#9 Multiple assignment operator in slist

[Dmitry Orlov]

'x ($y) =

reports "InvalidOperand: Nested lists and operators not
allowed"

but

('x 'y) ($y $x) =

does not complain, and probably corrupts memory. However,

('x 'y) {$y $x} =

works as it should, so this is strictly an omitted type
check.