emit statement not working as expected in mlr 6.0

[vapniks]

This works fine with miller 5.3.0:

mlr -n put 'end {@in={"a":1}; emit @in["a"]}'

but gives the following error with the latest miller 6.0.0-rc (0b71298):

mlr: cannot parse DSL expression.
Parse error on token "[" at line 1 columnn 27.
Please check for missing semicolon.
Expected one of:
  ; } ,

[johnkerl]

Hi @vapniks --

Bit of a story here.

emit goes way back early on in Miller, even before there were control structures like for loops. I put (in hindsight) too much syntactic complexity into emit, which wouldn't have been necessary if there had been other things like for loops.

The grammar is more complex in Miller 6, and I'm using a different parser-generator, without shift-reduce-conflict hacks in my use of it (I hope I'm not over-jargoning). At this point, allowing emit of indexed things is no longer possible in the grammar without either introducing shift-reduce conflicts (i.e. a parser-generator cannot be built for the grammar), or perhaps introducing new emit syntax.

What I think is the best (or perhaps least-bad) course is to more clearly document at
https://miller.readthedocs.io/en/latest/reference-dsl-output-statements/#emit1-and-emitemitpemitf
that we can't emit indexed oosvars now, and to document a suggested replacement of the form

$ mlr -n put 'end {@in={"a":1}; @ina = @in["a"]; emit @ina}'
ina=1

at https://miller.readthedocs.io/en/latest/new-in-miller-6/.

What do you think?

[johnkerl]

@vapniks updated advice:

$ mlr5 -n put 'end {@in={"a":1}; emit @in["a"]}'
in=1

$ mlr -n put 'end {@in={"a":1}; emit1 {"in":@in["a"]}}'
in=1

[johnkerl]

@vapniks

• More Miller 6 doc info #849
• https://miller.readthedocs.io/en/latest/new-in-miller-6/#emit-statements
• https://miller.readthedocs.io/en/latest/reference-dsl-output-statements/#emit1-and-emitemitpemitf

[vapniks]

Yes, sounds OK to me. However the example you give for mlr5 also works with mlr 6:

$ mlr -n put 'end {@in={"a":1}; emit {"in":@in["a"]}}'
in
1

Maybe also include this example which works with mlr5 but not mlr 6:

$ mlr -n put 'end {@in={"a":1}; emit @in["a"]}' 
mlr: cannot parse DSL expression.
Parse error on token "[" at line 1 columnn 27.
Please check for missing semicolon.
Expected one of:
  ; } ,

Btw, there's a typo in the above output: it should be "column" not "columnn".
I also noticed a couple of minor typos in the documentation. I've submitted some pull requests to fix them.

[johnkerl]

Sorry @vapniks I wasn't clear

mlr -n put 'end {@in={"a":1}; emit @in["a"]}' 

This works in Miller 5 but not Miller 6, and it won't. I'll make it clear that this syntax is no longer supported.

$ mlr -n put 'end {@in={"a":1}; emit {"in":@in["a"]}}'

Yes, this works in Miller 5 & 6. I'll make it clear that this is the suggested workaround for the previous.

[johnkerl]

#858

Thanks again @vapniks ! :)