unexpected output when updating field name

[shriram]

I was not expecting this last line of REPL output (this is on pyret-dev):

> data Foo: f(a, b) end
> f(2, 3)
f(23)
> f(2, 3).{a: 4}
{a4b3$fieldNames[raw-array: "a""b"]_match<method:f>}

[shriram]

Note: the actual output looks a bit different, but copying-and-pasting REPL output still does not work (per a previously filed report, and that's a serious one).

[jpolitz]

See #307. This should be an error, but has a more complicated story long-term.

[jswrenn]

This is a surprising output:

> data Foo: f(a, b) end
> f(2,3).{c:4}
{c: 4, a: 2, b: 3, $fieldNames: [raw-array: "a", "b"], _match: <method:f>}