On 5/19/20 4:22 PM, Robert Haas wrote: > On Tue, May 19, 2020 at 9:51 AM Tom Lane <t...@sss.pgh.pa.us> wrote: >> Uh ... what exactly would be the point of that? The real reason to do >> this at all is not that we have it in for '!', but that we want to >> drop the possibility of postfix operators from the grammar altogether, >> which will remove a boatload of ambiguity. > > The ambiguity doesn't come from the mere existence of postfix > operators. It comes from the fact that, when we lex the input, we > can't tell whether a particular operator that we happen to encounter > is prefix, infix, or postfix. So hard-coding, for example, a rule that > '!' is always a postfix operator and anything else is never a postfix > operator is sufficient to solve the key problems. Then "SELECT a ! b" > can only be a postfix operator application followed by a column > labeling, a "SELECT a + b" can only be the application of an infix > operator.
So if I make a complex UDT where a NOT operator makes a lot of sense[*], why wouldn't I be allowed to make a prefix operator ! for it? All for what? That one person in the corner over there who doesn't want to rewrite their query to use factorial() instead? I'm -1 on keeping ! around as a hard-coded postfix operator. [*] I don't have a concrete example in mind, just this abstract one. -- Vik Fearing