Re: Haskell Platform Proposal: add the 'text' library

On 20/10/2010, at 00:35, Duncan Coutts wrote:

On 19 October 2010 22:08, Roman Leshchinskiy wrote:

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On 19/10/2010, at 15:22, John Lato wrote:

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I think there's a significant difference between vector and text, namely a Vector is conceptually the same as a list/1D array, while a Text is not. I think this difference is enough to warrant a break from the list API.

Are you sure? From its interface Text looks exactly like a list of Chars to me.

Right, that's a very common misunderstanding of Unicode. A Unicode code point (type Char) does not correspond 1:1 with the human notion of a character.

True. But I didn't say it's a list of characters. It's a list of Chars, i.e., of Unicode code points.

It would be nice if it did, but unfortunately it is not something we can ignore. Because of this it is better not to think of operations on individual Chars but on short sequences of Chars. In any case, when processing text (even ASCII where Chars do match characters) many of the most common operations that you want are substring not element based.

So this is why a list/vector API is not necessarily appropriate for text.

But text *does* have a list API. It doesn't get any "listier" than uncons, foldr and unfoldr. From my point of view, if these functions make sense for the data type then it's a list. If it's not a list then these functions don't make sense and shouldn't be provided. Roman