CodePoints.uncons performance optimization?

[jamesdbrock]

It seems to me that these lines in Data.String.CodePoints.uncons

purescript-strings/src/Data/String/CodePoints.purs

Lines 197 to 198 in 157e372

	cu0 = fromEnum (Unsafe.charAt 0 s)
	cu1 = fromEnum (Unsafe.charAt 1 s)

are first slicing the first code unit into a Char string with the JavaScript charAt method

purescript-strings/src/Data/String/Unsafe.js

Line 5 in 157e372

if (i >= 0 && i < s.length) return s.charAt(i);

and then converting the Char string to a CodePoint by the boundedEnumChar instance fromEnum method which calls the Javascript charCodeAt method.

https://github.com/purescript/purescript-enums/blob/170d959644eb99e0025f4ab2e38f5f132fd85fa4/src/Data/Enum.js#L4

We could skip the intermediate string slice of the charAt method and call charCodeAt directly.

[JordanMartinez]

Is it doing that because it makes it easier on other backends?

[jamesdbrock]

Is it doing that because it makes it easier on other backends?

Maybe. That's a good point.

[jamesdbrock]

I tried swapping in a “fast” CodePoints.uncons function in purescript-parsing and couldn't detect any speedup.