Well first I was super intriguied by the example. But I agree with your conclusion, that statements should not also be expressions, so a = b = c shouldn't work

Well first I was super intriguied by the example. But I agree with your conclusion, that statements should not also be expressions, so a = b = c shouldn't work (at least not the way we're used to, that the b = c is an assignment "statement" that also produces an expression value). But in the end all this does is allow "a = b = c" to be a nonambiguous statement meaning, in more familiar notation, "a = b == c". Not exactly clear! So even though a language could use the same symbol for both assignment and equality-check, I don't recommend it! Although I still like to keep statements and expressions as strictly non-interchangeable constructs.