Use slices instead of cursors

[chtenb]

Proof of concept to fix #77. This change would be breaking because it changes the underlying representation.

• Use slices instead of cursors
• Do a startsWith check in the string parser instead of a call to indexOf
• Make the CodePoint parsers anyDigit, anyLetter and derivatives use the CodeUnit version of anyChar for speed
• Added the change to the changelog's "Unreleased" section with a link to this PR and your username
• Linked any existing issues or proposals that this pull request should close

Benchmark before	Benchmark after
StringParser.runParser parse23AnyCharPoints	StringParser.runParser parse23AnyCharPoints
mean = 1.01 s	mean = 16.14 ms
stddev = 51.48 ms	stddev = 13.64 ms
min = 963.28 ms	min = 8.55 ms
max = 1.16 s	max = 53.29 ms
StringParser.runParser parse23AnyCharUnits	StringParser.runParser parse23AnyCharUnits
mean = 8.53 ms	mean = 8.73 ms
stddev = 2.77 ms	stddev = 2.95 ms
min = 7.25 ms	min = 7.24 ms
max = 38.72 ms	max = 40.49 ms
StringParser.runParser parse23DigitPoints	StringParser.runParser parse23DigitPoints
mean = 994.93 ms	mean = 10.02 ms
stddev = 16.97 ms	stddev = 1.61 ms
min = 974.33 ms	min = 8.65 ms
max = 1.04 s	max = 23.21 ms
StringParser.runParser parse23DigitUnits	StringParser.runParser parse23DigitUnits
mean = 10.87 ms	mean = 10.28 ms
stddev = 1.78 ms	stddev = 1.56 ms
min = 9.51 ms	min = 8.71 ms
max = 23.81 ms	max = 22.51 ms
StringParser.runParser parse23StringPoints	StringParser.runParser parse23StringPoints
mean = 1.06 s	mean = 6.91 ms
stddev = 16.93 ms	stddev = 954.29 μs
min = 1.01 s	min = 5.80 ms
max = 1.09 s	max = 15.04 ms
StringParser.runParser parse23StringUnits	StringParser.runParser parse23StringUnits
mean = 4.52 ms	mean = 4.40 ms
stddev = 958.15 μs	stddev = 757.47 μs
min = 3.81 ms	min = 3.61 ms
max = 13.09 ms	max = 8.46 ms
StringParser.runParser parse23RegexPoints	StringParser.runParser parse23RegexPoints
mean = 1.03 s	mean = 11.77 ms
stddev = 44.87 ms	stddev = 2.11 ms
min = 978.55 ms	min = 9.76 ms
max = 1.15 s	max = 28.49 ms
StringParser.runParser parse23RegexUnits	StringParser.runParser parse23RegexUnits
mean = 5.90 ms	mean = 5.88 ms
stddev = 900.33 μs	stddev = 1.05 ms
min = 4.89 ms	min = 4.93 ms
max = 12.99 ms	max = 16.71 m

[chtenb]

We can close purescript/purescript-strings#155 once this PR gets merged

[jamesdbrock]

Nice, I will look at this.

[jamesdbrock]

Why is this a breaking change, besides changing the names of the record fields in PosString?

[jamesdbrock]

So here we're in the CodePoints parser, but I think this says that any astral CodePoint is not allowed? Is that what we want?

[jamesdbrock]

I mean it's true that because this parser returns Char there is no way for it to parse an astral CodePoint.

But I think this will surprise and confuse people? Maybe the CodePoints parsing module should not include this parser?

[chtenb]

Yeah, I agree with you. I'm in favour of exporting an anyCodePoint instead or something in this module. I think the Char type is not a useful abstraction in PureScript (at least, it shouldn't be), but perhaps we should also keep supporting the anyChar parser as long as Char is a thing? I think it also depends on what direction purescript/purescript#3662 is taking.

[chtenb]

Why is this a breaking change, besides changing the names of the record fields in PosString?

Because the Parser type has changed and it is part of the public API of this package. If people have written a parser in terms of this definition, their code will have to be adjusted. Or does that not qualify as a breaking change?

[jamesdbrock]

Because the Parser type has changed and it is part of the public API of this package.

Sure, that makes sense. But the only thing that has changed about the type of the Parser is the record field names in PosString, right?

If it were up to me, I think I would do the work you've already done, and then also

1. add anyCodePoint :: Parser CodePoint
2. Document that anyChar will not always succeed, like here https://pursuit.purescript.org/packages/purescript-parsing/8.2.0/docs/Text.Parsing.Parser.String#v:anyChar

[chtenb]

But the only thing that has changed about the type of the Parser is the record field names in PosString, right?

Yes

I'll make an issue for anyCodePoint