PetitParser: Parse X as long as it's not Y

How do I tell Petit Parser to parse a string of certain allowable characters as long as the final result isn't a particular string? E.g. consume an identifier as long as it's not 'Baz' or 'Bar'

Thanks

vonbecmann wrote

did you try with negate?

That is the standard trick with PP, but the problem here is that I'm trying to say, not just "anything which is not Y", but "any string of these characters as long is it doesn't also match Y"

Hi, not sure if I understand your requirement, but you can try:

Y not, chars star

Is this what you need?

Cheers Jan

Sean

This seems to be what the PPAndParser is designed for. I tried the
following:

identifier := #letter asParser plus flatten.
exclusion := ('Bar' asParser / 'Baz' asParser) negate.
restricted := identifier and, exclusion.

restricted matches: 'abc'. "--> true"
restricted matches: 'Baz'. "--> false"

(Note the comma after 'and' is necessary - this wasted me a few minutes in
trying.)

Hope this helps

Peter Kenny

-----Original Message-----
From: Pharo-users [mailto:[hidden email]] On Behalf Of
Sean P. DeNigris
Sent: 05 August 2017 21:26
To: [hidden email]
Subject: [Pharo-users] PetitParser: Parse X as long as it's not Y

How do I tell Petit Parser to parse a string of certain allowable characters
as long as the final result isn't a particular string? E.g. consume an
identifier as long as it's not 'Baz' or 'Bar'

Thanks



-----
Cheers,
Sean
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Sean

A supplementary point I have just realised. The basic 'and' idea is correct,
but my example is over-simplified. As written, it will reject any string
beginning with 'Bar' or 'Baz'. If you use this pattern, you will need to be
careful how you define the exclusion.

Peter


-----Original Message-----
From: Pharo-users [mailto:[hidden email]] On Behalf Of
PBKResearch
Sent: 06 August 2017 13:28
To: 'Any question about pharo is welcome' <[hidden email]>
Subject: Re: [Pharo-users] PetitParser: Parse X as long as it's not Y

Sean

This seems to be what the PPAndParser is designed for. I tried the
following:

identifier := #letter asParser plus flatten.
exclusion := ('Bar' asParser / 'Baz' asParser) negate.
restricted := identifier and, exclusion.

restricted matches: 'abc'. "--> true"
restricted matches: 'Baz'. "--> false"

(Note the comma after 'and' is necessary - this wasted me a few minutes in
trying.)

Hope this helps

Peter Kenny

-----Original Message-----
From: Pharo-users [mailto:[hidden email]] On Behalf Of
Sean P. DeNigris
Sent: 05 August 2017 21:26
To: [hidden email]
Subject: [Pharo-users] PetitParser: Parse X as long as it's not Y

How do I tell Petit Parser to parse a string of certain allowable characters
as long as the final result isn't a particular string? E.g. consume an
identifier as long as it's not 'Baz' or 'Bar'

Thanks



-----
Cheers,
Sean
--
View this message in context:
http://forum.world.st/PetitParser-Parse-X-as-long-as-it-s-not-Y-tp4958895.ht
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Peter Kenny wrote

This seems to be what the PPAndParser is designed for.

Thanks for the pointer, Peter! I finally figured it out based on your example. To get more concrete, I'm trying to parse a name, where the end of the input might be an optional middle name, followed by an optional generational (e.g. 'Paul III'). What I think the restricted line says is: "peek to make sure we don't have a #gen, then try to parse an #identifier". Interestingly the order is important. If the peek and identifier are reversed, it tries to peek after the identifier, causing an error when there is only a middle name (i.e. no more input).

identifier := #letter asParser plus flatten.
gen := 'Jr' asParser / 'Sr' asParser.
restricted := gen negate and, identifier.
parser := ((#space asParser, restricted) optional, (#space asParser, gen) optional) end.
parser parse: ' Paul Jr'.
parser parse: ' Paul'.
parser parse: ' Jr'.

This really had me baffled. Thanks again!!

Sean

One extra point. You may need to post-process the parse to get what you
want. In the 'restricted' line, if you don't have a #gen then 'gen negate'
will have succeeded and will generate its own node in the parse - in your
example of ' Paul' as input it will be $P. Assuming you don't want this (!),
you can add ==> [:nodes| nodes second] to the definition of restricted.

I had realized this after I posted on Sunday, as well as the fact that I had
put the anded elements in the wrong order, but I didn't want to generate a
stream of supplementaries.

HTH

Peter

-----Original Message-----
From: Pharo-users [mailto:[hidden email]] On Behalf Of
Sean P. DeNigris
Sent: 09 August 2017 03:41
To: [hidden email]
Subject: Re: [Pharo-users] PetitParser: Parse X as long as it's not Y

Peter Kenny wrote
> This seems to be what the PPAndParser is designed for.

Thanks for the pointer, Peter! I finally figured it out based on your
example. To get more concrete, I'm trying to parse a name, where the end of
the input might be an optional middle name, followed by an optional
generational (e.g. 'Paul III'). What I think the restricted line says is:
"peek to make sure we don't have a #gen, then try to parse an #identifier".
Interestingly the order is important. If the peek and identifier are
reversed, it tries to peek after the identifier, causing an error when there
is only a middle name (i.e. no more input).

identifier := #letter asParser plus flatten.
gen := 'Jr' asParser / 'Sr' asParser.
restricted := gen negate and, identifier.
parser := ((#space asParser, restricted) optional, (#space asParser, gen)
optional) end.
parser parse: ' Paul Jr'.
parser parse: ' Paul'.
parser parse: ' Jr'.

This really had me baffled. Thanks again!!



-----
Cheers,
Sean
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Peter Kenny wrote

You may need to post-process the parse to get what you
want.

Good point. I omitted several ` ==> #second` in several places for readability on the list, but we should mention that for posterity. Also, duh `gen negate and` should be `gen not`!

Hi,

As Jan pointed out, you should use “not” instead of “negate and”.

Cheers,
Doru


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