contributors

Stargazers

Watchers

Forkers

jonathanlorimer brk felixonmars googleson78 winkduo hasktorch riugabachi collinarnett

type-errors-pretty's Issues

Support GHC-9.0

Test on some Windows CI

Upload 0.0.1.0 to Hackage?

Hi!

Is there something holding back the 0.0.1.0 version of this package from being uploaded to Hackage?

I am interested because I want to get polysemy to build with the latest stackage nightlies for ghc 8.8

Thanks in advance!

Too strict version requirements for ghc9.2.1

Tried building souffle-haskell with ghc9.2.1, which depends on this package.
Got this error:

Setup: Encountered missing or private dependencies:
base >=4.10.1.0 && <4.16

Looking at https://wiki.haskell.org/Base_package, ghc9.2.1 uses base 4.16.
Tried relaxing the constraints with doJailbreak in nix, but looks like things actually changed in base:

running tests
Running 1 test suites...
Test suite doctest: RUNNING...

src/Type/Errors/Pretty.hs:114:21: error:
    • Expected kind ‘k’, but ‘t :: Symbol’ has kind ‘Symbol’
    • In the first argument of ‘ToErrorMessage’, namely ‘(t :: Symbol)’
      In the type family declaration for ‘ToErrorMessage’
src/Type/Errors/Pretty.hs:82: failure in expression `:kind! "Integer values have type: " <> Int'
expected: "Integer values have type: " <> Int :: ErrorMessage
          = 'Text "Integer values have type: " ':<>: 'ShowType Int
 but got: 
          ^
          <interactive>:1:30: error:
              Not in scope: type constructor or class ‘<>’

src/Type/Errors/Pretty.hs:98: failure in expression `:kind! "Expecting value of type: " % "   " <> Integer'
expected: "Expecting value of type: " % "   " <> Integer :: ErrorMessage
          = 'Text "Expecting value of type: "
            ':$$: ('Text "   " ':<>: 'ShowType Integer)
 but got: 
          ^
          <interactive>:1:29: error:
              Not in scope: type constructor or class ‘%’
          
          <interactive>:1:37: error:
              Not in scope: type constructor or class ‘<>’

Examples: 2  Tried: 2  Errors: 0  Failures: 2

CommaSeparated '[ Int, String, Bool]

Will be displayed like this:

"Int, String, Bool"