Beginner: Help with tasks: now : Task x Time

[Niklas Koponen]

Hi!

I'm trying to get the current time in elm but I can't figure out how use tasks. Now definition looks like this

now : Task x Time

The guide regarding tasks says:

Second, notice that the error type is the type variable x. When we saw Http.getString it had a concrete error type Http.Error. The Time.now task is different in that it will not fail in a special way. You will always get the time back. This type variable x is basically saying “I am not going to force you to handle a particular type of errors” because it does not produce any.

I have this message:

NewEntry Time

The problem is I don't know what to write for the error when I do Task.perform

Task.perform NewEntry [WHAT HERE?] Time.now

-Niklas

[Janis Voigtländer]

Since Time.now cannot fail (visible as per the type variable x), you can simply use http://package.elm-lang.org/packages/NoRedInk/elm-task-extra/2.0.0/Task-Extra#performFailproof, which relieves you from writing anything for the supposed fail case.

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[Niklas Koponen]

Thank you! That did the trick.

Took a look at the Task.Extra source and I have to admit it would have been impossible for me to come up with that solution.

-Niklas

[Janis Voigtländer]

That's why it is a provided function. :-)

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[Ian Mackenzie]

An alternate approach is just to use 'never' from elm-community/basics-extra directly for your '[WHAT HERE?]'. Although the error case actually comes first, so your example should be

Task.perform [WHAT HERE?] NewEntry Time.now

and my preferred answer would be (assuming 'import Basics.Extra exposing (never)')

Task.perform never NewEntry Time.now

It ends up being exactly the same thing under the hood - I just prefer this version because I find it very explicit, it's a little bit shorter, and most importantly it builds a nice solution out of little generic, modular pieces instead of using a more specialized function (if you can get used to how 'never' is used here, then you might be able to find uses for it elsewhere).