please allow value definitions before the first generator in a for comprehension

[scabug]

I would like to be able to write this:

for{x = foo(bar); y <- x} ...

the language spec (6.19) says "An enumerator sequence always starts with
a generator", but why? From time to time I would find it convenient to put
a value definition first. I realize that in the above code I only use x once,
but I've hit this in real code where I want to use x more than once.

(Perhaps "if" should be allowed too?)

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-907?orig=1
Reporter: @SethTisue

[scabug]

@paulp said:
While I agree with the sentiment on an aesthetic level, the overhead of such a change (in implementation and testing as well as updating the language spec, documentation, and etc.) has been deemed too high to justify it, as the known use cases are marginal. So I'm closing this as wontfix, but please update the ticket if you come across a compelling motivation.

[scabug]

Samuel Halliday (fommil) said:
Is there any reason this couldn't be implemented as a parser rewrite to move the value definition out of the for?

e.g. rewrite Seth's original example as

val x = foo(bar)
for {y <- x}

[fommil]

I'd really like to see this ticket reopened.

[jvican]

I'm not sure this workaround:

val x = foo(bar)
for {y <- x}

is worth it. I think we have already enough desugarings in parser. Putting more would force all the Scala tooling to catch up and I don't think it's a neat solution overall, but rather a hack.

[fommil]

for FP code this is definitely worth it. This comes up all the time when for is your main language structure for sequential code.

[fommil]

btw, apparently we should be discussing at https://contributors.scala-lang.org/t/ressurrect-assignment-as-first-line-of-for/808