Defining a "followed by" operator or function in Ruby


#1

Hi all -
As part of doing a parsing lib in Ruby, I want to create a “followed
by” operator or function. In other words, I want to be able to specify
that (say) “foo” must be followed by n or more occurrences of “bar”.

Something like this -
“foo”.(0,+) “bar” would match zero or more occurrences of “foo” followed
by “bar”. So, it would match “foo” , “foo” “bar”, “foo” “bar” “bar” …
and so on.

“foo”.(0,1) “bar” would match zero or one occurrences of “foo” followed
by “bar”.

So, how could this be done?
Very many thanks in advance!

  • Andy

#2

Something like this -
“foo”.(0,+) “bar” would match zero or more occurrences of “foo” followed
by “bar”. So, it would match “foo” , “foo” “bar”, “foo” “bar” “bar” …
and so on.

“foo”.(0,1) “bar” would match zero or one occurrences of “foo” followed
by “bar”.

Are you talking about regular expression syntax?

(foo){0,}(bar){1,} # or (foo)?(bar)+
(foo){0,1}bar # or (foo)?bar

See http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html#UL

Otherwise, if you are writing a parser for some language of your own
devising, then you are free to implement whatever syntax you wish. Buy a
good book on language and compiler design.


#3

Brian C. wrote:

Something like this -
“foo”.(0,+) “bar” would match zero or more occurrences of “foo” followed
by “bar”. So, it would match “foo” , “foo” “bar”, “foo” “bar” “bar” …
and so on.

“foo”.(0,1) “bar” would match zero or one occurrences of “foo” followed
by “bar”.

Are you talking about regular expression syntax?

(foo){0,}(bar){1,} # or (foo)?(bar)+
(foo){0,1}bar # or (foo)?bar

See http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html#UL

Otherwise, if you are writing a parser for some language of your own
devising, then you are free to implement whatever syntax you wish. Buy a
good book on language and compiler design.
Hi Brian -
Thanks very much for that - it should be a big help!
Bye for now -

  • Andy