`view` and UCM console output render reversed arguments for nested delayed computations

[rlmark]

The following expression

stream10 = Stream.range 0 10

In a watch expression and when viewed will render with the arguments reversed

 8 | > stream10
          ⧩
          _ -> Stream.range! 10 0

See slack thread from a Unison community member who found this

The problem is not unique to Stream or abilities. If you wrap a regular List.range function in the same way, you'll see the issue surface.

List.myRange n m _ = List.rangeClosed n m

> List.myRange 0 10

    6 | > List.myRange 0 10
          ⧩
          _ -> List.rangeClosed 10 0

[sergey-scherbina]

Actually, it seems to be not only a "rendering" issue but something more real with such partial application of terms. In my local instance of UCM, having these definitions in scratch file

use Nat +

stream10 = Stream.range 0 10
> stream10
> stream10 |> Stream.toList!
> Stream.map ((+)1) stream10 |> Stream.toList!

stream10' = 'let Stream.range! 0 10
> stream10'
> stream10' |> Stream.toList!
> Stream.map ((+)1) stream10' |> Stream.toList!

> Stream.range 0 10 |> Stream.map ((+)1) |> Stream.toList!

I've got when load it into UCM:

    4 | > stream10
          ⧩
          _ -> Stream.range! 10 0
  
    5 | > stream10 |> Stream.toList!
          ⧩
          []
  
    6 | > Stream.map ((+)1) stream10 |> Stream.toList!
          ⧩
          []
  
    9 | > stream10'
          ⧩
          '(Stream.range! 0 10)
  
    10 | > stream10' |> Stream.toList!
           ⧩
           [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  
    11 | > Stream.map ((+)1) stream10' |> Stream.toList!
           ⧩
           [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  
    13 | > Stream.range 0 10 |> Stream.map ((+)1) |> Stream.toList!
           ⧩
           [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Notice, please, that it actually returns an empty list with stream10 but works fine with stream10'.

Version of my UCM

$ ucm version
ucm version: release/M3 (built on 2022-03-08)

[pchiusano]

The weird runtime behavior is not present in trunk, but there is still an issue with decompilation flipping the order around.

finished evaluate in 0s (cpu), 0s (system)
Timing evaluate.respond...

    4 | > stream10
          ⧩
          _ -> Stream.range! 10 0
  
    5 | > stream10 |> Stream.toList!
          ⧩
          [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  
    6 | > Stream.map ((+)1) stream10 |> Stream.toList!
          ⧩
          [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  
    9 | > stream10'
          ⧩
          '(Stream.range! 0 10)
  
    10 | > stream10' |> Stream.toList!
           ⧩
           [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  
    11 | > Stream.map ((+)1) stream10' |> Stream.toList!
           ⧩
           [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  
    13 | > Stream.range 0 10 |> Stream.map ((+)1) |> Stream.toList!
           ⧩
           [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

[sergey-scherbina]

Have found a case where this issue affects evaluation in the latest build of UCM and base library:

> t1 _ = forever '(ask |> emit)
> Stream.pipe (Stream.range 0 10) t1 |> Stream.toList!
> stream10 = Stream.range 0 10
> Stream.pipe stream10 t1 |> Stream.toList!

what evaluates to:

    1 | > t1 _ = forever '(ask |> emit)
          ⧩
          let
            _float _eta = emit _eta
            _float1 = '(ask |> _float)
            '(forever _float)
  
    2 | > Stream.pipe (Stream.range 0 10) t1 |> Stream.toList!
          ⧩
          [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  
    3 | > stream10 = Stream.range 0 10
          ⧩
          _ -> Stream.range! 10 0
  
    4 | > Stream.pipe stream10 t1 |> Stream.toList!
          ⧩
          []

please note empty latest result also t1 displayed a bit broken

[dolio]

I think the erroneous output 4 in the last message was the same problem as #3166 and was fixed by #3266.

The decompiling problem is still around.