How to make an identifier NOT a keyword (dgrammar wrongly rejects keyword as prefix)

[timotheecour]

in pegged/examples/dgrammar.d there is:
Identifier <~ !Keyword [a-zA-Z_] [a-zA-Z0-9_]*
Keyword < "abstract" / "alias" ...

This rules out valid identifiers that use a keyword as a prefix (eg: int abstract_val=0), so this is incorrect.
Is there a better way?

Could the following be made to work? (where '\b' represents word break)

Identifier <~ !(Keyword '\b') [a-zA-Z_] [a-zA-Z0-9_]*
Keyword < "abstract" / "alias" ...

Could we generalize this to specify custom 'word breaks' using arbitrary regular expressions?

[timotheecour]

Answering my own question:

Identifier <~ !(Keyword WordBreak) [a-zA-Z_] [a-zA-Z0-9_]*
WordBreak <- ![a-zA-Z0-9_]
Keyword < "abstract" / "alias" ...

seems to work.

perhaps dgrammar could be updated with this?

[PhilippeSigaud]

Or !(Keyword Spacing) maybe?

I admit not using Pegged for quite some time. Does dgrammar generate OK? At
some time it was far too big for the CTFE engine.

On Mon, Jan 26, 2015 at 7:23 AM, Timothee Cour [email protected]
wrote:

Answering my own question:

Identifier <~ !(Keyword WordBreak) [a-zA-Z_] [a-zA-Z0-9_]*
WordBreak <- ![a-zA-Z0-9_]
Keyword < "abstract" / "alias" ...

seems to work.

perhaps dgrammar could be updated with this?

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#147 (comment)
.

[timotheecour]

haven't tried rencently, but it'd be useful to fix grammars for correctness
btw what's the difference bw 'foo' and "foo" ?

[PhilippeSigaud]

On Wed, Jan 28, 2015 at 10:57 PM, Timothee Cour [email protected]
wrote:

haven't tried rencently, but it'd be useful to fix grammars for
correctness
btw what's the difference bw 'foo' and "foo" ?

None at all. The creator of PEGs needed two ways to create terminals, to be
able to define both " and ' as possible terminals (that is, to define Rule
<- '"' and Rule <- "'").

[veelo]

Is there a better way?

I think there is: You can use semantic actions to filter out identifiers that are identical to keywords as I describe in #190 (comment). The actions can of course be defined in their own module that is included through the header instead of being defined in the header string.