https://github.com/lue-bird/elm-review-single-use-type-vars-end-with-underscore

enforce that type variables only used once end with -_
https://github.com/lue-bird/elm-review-single-use-type-vars-end-with-underscore

elm elm-review type-variable

Last synced: 4 months ago
JSON representation

enforce that type variables only used once end with -_

• Host: GitHub
• URL: https://github.com/lue-bird/elm-review-single-use-type-vars-end-with-underscore
• Owner: lue-bird
• License: mit
• Created: 2021-07-04T05:13:28.000Z (about 4 years ago)
• Default Branch: master
• Last Pushed: 2025-02-27T22:13:55.000Z (5 months ago)
• Last Synced: 2025-03-27T08:47:59.580Z (4 months ago)
• Topics: elm, elm-review, type-variable
• Language: Elm
• Homepage: https://package.elm-lang.org/packages/lue-bird/elm-review-single-use-type-vars-end-with-underscore/latest/
• Size: 146 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Changelog: changes.md
  • Contributing: contributing.md
  • License: LICENSE

Awesome Lists containing this project

README

        
# [elm-review-single-use-type-vars-end-with-underscore](https://dark.elm.dmy.fr/packages/lue-bird/elm-review-single-use-type-vars-end-with-underscore/latest/)

The [`elm-review`](https://dark.elm.dmy.fr/packages/jfmengels/elm-review/latest/) rule

🔧[`OnlyAllSingleUseTypeVarsEndWith_`](OnlyAllSingleUseTypeVarsEndWith_)

enforces that type variables which are only used once

in annotations of module scope declaration

are marked with the suffix -\_ and other type variables are not.

## why would you want this?

You can use -\_ at the end of a type variable to indicate that it is used only in this one place.

Some types have a lot of type variables, most of them only used once.

If you see a -\_, you know not to focus on these

  - -\_ in the result: can be inferred as anything

  - -\_ in an argument: anything allowed

  

The review rule makes sure that this type variable isn't used anywhere else

so that 2 type variables can't accidentally be the same.

```elm

httpRequestSend :

    { url : String

    , method : String

    , onResponse : Bytes -> msg

    , headers :

          List

              { name : String

              , value : String

              }

    , body : Maybe Bytes

    }

    -> Task error_ msg

```

We can see at a glance that `error_` isn't related to an argument,

it's free to take on any type whereas `msg` is something an argument has to provide.

Likewise, if we see `-_` in an argument, we also know it's not used in any other part of the type.

```elm

nodeCount :

    lockingTag

    -> TaggedTree label_ lockingTag

    -> Int

```

## configure

```elm

module ReviewConfig exposing (config)

import OnlyAllSingleUseTypeVarsEndWith_

import Review.Rule

config : List Review.Rule.Rule

config =

    [ OnlyAllSingleUseTypeVarsEndWith_.rule

    ]

```

## why you might not want this

  - The conventional way of naming type variables is used consistently 

    in pretty much all existing elm code and is already familiar to elm folks

  - you already use -/_ for separate reasons in some type variables

  - since `let` declaration annotations may need to refer to types that are single-use in the module-scope declaration annotation, this review rule does not consider `let` type variables at all which might be confusing

Ultimately, the solution to fix all three

would be an editor extension that de-emphasizes (less contrast, ...) single-use type variables.