Regexes are stateful

[j201]

With Elm 0.14.1, running find on a regex changes its state, possibly causing future calls to find to act differently. It looks like this is because find uses JavaScript's re.exec, which sets the lastIndex property on the regex and makes it ignore matches before that index.

Example:

let re = regex "\\d"
    matchStr = foldl String.append "" << map .match
in [matchStr <| find (AtMost 1) re "1",
    matchStr <| find (AtMost 1) re "1",
    toString <| contains re "1",
    matchStr <| find (AtMost 1) re "1"]

Produces
["1","","True","1"]

The first find probably sets lastIndex to 1, making it ignore the match in the second find. contains calls str.match(re), which clears the regex state, making the last find work.

[evancz]

I think there was a PR that fixes this. Can you take a look at the history of Regex.js to see?

[evancz]

I think there was a PR that fixes this. Can you take a look at the history of Regex.js to see?

[nathan]

It looks like https://github.com/elm-lang/core/pull/156 fixed this.

[nathan]

It looks like https://github.com/elm-lang/core/pull/156 fixed this.

[evancz]

Cool, thanks for finding it @nathan! Let's close this until it can be reproduced with the latest version of the Regex library.

[evancz]

Cool, thanks for finding it @nathan! Let's close this until it can be reproduced with the latest version of the Regex library.