Grammar rules in proposed spec text seem incomplete

[sethbrenith]

Based on the description in README.md, it seems that the pipeline operator is intended to be left-associative: a |> b |> c is equivalent to (a |> b) |> c. The proposed spec text defines the following production:

    PipeExpression[In, Yield, Await] :
      ShortCircuitExpression[?In, ?Yield, ?Await] |> PipeBody[?In, ?Yield, ?Await]

However, the proposed text does not include any rules for how ShortCircuitExpression can be a PipeExpression, which I assume would be necessary for parsing a |> b |> c.

Furthermore, in order for the grammar to be unambiguous, the right side of the PipeExpression production should be something which can't be a PipeExpression. If we assume ShortCircuitExpression can be a PipeExpression, then PipeBody can also be a PipeExpression with the current production rules, which causes ambiguity. I expect the production to be of the form:

    PipeExpression :
      SomethingWhichCanBeAPipeExpression |> SomethingWhichCannotBeAPipeExpression

I expect it will be somewhat difficult to define unambiguous grammar rules for a new left-associative operator which is at the same precedence level as a bunch of existing right-associative operators; this may be indicative of a fundamental problem with the currently proposed precedence level.

[tabatkins]

It actually doesn't matter whether the pipe is left- or right-associative; either associativity gives identical evaluation results.

I'm not sure if that affects your point, just saying.

[sethbrenith]

Oh, excellent point! If it works as right-associative, then I'm no longer concerned about the proposed operator precedence. Thanks.

In that case, I think we just need the proposed spec to include a modification to the expansion rules for AssignmentExpression to indicate that it can be a PipeExpression.