Understanding PetitParser2 behavior

Question

I'm struggling with a small parser using PetitParser2. Here is a fragment of some of the rules I'm defining but their behaviour is not as I could expect:

andKeyword := 'and' asPParser trim, #letter asPParser not. notKeyword := 'not' asPParser trim, #letter asPParser not. keyword := andKeyword / notKeyword. nonKeywordIdentifier := keyword not, #letter asPParser, #word asPParser star. word := nonKeywordIdentifier, #blank asPParser star. words := word star.

The behaviour of the "nonKeywordIdentifier" is the expected:

identifier end parse: 'hello'. "It parses successfully" identifier end parse: 'and'. "It fails as 'and' is a keyword"

However the "words" rule's behavior is the following:

words end parse: 'hello Pharo'. "It parses successfully" words end parse: 'hello and bye'. "It parses, when I would expect it fails because 'and' is a keyword"

I don't understand why the "words" rule works this way, but I'm starting with PetitParser. Any suggestions?

PS: Sorry for the cross-posting in the Pharo users mailing list.

Thank you.

tukan · Accepted Answer · 2024-09-05 14:18:31Z

words end parse: 'hello and bye'. "It parses, when I would expect it fails because 'and' is a keyword"

nonKeywordIdentifier := keyword not, #letter asPParser, #word asPParser star. word := nonKeywordIdentifier, #blank asPParser star. words := word star.

It parses because you have created a loop. word calling nonKeywordIdentifier and the other way around. Even thou you have only #letter asPParser, but that will be matched #word asPParser star times (notice the star at the end).

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