Re: String != [Char]

On Sat, Mar 24, 2012 at 05:31:48PM -0400, Brandon Allbery wrote:

On Sat, Mar 24, 2012 at 16:16, Ian Lynagh wrote:

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On Sat, Mar 24, 2012 at 11:50:10AM -0700, Johan Tibell wrote:

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Using list-based operations on Strings are almost always wrong

Data.Text seems to think that many of them are worth reimplementing for Text. It looks like someone's systematically gone through Data.List. And in fact, very few functions there /don't/ look like they are directly equivalent to list functions.

I was under the impression they have been very carefully designed to do the right thing with characters represented by multiple codepoints, which is something the String version *cannot* do. It would help if Bryan were involved with this discussion, though. (I'm cc:ing him on this.) Since the whole point of Data.Text is to handle stuff like this properly I would be surprised if your assertion that

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upcase :: String -> String

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upcase = map toUpper

This is no more incorrect than upcase = Data.Text.map toUpper

is correct.

I don't see how it could do any better, given both use toUpper :: Char -> Char to do the hard work. That's why there is also a Data.Text.toUpper :: Text -> Text Based on a very quick skim I think that there are only 3 such functions in Data.Text (toCaseFold, toLower, toUpper), although the 3 justification functions may handle double-width characters properly. Anyway, my main point is that I don't think that either text or String should make it any easier for people to get things right. It's true that currently only text makes correct case-conversions easy, but only because no-one's written Data.String.to* yet. Thanks Ian