Parse::RecDescent and AUTOSTUB

hagus has asked for the wisdom of the Perl Monks concerning the following question:

I've been playing with a little grammar here to parse SQL "CREATE TABLE" syntax:

my $grammar = q{
   startrule:              create_table_syntax
   create_table_syntax:    'CREATE TABLE' '(' column_definition(s /,/)
+ ')'
   column_definition:      column_name data_type column_attributes(?)
   column_name:            /\w+/
   data_type:             "INT" | "VARCHAR"
   column_attributes:     key_or_not_null
   key_or_not_null:       primary(?) 'KEY'
}
[download]

At the moment I'm experimenting with AUTOSTUB to get the key_or_not_null bit working. In BNF it looks like:

<key_or_not_null_spec> ::= 
  [PRIMARY] KEY 
| NOT NULL [WITH DEFAULT]
[download]

As I understand it, the square braces around PRIMARY indicate that it can be matched "zero or one" times. So I tried "primary"(?) in PRD grammar and that bombed. Now I'm trying primary(?) with AUTOSTUB turned on and that's bombing too. I really don't want to have to make a subrule that just says:

primary:    'primary'
[download]

But I don't really like the idea of using AUTOSTUB either - it seems kludgy. Ideally I want to be able to say "match this literal string zero or one times". Should I use a regex? Or is there some PRD grammar wisdom that I'm missing?

--
Ash OS durbatulk, ash OS gimbatul,
Ash OS thrakatulk, agh burzum-ishi krimpatul!
Uzg-Microsoft-ishi amal fauthut burguuli.

Comment on Parse::RecDescent and AUTOSTUB Select or Download Code

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Re: Parse::RecDescent and AUTOSTUB by Abigail-II (Bishop) on Jan 29, 2004 at 09:24 UTC
You should be able to do `key_or_not_null: "primary"(?) "KEY"` [download] Or you can write it with a regexp: `key_or_not_null: /(?:primary)?/ "KEY"` [download] Or even: `key_or_not_null: "PRIMARY KEY" \| "KEY"` [download] Abigail	[reply] [d/l] [select]
Re: Re: Parse::RecDescent and AUTOSTUB by hagus (Monk) on Jan 29, 2004 at 23:21 UTC
Me hearties, it be a fine piece o' code. But ye canna write: `my $grammar = q { startrule: test test: "primary"(?) "key" };` [download] Cause ye gets an error! Arr! `ERROR (line 4): Untranslatable item encountered: "?" (Hint: Did you misspell "?" or forget to comment it ou +t?)` [download] RD_TRACE told me: Parse::RecDescent: Treating "startrule:" as a rule declaration Parse::RecDescent: Treating "test" as a subrule match Parse::RecDescent: Treating "test:" as a rule declaration Parse::RecDescent: Treating ""primary"" as an interpolated literal terminal Parse::RecDescent: Treating "( ? )" as an implicit subrule Parse::RecDescent: Treating "_alternation_1_of_production_1_of_rul +e_test :" as a rule declaration ERROR (line 4): Untranslatable item encountered: "?" (Hint: Did you misspell "?" or forget to comment it ou +t?) Parse::RecDescent: Treating "_alternation_1_of_production_1_of_rul +e_test" as a subrule match Parse::RecDescent: Treating ""key"" as an interpolated literal ter +minal [download] Arr. -- Ash OS durbatulk, ash OS gimbatul, Ash OS thrakatulk, agh burzum-ishi krimpatul! Uzg-Microsoft-ishi amal fauthut burguuli.	[reply] [d/l] [select]
Re: Parse::RecDescent and AUTOSTUB by Abigail-II (Bishop) on Jan 29, 2004 at 23:24 UTC
Sure, but you can write: `test: ("primary")(?) "key"` [download] Abigail	[reply] [d/l]
Re: Re: Parse::RecDescent and AUTOSTUB by hagus (Monk) on Jan 29, 2004 at 23:57 UTC
Re: Parse::RecDescent and AUTOSTUB by allolex (Curate) on Jan 29, 2004 at 15:25 UTC
Abigail-II has it right (of course). The point is that PRD recognizes unquoted strings in subrules as productions. If you set `$RD_HINT = 1` at the beginning of the script, PRD should tell you that a production has no matching rule, or something of the sort. Alternatively, you could look at the output from code run with the RD_TRACE flag set. -- Allolex	[reply] [d/l]
Re: Parse::RecDescent and AUTOSTUB by Stevie-O (Friar) on Jan 29, 2004 at 23:09 UTC
You need to code it like this: `key_or_not_null: ('primary')(?) 'key' \| 'not' 'null' # if you put 'not null' then it won't gr +ok things with two spaces` [download] Also, there are other things to keep in mind: By default (i.e. if you're not using autoaction) each item evaluates to the last object on its line. That means your 'key_or_not_null' will return 'KEY'. Doing that ('primary')(?) thing still makes a new rule, it's jut that P::RD makes the rule for you (naming it 'anonymous_subrule_1_of_production_1_of_key_or_not_null' or something similar). This is because P::RD can't backtrack within a rule (so it can't backtrack if it doesn't match the word 'primary'). You probably want to use something like this: `key_or_not_null: m/primary\|/i 'KEY'` [download] Using a regex with /i gives it proper case-insensitivity (as SQL is case-insensitive for its keywords) That won't fork off into a second subrule. Instead, $item[1] will be either 'primary' or '' to indicate the absence of the word 'primary'. --Stevie-O `$"=$,,$_=q>\|\p4<6 8p<M/_\|<('=> .q>.<4-KI<l\|2$<6%s!<qn#F<>;$, .=pack'N',"@{[unpack'C',$_] }"for split/</;$_=$,,y[A-Z a-z] {}cd;print lc` [download]	[reply] [d/l] [select]