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Dates are not comparable #1482

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rigdern opened this issue Sep 8, 2016 · 3 comments
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Dates are not comparable #1482

rigdern opened this issue Sep 8, 2016 · 3 comments

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@rigdern
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rigdern commented Sep 8, 2016

I tried sorting a list of Dates but got an error due to them not being comparable. Here's some code that produces this error:

import Html exposing (text)
import Date

dateList : List Date.Date
dateList =
  []

sortedDateList =
  List.sort dateList

main =
  text "Hello"

I expected this to compile but instead I got this compiler error:

Detected errors in 1 module.


-- TYPE MISMATCH ---------------------------------------------------------------

The argument to function `sort` is causing a mismatch.

10|   List.sort dateList
                ^^^^^^^^
Function `sort` is expecting the argument to be:

    List comparable

But it is:

    List Date.Date

Hint: Only ints, floats, chars, strings, lists, and tuples are comparable.

I'm using elm 0.17.1.
@process-bot
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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.

@JoeyEremondi
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JoeyEremondi commented Sep 8, 2016 •
edited
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You can use this comparison function with this sorting function.

That won't help you if you want to put them as keys in a Dict, though.

@evancz evancz mentioned this issue Sep 21, 2016
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@evancz
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evancz commented Sep 21, 2016

Added to meta issue #1008, thanks for the report!

@evancz evancz closed this as completed Sep 21, 2016
@jvoigtlaender jvoigtlaender mentioned this issue Apr 6, 2017
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4 participants
@rigdern @evancz @JoeyEremondi @process-bot