Summary: Haskell uses :: as the type operator. That was a mistake that costs us over 1 million characters of source code.
Haskell uses :: for type annotations, e.g. (1 :: Int). Most other FP languages with types use :, including Scala, OCaml, Agda, Idris and Elm. Haskell uses : for list cons, so you can write:
myList = 1:2:[] :: [Int]
Whereas in other languages you write:
myList = 1::2::[] : [Int]
Moreover, the reason Haskell preferred :: was the belief that if the cons operator was :: then people would quite naturally insert spaces around it, giving:
myList = 1 :: 2 :: [] : [Int]
The final program is now noticeably longer than the original. Back when people first invented Haskell, I imagine they were mainly list manipulation operations, whereas now plenty of libraries work mainly at the type level. That raises the question - would Hackage be shorter or longer if we used : for types?
Method
I downloaded the latest version of every Hackage package. For each .hs file, I excluded comments and strings, then counted the number of instances of : and ::, also noting whether there were spaces around the :. The code I used can be found here.
Results
- Instances of
::= 1,991,631 - Instances of
:= 265,880 (of which 79,109 were surrounded by two spaces, and 26,931 had one space)
Discussion
Assuming we didn't add/remove any spaces, switching the symbols would have saved 1,725,751 characters. If we assume that everyone would have written :: with spaces, that saving drops to 137,9140 characters. These numbers are fairly small, representing about 0.17% of the total 993,793,866 characters on Hackage.
Conclusion
The Haskell creators were wrong in their assumptions - type should have been :.
Update: the first version of this post had numbers that were too low due to a few bugs, now fixed.
5 comments:
Thank you for this empirical confirmation of my long-held belief. I only regret that in posting now, you may have missed the chance for a 1 April Haskell Prime proposal.
Daniel: This feature is so great that I'm not sure we can wait til 1st April for the proposal.
I put this post in my Hall of Fame of parodies.
Especially liked the "0.17%" note ;-).
...and has been duly noted at https://wiki.haskell.org/Nitpicks.
to Mr David Turner;
Could you please enlighten the rest of us, and future generations, as to why you used a single colon for the cons data constructor in Miranda(R) (along with - IIRC - SASL and KRC)?
I'm assuming that choice was one crucial factor in Haskell now having the same syntax.
Thank you.
Thank you foor writing this
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