F# pipeline operator

[goodmind]

Discussion: #5443

• await parsing
• arrow body parsing
• .flowconfig option

[goodmind]

[goodmind]

I ended up implementing typechecking as well 😀
But I have no idea how to implement arrow functions without parens

[goodmind]

Babel PR babel/babel#9450 for reference

[goodmind]

Well, there's already was function body parsing in assignment_cover, so I just copy-pasted it

[goodmind]

I don't think it's possible to implement all three proposals in Flow, because there isn't such thing as parser plugins.
Flow just parses everything and then errors on wrong things with PseudoParseError

[goodmind]

@mAAdhaTTah What you think? Is this still too early?

[mAAdhaTTah]

Probably. I don't know the Flow team's policy around this sort of thing. I know TS won't implement anything until stage 3, especially after the pain they've had with decorators.

I'll point out that the committee isn't necessarily sold on the operator at all and there is a significant contingent who prefer the bind operator. Not only are we risking implementing the wrong version of the operator, we're risking the syntax not advancing and needing to rip it out.

[goodmind]

Well, Flow supports nullish coalescing, and optional chaining under flag, but they're still stage 2, but doesn't support other proposals
Also Flow even implements enums without proposal (but it probably would be released), so it is technically stage -1 #7837

[goodmind]

@mAAdhaTTah I thought bind operator was dropped in 2015 and always was stage 0?

[mAAdhaTTah]

AFAIK, Bind is still Stage 1, but it's stalled out. However, we have gotten suggestions, including from committee members, about bind: tc39/proposal-pipeline-operator#110 and tc39/proposal-pipeline-operator#107 so I'm still viewing it as a competing proposal.

[SamChou19815]

Closing since the PR has too many merge conflicts, and we do not plan to implement proposals before stage 3