Re: [Haskell-cafe] Why is $ right associative instead ofleftassociative?

John Hughes wrote:

...

Quoting Paul Hudak :

...

Actually, one of the main reasons that we chose (:) is that that's what Miranda used. So, at the time at least, it was not entirely clear what the "de facto universal inter-language standard" was.

Phil Wadler argued for the ML convention at the time, and wrote a document containing a fair amount of sample code to illustrate what it would look like. We noticed something surprising: instead of (x:xs) and the like, Phil had consistently written (x :: xs) -- note the extra spaces. Somehow, using the longer operator name led him to feel spaces were needed around it. That in turn made his lines longer, encouraged him to split definitions across lines, and so on. When I read the thing, I realised after a while that I was skipping all the code fragments -- because they just looked too big and complicated to take in during a quick reading. It was at least partly that experience that convinced us that using :: for cons would impose a small cost, but a real one, on readability. It may seem trivial, but the sum of many such decisions is significant. The story does illustrate the importance of actually trying out syntactic ideas and seeing how they play--one can be surprised by the result.

And at the time I agreed with you. But now I'm older and wiser(?). I now think :: for type signatures was a bad mistake. I don't use lists very much. They are not the right data structure for many things. So : is not as common as :: in my code. I checked a small sample of code, about 20000 lines of Haskell. It has about 1000 uses of ':' and 2000 of '::'. In my opinion all the special syntactic sugar for lists should go away. I don't think lists are special enough to motivate it. But this is not what Haskell' is about. It's supposed to be some modest extensions to Haskell. Not designing a new perfect language. -- Lennart