I defined a function, count_nonnull, to return 1 if not null, 0 otherwise.
Then I defined a corresponding unary operator <~~. I wanted it for
expressions like <~~ item_1 + <~~ item_2. But because precedence of
user-defined ops is pretty low, I had to rewrite this as <~~(item_1) +
<~~(item_2), which is already no more efficient in use of parentheses than
count_nonnull.
Even worse, however, it turns out that _more_ parentheses were needed:
(<~~(item_1)) + (<~~(item_2)).
Why wouldn't <~~(item_1) + <~~(item_2) be parsed as (<~~(item_1)) +
(<~~(item_2))?
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