simplify type of replace'

[davidchambers]

Commit message:

The match argument provided by String#replace (when given a function) is often irrelevant. If one does require access to the matched substring as a whole, one can parenthesize the whole pattern to capture it.

This is a breaking change, but I believe it would make replace' slightly more user-friendly.

This proposal was conceived while considering sanctuary-js/sanctuary#685 (as was #126).

[JordanMartinez]

@kl0tl Thoughts on this one? You reviewed David's prior PR.

[MonoidMusician]

I understand your point that "one can parenthesize the whole pattern to capture [the matched substring]", but I think in cases where the user really does need access to the whole match, having to deal with the partiality of getting it from the array of matches might be annoying, so it's not quite a free change. Plus there might be cases where you actually don't have access to the regex, if it's coming from a library or something.

[davidchambers]

Very good points, @MonoidMusician.

in cases where the user really does need access to the whole match, having to deal with the partiality of getting it from the array of matches might be annoying

True. There is value in treating the whole match specially for this reason.

This highlights the impreciseness of the type we are using to represent captured substrings. Consider the regular expression ^(http(s)?)://. Array (Maybe String) is misleading for two reasons: the number of capturing groups is fixed, and the first capturing group is not optional. Ideally the type would be (String, Maybe String) in this case, but this would require parsing regular expressions to determine the number of capturing groups and their optionality.

I am not suggesting that we change the type of the captured substrings; Array (Maybe String) is a pragmatic approximation. It is unfortunate that extracting substrings from required capturing groups requires the use of a partial function (fromJust) or a dummy default value (fromMaybe 'XXX').

Plus there might be cases where you actually don't have access to the regex, if it's coming from a library or something.

I considered this in sanctuary-js/sanctuary#685, but the circumstances differ: JavaScript libraries can focus on common use cases because the underlying APIs are always available. What is right for Sanctuary may not be right for PureScript.

[kl0tl]

I don’t have a strong opinion on this but I don’t think that ignoring the first argument of the replacer function is annoying enough to warrant a breaking change. This would be perhaps more appropriate in an opinionated regex library.

[davidchambers]

Thank you for considering this change. :)