Pattern Matching for tuples in `let` isn't work as expected

[astynax]

Hello!
This code works fine (in elm-0.17.1):

import Html exposing (text)

main =
  let
    b = a / 2
    a = 4  -- declarations are in mixed order, but it's fine!
  in text <| toString (a, b)

-- Output:
-- (4, 2)

but this one isn't

main =
  let
    (a, b) = (4, a / 2)
  in text <| toString (a, b)

-- Output:
-- (4, NaN)

There is no warning / compilation errors. And I think what this binding is legal as legal the former one.

Here is an example with strings:

main =
  let (a, b) = ("hello", String.append a " world!")
  in text <| toString (a, b)

-- Output:
-- ("hello", "undefined world!")

[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.

[astynax]

• Browser: Firefox 49.0
• OS: Ubuntu 16.04.1 LTS
• Elm version: 0.17.1 (installed from npm)

[astynax]

• Browser: Firefox 49.0
• OS: Ubuntu 16.04.1 LTS
• Elm version: 0.17.1 (installed from npm)

[evancz]

This is a duplicate of elm/compiler#873 which will be fixed in 0.18.

[evancz]

This is a duplicate of elm/compiler#873 which will be fixed in 0.18.