On 1 April 2017 at 19:42, Henrik Nilsson
Hi all,
It is perfectly to limit the concept of "length" to
* linear structures (lists, arrays, etc.) [branching structures do not have a length, they may have a size or maximum depth]
* which have variable length [why would you otherwise ask for the length?]
Just for the record, I could not agree more.
Looking up "length", e.g. Merriam-Webster:
1a : the longer or longest dimension of an object
What we really are talking about here is counting the number of elements in a data structure. That is clearly applicable to lists as well as trees and tuples interpreted in particular ways.
But calling it "length" is not particularly helpful. Nor the effort to reappropriate the very concept of "length" through a categorical interpretation.
It would have been a lot better if a name suggesting a sense of counting, or at least a name suggesting that this is something different than the usual length, would have been picked. Maybe elementcount or ever flength.
I agree, but on the other hand this should have been done _before_ FTP; at this stage, I lean towards marking this down as one of the known warts of Haskell - possibly with a 3 major version GHC cycle to migrate to a better name once the bikeshedding has been completed - and moving on rather than being revisionist and using this as an excuse to go backwards. So far, the arguments against these instances that I've seen are: * The name of the length function is misleading for such instances (with all respect to Tony, agreed; but see above); I don't think I've seen anyone else complain about any of the other function names though. * Since these classes/instances are now exported from the Prelude, previous code that wouldn't have have type-checked are now valid and thus produce unexpected results (I was against the Prelude export when FTP was being debated, but now - with the possible exception of people learning to program - I think this is a matter of needing to be more aware of the types and using our wonderful REPL environments to test functions rather than blindly just writing code without validating the code logic). TL;DR: I didn't 100% agree with the way FTP was done precisely due to the problems people have with these instances, but now let's not go backwards (and the tuple instances I've found very useful).
Names matter.
/Henrik
This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham.
This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.
_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com