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Need to be able to default destructured values that are renamed. #6532

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B-Teague opened this issue Feb 22, 2024 · 2 comments · May be fixed by #6640
Open

Need to be able to default destructured values that are renamed. #6532

B-Teague opened this issue Feb 22, 2024 · 2 comments · May be fixed by #6640

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@B-Teague
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B-Teague commented Feb 22, 2024 •
edited

I came across a scenario where I needed to destructure multiple instances of a record: point1 and point2 that had an optional z coordinate for 3 dimensions. Please see example below

Point a : { x: Frac a, y: Frac a, z ? Frac a }

distanceBetweenPoints : Point a, Point a -> Frac a
distanceBetweenPoints = \point1, point2 ->
    { x: x1, y: y1, z: z1 ? 0.0 } = point1
    { x: x2, y: y2, z: z2 ? 0.0 } = point2
    Num.sqrt (
            Num.pow (x2 - x1) 2.0 +
            Num.pow (y2 - y1) 2.0 +
            Num.pow (z2 - z1) 2.0
    )
── RECORD PARSE PROBLEM in main.roc ────────────────────────────────────────────

I am partway through parsing a record, but I got stuck here:

14│      {x:x1, y:y1, z: z1 ? 0.0} = p1
@roboteng
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I was curious and looked into this a bit. It looks like the line { x: x1, y: y1, z ? 0.0 } = point1 can compile, but the line { x: x1, y: y1, z: z2 ? 0.0 } = point1 doesn't compile. It seems the root cause that you can't combine the optional record field with the renaming, both of which are needed here.

This was referenced Apr 7, 2024
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@roboteng
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Until this is solved, I found this workaround:

distanceBetweenPoints : Point a, Point a -> Frac a
distanceBetweenPoints = \point1, point2 ->
    { x: x1, y: y1, z: z1 } =
        { x, y, z ? 0.0 } = point1
        { x, y, z }

    { x: x2, y: y2, z: z2 } =
        { x, y, z ? 0.0 } = point2
        { x, y, z }

    Num.sqrt
        (
            Num.pow (x2 - x1) 2.0 +
            Num.pow (y2 - y1) 2.0 +
            Num.pow (z2 - z1) 2.0
        )

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Record parse roboteng/roc
Alias optional record field pattern roboteng/roc
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@roboteng @B-Teague