Comments on: Applicative Functors in Scala

By: Daniel Spiewak

Daniel Spiewak — Sat, 21 Jun 2008 19:05:03 +0000

Boy, you Haskell veterans…can’t get you to do anything that isn’t cryptic!
I’m not sure I understand why the fixity of the operator is an issue. All of the operators in your example are infix; you’re not using anything unary or anything like that. If your operators were all right-associative, the resulting AST would be the same as it is now with left-associative operators and parentheses. (wouldn’t it?)

By: Tony Morris

Tony Morris — Fri, 20 Jun 2008 02:46:31 +0000

Hi Daniel,
I prefer the former definition for add. Actually, I prefer the less clumsy:

val add = curried((_: Int) + (_: Int) + (_: Int))

However, I didn’t want to take away from the example
Using a colon as a function name suffix only alters the associativity, not the fixity of the function — parentheses would still be required (in fact, I have a function called <*>: and I could show this if you like).

The type of None is Option[Nothing] and the type inferencer requires a type Option[Int] at that point because of the method used in inferencing (a forward inferencer). You’re more than welcome to try it and see. The code at hand can be found at http://projects.workingmouse.com/public/scalaz/branches/3.0/

As a general rule, whenever you try to do anything powerful with Scala, you find the type inferencer starts to let you down quite quickly.

By: Daniel Spiewak

Daniel Spiewak — Fri, 20 Jun 2008 02:07:26 +0000

Oh, if you use right-associative operators, I think you can get rid of your none: Option[Int] and just use None (since you no longer need to “dispatch” on its type).

By: Daniel Spiewak

Daniel Spiewak — Fri, 20 Jun 2008 02:02:26 +0000

BTW, you can make the definition of *add* a lot more concise with the semantically-equivalent:

def add(a: Int)(b: Int)(c: Int) = a + b + c

Fewer arrows, anyway. Also, if you really need right-associativity, you can suffix your operators with a colon (:). It’s ugly, but it does the trick.