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Implement Absent Operator #82

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k-takata opened this issue Dec 14, 2016 · 5 comments
Closed

Implement Absent Operator #82

k-takata opened this issue Dec 14, 2016 · 5 comments
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@k-takata
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@k-takata k-takata commented Dec 14, 2016

Slide and paper by Akira Tanaka (@akr) (both Japanese):

TODO:

  • Syntax:
    Maybe the form of (?...) should be used. For example (?~...)?
  • Implementation:
    Is it easy?
@k-takata
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@k-takata k-takata commented Dec 15, 2016

Akira's paper says that look-ahead assertion doesn't have theoretical backgrounds. However @sinya8282 says that look-ahead assertion is a regular expression (in context of formal language theory), and it can be proved by using boolean automaton.
Then absent operator can be a syntax sugar of (?:(?!expr)(?m:.))*?

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@k-takata k-takata commented Dec 15, 2016

It seems that (?~expr) is different from (?:(?!expr).)*.
\A(?~abc)c should match abc (because (?~abc) matches ab), but \A(?:(?!abc).)*c doesn't match.

https://twitter.com/nalsh/status/809375869626150912

k-takata added a commit that referenced this issue Dec 22, 2016
k-takata added a commit that referenced this issue Dec 23, 2016
(?~subexp) matches any string which doesn't have subexp as its suffix.

This is based on Tanaka Akira's paper and slide:
* https://staff.aist.go.jp/tanaka-akira/pub/prosym49-akr-paper.pdf
* https://staff.aist.go.jp/tanaka-akira/pub/prosym49-akr-presen.pdf
k-takata added a commit that referenced this issue Dec 23, 2016
k-takata added a commit that referenced this issue Dec 23, 2016
@k-takata k-takata added the todo label Dec 23, 2016
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@k-takata k-takata commented Dec 23, 2016

topic/absent-operator branch was merged into the master branch.
Maybe more tests are needed, but closing for now.

@k-takata k-takata closed this Dec 23, 2016
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@k-takata k-takata commented Dec 25, 2016

However @sinya8282 says that look-ahead assertion is a regular expression

This is discussed in a paper by Akimasa MORIHATA:

hsbt pushed a commit to ruby/ruby that referenced this issue Feb 11, 2017
* Support absent operator k-takata/Onigmo#82
* https://github.com/k-takata/Onigmo/blob/Onigmo-6.1.1/HISTORY

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57603 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
hsbt pushed a commit to ruby/ruby that referenced this issue Mar 13, 2017
	Merge Onigmo 6.1.1

	* Support absent operator k-takata/Onigmo#82
	* https://github.com/k-takata/Onigmo/blob/Onigmo-6.1.1/HISTORY

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@57957 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
@headius headius mentioned this issue Dec 1, 2017
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@headius headius mentioned this issue Mar 27, 2018
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