unary operators, precedence, grouping

["woger151" <woger151@xxxxxxxxxxxxxxxx>]

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))?