4 ms·

Nice writeup. Although I really like the fact that lenses (from the `lens` package) can be composed using regular function composition, instead of the more gen

Nice writeup. Although I really like the fact that lenses (from the `lens` package) can be composed using regular function composition, instead of the more generalized category composition like `fclabels` uses, I still think it's weird that the direction of composition is flipped. I reads more like OO, but a lot less like idiomatic Haskell.

dons 13y ago
I strongly prefer the regular composition order. But I also use fclabels (FTW!) Changing the direction of composition makes no sense.
- tel 13y ago
  Composition order is the weirdest thing about Control.Lens.
- dan00 13y ago
  "Changing the direction of composition makes no sense." I also can't stand all these operators of the lens package. It feels like reading Perl code. The only annoying thing about all the other lens packages is the need for hiding '.' from Prelude.
boothead 13y ago
I thought that function composition (.) arises from the category instance for (->)? Actually on checking it seems that Prelude re-exports (.) from Data.Function. I'm sure I read somewhere that these had been unified, was I wrong?
- tome 13y ago
  I believe the argument against unifying is that you get very hard to decipher error messages.
crntaylor 13y ago
I also think it's a bit weird to flip direction of composition, but there are a couple of advantages -- 1. It keeps the "imperative" feel, so that you can write person.address.zipCode rather than zipCode.address.person 2. There's an argument that mathematical functions are "back to front" and that it would be more natural to write functions left to right, i.e. (x)f rather than f(x), so that the function composition f.g is "apply f then apply g" rather than "apply g then apply f" which is where we are at the moment.
- tel 13y ago
  Let's just go ahead and steal (<) and (>) for directional function composition everywhere. I'd rather just write `lt` and `gt`. x & f > g > h === h < g < f $ x
  - tome 13y ago
    We already have (<<<) and (>>>) so you're nearly there :)
    - tel 13y ago
      Those always feel comical to use to me. It's like having a 747 landing strip to help guide a duck in for a safe landing.
      - tome 13y ago
        Yes they are rather big :)
- tome 13y ago
  > There's an argument that mathematical functions are "back to front" and that it would be more natural to write functions left to right Totally agreed, but until programming languages adopt "x f = ..." for a definition of f then I'd prefer to stick to composing the traditional way round.

dons 13y ago

I strongly prefer the regular composition order. But I also use fclabels (FTW!) Changing the direction of composition makes no sense.

tel 13y ago
Composition order is the weirdest thing about Control.Lens.
dan00 13y ago
"Changing the direction of composition makes no sense." I also can't stand all these operators of the lens package. It feels like reading Perl code. The only annoying thing about all the other lens packages is the need for hiding '.' from Prelude.

boothead 13y ago

I thought that function composition (.) arises from the category instance for (->)? Actually on checking it seems that Prelude re-exports (.) from Data.Function. I'm sure I read somewhere that these had been unified, was I wrong?

tome 13y ago
I believe the argument against unifying is that you get very hard to decipher error messages.

crntaylor 13y ago

I also think it's a bit weird to flip direction of composition, but there are a couple of advantages -- 1. It keeps the "imperative" feel, so that you can write person.address.zipCode rather than zipCode.address.person 2. There's an argument that mathematical functions are "back to front" and that it would be more natural to write functions left to right, i.e. (x)f rather than f(x), so that the function composition f.g is "apply f then apply g" rather than "apply g then apply f" which is where we are at the moment.

tel 13y ago
Let's just go ahead and steal (<) and (>) for directional function composition everywhere. I'd rather just write `lt` and `gt`. x & f > g > h === h < g < f $ x
- tome 13y ago
  We already have (<<<) and (>>>) so you're nearly there :)
  - tel 13y ago
    Those always feel comical to use to me. It's like having a 747 landing strip to help guide a duck in for a safe landing.
    - tome 13y ago
      Yes they are rather big :)
tome 13y ago
> There's an argument that mathematical functions are "back to front" and that it would be more natural to write functions left to right Totally agreed, but until programming languages adopt "x f = ..." for a definition of f then I'd prefer to stick to composing the traditional way round.