Haskell Platform Proposal: add the 'text' library

wren ng thornton wren at community.haskell.org
Fri Sep 10 17:03:35 EDT 2010

On 9/10/10 4:10 PM, Ian Lynagh wrote:
> On Thu, Sep 09, 2010 at 11:36:30AM -0700, Bryan O'Sullivan wrote:
>> On Wed, Sep 8, 2010 at 5:21 PM, wren ng thornton<wren at community.haskell.org
>>> wrote:
>>>> Text: break :: Text ->   Text ->   (Text, Text)
>>>>        breakBy :: (Char ->   Bool) ->   Text ->   (Text, Text)
>>> Other than that, I do agree with the philosophy of the "deliberate and
>>> sensible" differences. Though, given the philosophy that these aren't
>>> Char-wise operations, why does Text.breakBy accept a (Char->Bool)? Is this
>>> just an optimization for common cases like breaking on Unicode-defined
>>> whitespace codepoints?
>> I kept breakBy in there because it is actually useful. I changed its name
>> because it's by far less common than "I want to break on a string".
> That makes sense if considering text in isolation, but as part of a
> system I would prefer consistent names between []/String, bytestring and
> text. (It shouldn't necessarily be text that changes, though).
> I also wonder if there should be a
>      f :: (Text ->  Bool) ->  Text ->  (Text, Text)

Yes, that was my point. I can see uses for (Text->...), 
((Text->Bool)->...), and ((Char->Bool)->...) but the middle one ---which 
seems to be the closest analogue to String and ByteString--- is missing. 
The first one is posited as a replacement for the middle one, but it is 
insufficient since it cannot perform disjunctive searches. When I 
pointed that out, I was directed to the third one, which is insufficient 
because I may wish to search for "characters" which are not individual 

Why do we not just have the middle ((Text->Bool)->...) option? The other 
two options are subsumed by it, so the only reason to define them is (a) 
because they can be implemented more efficiently, or (b) as mere 
shorthands for doing the necessary coercions to turn the first argument 
into the right type of predicate.

Live well,

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