original.name="UnionType_Valid_8"
======
>>> main.whiley
type msgType1 is {int op, int[] payload}
type msgType2 is {int op, int[] rest, int header}

type msgType is msgType1 | msgType2

function f(msgType msg) -> int:
    if msg is msgType1:
        return msg.op
    else:
        return msg.op

public export method test() :
    assume f({op: 1, payload: [1, 2, 3]}) == 1

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