lastIndexOf' with index greater than string length returns Nothing

[hdgarrood]

In the JavaScript API, the fromIndex parameter in str.lastIndexOf(pattern [, fromIndex]), perhaps surprisingly, represents the index at which to stop searching (if we imagine the search proceeds from left-to-right). This means that if you provide a fromIndex which is greater than or equal to the string's length, in JS, it's equivalent to searching the whole string, i.e. not specifying that parameter at all. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/lastIndexOf

However, in this library, the bounds check in lastIndexOf' means that e.g. lastIndexOf' (Pattern "a") 3 "aa" comes out as Nothing. I'd suggest getting rid of this check entirely, so that this matches better with the JS behaviour. This is a breaking change unfortunately.

Incidentally there are one or two other breaking changes I'd like to do (#81, #78, and also renaming Data.String.CodePoints to Data.String and renaming Data.String to Data.String.CodeUnits) so maybe we could do all of these the next time we break everything (i.e. when we release 0.12?)

[hdgarrood]

Previous discussion: #55.

[hdgarrood]

Can we do this as part of the updates for 0.14?

[garyb]

This is one of those sneaky hidden breaking changes that isn't communicated in the types, it's a shame there's not a good way of knowing how much code this is likely to affect 😕

[hdgarrood]

I think this is such a weird behaviour that someone almost certainly would have opened an issue by now if they had actually run into it.