Quotation unexpectedly creates cyclic structures

[yallop]

It's currently easy using quotation to inadvertently create a cyclic structure that fails when it's used. For example, the following code fails with a StackOverflowError on the call to show:

var e = '(1)
e = '(~e + 1)
e.show

@nicolasstucki tells me that this is likely to be fixed by the code in #5297, which makes the evaluation of quotations more eager.

[nicolasstucki]

The issue is with the current semantics the contents of the ~ are evaluated lazily and it is evaluated on the call to show. There the code is '(~e + 1) where it resolves the inner e as '(~e + 1) constructing '((~e + 1) + 1) and so on.

[nicolasstucki]

The simple workaround is to use a val instead.

[nicolasstucki]

I added a test to #5297 which confirms that this is fixed there.