Pipeline Operator (Stage 1)

[hzoo]

Champion: @littledan
Spec Repo: https://github.com/tc39/proposal-pipeline-operator
First presented at Sept 2017 meeting: https://github.com/tc39/agendas/blob/master/2017/09.md
Slides: https://docs.google.com/presentation/d/1qiWFzi5dkjuUVGcFXwypuQbEbZk-BV7unX0bYurcQsA/edit#slide=id.p
Related proposal: Partial Application https://github.com/rbuckton/proposal-partial-application by @rbuckton
Related proposal: Function Bind Operator https://github.com/tc39/proposal-bind-operator

Basic Example

Input

let result = "hello"
  |> doubleSay
  |> capitalize
  |> exclaim;
result //=> "Hello, hello!"

Output

let result = exclaim(capitalize(doubleSay("hello")));
result //=> "Hello, hello!"

Initial Implementation (would need updating to v7)

• Initial Spec PR by @littledan Add a specification tc39/proposal-pipeline-operator#51

Old/Alternative Implementations

• Old PR to Babel: New plugin for pipeline operator proposal babel#3159
• https://github.com/SuperPaintman/babel-plugin-transform-pipeline
• << and >>: https://github.com/michaelmitchell/babel-plugin-pipe-composition

cc @gilbert, @SuperPaintman

Implementation

• Parser PR: Pipeline Operator proposal babylon#742
• Transform PR: Pipeline operator babel#6335
• Feedback around relating Pipeline Operator, Function Bind, Partial Application

[nicolo-ribaudo]

There is also another Babylon implementation (https://github.com/airdwing/babylon), which could be already mergeable because the fork was updated one month ago.

[hzoo]

didn't know it was that simple ha - needs hasPlugin, tests, readme, etc though

[nicolo-ribaudo]

Oh right 😅

[hzoo]

Merged the parser PR

[hzoo]

Transform PR: babel/babel#6335, test at https://babeljs.io/repl/build/5099/

[hzoo]

Linking to Dan's syntax concern (not specced) tc39/proposal-pipeline-operator#60

[hzoo]

Some syntax used in the spec repo examples that doesn't parse currently: are these supposed to be?

class Comment extends Model |> Editable |> Sharable {}

[ljharb]

I would expect that to parse as long as Model |> Editable |> Sharable parses, since the RHS of extends is an expression.

[littledan]

@hzoo You are right, the explained does not match the spec. Sorry for this state of things. I hope to address it soon.