[Ticket #2393] Text.PrettyPrint.HughesPJ: Bug fixes, performance improvement

[Neil Mitchell]

Hi Benedikt,

Great work, and many thanks!

One ticket that might be interesting, while you are in the area, is:

http://hackage.haskell.org/trac/ghc/ticket/1217

The code is attached, I went through all the API review months and
months ago, and everyone agreed that the function should be added, but
under the name "zeroWidthText".

I'm guessing it isn't too much effort to tack this on while you are
working on it? I am currently limited to Hugs only (not enough disk
space to install GHC and no SSH access...), so am unable to patch any
libraries myself.

Thanks

Neil


On 6/24/08, Simon Peyton-Jones <simonpj at microsoft.com> wrote:
> Thank you for doing this Benedict.  I've added your more detailed comments to ticket #2393 so that they are preserved.
>
>  Ian: would you like to apply?  I'm not sure how to integrate the QuickCheck tests, but I bet you know.
>
>
>  Benedict: while you are in the area, would you like to take a swing at http://hackage.haskell.org/trac/ghc/ticket/1337, and 1176?
>
>  Simon
>
>
>
>  | -----Original Message-----
>  | From: libraries-bounces at haskell.org [mailto:libraries-bounces at haskell.org] On Behalf Of Benedikt Huber
>  | Sent: 24 June 2008 13:12
>  | To: libraries at haskell.org
>  | Subject: [Ticket #2393] Text.PrettyPrint.HughesPJ: Bug fixes, performance improvement
>  |
>  | Hello,
>  |
>  | I'd like to propose bugfixes, documentation fixes and a performance
>  | improvement for Text.PrettyPrint.HughesPJ. The changes shouldn't
>  | effect the expected behaviour of the PP library.
>  |
>  | I've written a QuickCheck test suite for the pretty printer (to test
>  | the improvement), and found two bugs and some misconceptions/
>  | ambiguities in the documentation. Additionally, there is a
>  | microbenchmark for the suggested improvement.
>  | Both are available at http://code.haskell.org/~bhuber/Text/
>  | PrettyPrint/. Note that the QuickCheck tests need access to all top-
>  | level names in HughesPJ (i.e. ignore the export list).
>  |
>  | In summary, I propose to
>  | * fix a bug in fillNB and one in fillNB/sepNB
>  | * correct documentation on laws and invariants.
>  | * add more efficient implementations of vcat,hsep,hcat
>  |
>  | More specifically:
>  |
>  | (1) Bugfix fillNB: Additional case for  fillNB Empty (Empty : ys)
>  |
>  | (2) Bugfix [f](cat|sep): do not allow overlapping ($$) in vertical
>  | composition
>  |
>  | (3) Lazy implementations of vcat,hcat and hsep
>  |
>  | (4) Law <t2> isn't always true
>  |
>  | (5) Invariant 5 should be made stronger
>  |
>  | (6) Change the comment about negative indentation
>  |
>
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