Dear George, Am Dienstag, den 13.12.2016, 12:24 +0000 schrieb George Colpitts:
I got confused; when I I google "haskell list length" I end up at https://hackage.haskell.org/package/base-4.9.0.0/docs/Data-List.html. When I look at the source code for length by clicking on "Source" It takes me to the start of the file https://hackage.haskell.org/package /base-4.9.0.0/docs/src/Data.Foldable.html#length. instead of the definition of length in https://hackage.haskell.org/package/base-4.9. 0.0/docs/src/GHC.List.html#length.
To me, this seems like a bug in haddock. In Data.List.html when I click on the source code for init I go to https://hackage.haskell.org /package/base-4.9.0.0/docs/src/GHC.List.html#init. This is the file I should go to for the source code for length also. Perhaps the problem is that the type of length in Data.List is Foldable t => t a -> Int while init is [a] -> [a] ? Should I file a haddock bug for the preceding?
not, this is all right and intentional. Data.List re-exports Data.Foldable.length so that you do not get import conflicts when importing both. This was a design decision back then when the FTP (Foldable/Traversable) proposal was enacted.
There seems to be two minor related problems with the Users Guide (8.0.1.20161117) in section 10.32.6,List fusion. First, it should mention length as a good consumer. Secondly, it says: "If you want to write your own good consumers or producers, look at the Prelude definitions of the above functions to see how to do so." However if you go to https://hackage.haskell.org/package/base- 4.9.0.0/docs/Prelude.html and look at the source code for length you end up at https://hackage.haskell.org/package/base- 4.9.0.0/docs/src/Data.Foldable.html#length which is not a good consumer. I think the User's Guide should be changed to replace "Prelude" with "Data.List" in the quoted sentence. I'll file a doc bug on the User's Guide for these two issues.
Yes, that would be helpful. The text has not been added since FTP. Maybe even better, the user’s guide could simply contain a section that explains how to make good consumers and producer, including the hoops that one has to jump through when one wants to use the library’s version of a function when no fusion happens. Maybe together with David Feuer, who most recently battled with that. Maybe I can write that, I just had to write about list fusion for a paper anyways. Greetings, Joachim -- Joachim “nomeata” Breitner mail@joachim-breitner.de • https://www.joachim-breitner.de/ XMPP: nomeata@joachim-breitner.de • OpenPGP-Key: 0xF0FBF51F Debian Developer: nomeata@debian.org