Curious why foldl in haskell has a different type than elm.

[MrRacoon]

In elm (5.0.0):

foldl : (a -> b -> b) -> b -> List a -> b
foldr : (a -> b -> b) -> b -> List a -> b

In haskell:

foldl :: Foldable t => (b -> a -> b) -> b -> t a -> b
foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b

notice the arguments of the function given to foldl seem to be backwards. Is that intended?

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[MrRacoon]

oh interesting, just saw this: elm/compiler#346

[MrRacoon]

oh interesting, just saw this: elm/compiler#346

[evancz]

Yep, that's the reasoning! This way you can write functions such that "The data structure is always last" and it works nice with folds. The direction of your fold shouldn't require a refactor IMO.

[evancz]

Yep, that's the reasoning! This way you can write functions such that "The data structure is always last" and it works nice with folds. The direction of your fold shouldn't require a refactor IMO.

[MrRacoon]

Does this image still apply to elm? (its from a haskell deck. I use this image to teach people the difference between the folds)

[MrRacoon]

Does this image still apply to elm? (its from a haskell deck. I use this image to teach people the difference between the folds)

[evancz]

I think it'd be better to talk about this more on the Slack or on elm-discuss.

[evancz]

I think it'd be better to talk about this more on the Slack or on elm-discuss.

[MrRacoon]

Aye!

[MrRacoon]

Aye!