`expect` not printing mentioned variables

[rtfeldman]

To reproduce, run this (either at the top level with roc test or inline with roc dev - both reproduce it):

x = 5
expect x != x
42

It prints a failed expectation, but doesn't show the value of x.

We should make a test case for this!

[witoldsz]

F# has a library for this: https://github.com/SwensenSoftware/unquote
It works in two ways:

• providing custom operators like =!, >!, etc., e.g. 5 >! 4 (meaning 5 should be greater than 4)
• or utilizing special expressions like <@ 5 > 2+2 @> (it evaluates the expression and in case of failure inspects and reduces the expression within)

[<Fact>]
let ``demo Unquote xUnit support`` () =
    test <@ [3; 2; 1; 0] |> List.map ((+) 1) = [1 + 3..1 + 0] @>

Test 'Module.demo Unquote xUnit support' failed: 

[3; 2; 1; 0] |> List.map ((+) 1) = [1 + 3..1 + 0]
[4; 3; 2; 1] = [4..1]
[4; 3; 2; 1] = []
false

So it does reduce the expression step by step.

I am not sure how this could map to Roc, but I thought it might be of interest to whoever tries to solve the issue.