Marcin 'Qrczak' Kowalczyk wrote:

Wed, 29 Aug 2001 16:34:52 +0200, Rijk-Jan van Haaften <rjchaaft@cs.uu.nl> pisze:

...

-3 ^ 2 = -9

In most programming languages as well as in mathematics it is quite unusual to have infix operators with a higher priority than prefix operators.

In mathematics the prefix negation is handled like in Haskell:

2 -3 = -9

I agree that many languages got it wrong :-)

This is not a simple matter. Mathematics (and some programming languages) also have postfix operators. Suppose ! is defined as usual as postfix factorial, and * as prefix square, then it is not obvious what the value of *5! should be. Mathematics has some conventions about operator precedence and associativity, but unfortunately not enough to serve as a model for programming languages which allow the definition of new operators. There seem to be two main classes of languages which allow prefix operators. Languages like C have them all at higher precedence than any infix operator, and right associative (in the sense that *$x is *($x), not (*$)x). This makes good sense for languages with many prefix operators. Suppose prefix * is bound to square, then *-5 is 25, and -*5 is -25. If instead you use the same precedence as the infix version of the operator, *-5 is illegal, and -*5 is -25. Haskell has only the one prefix operator. I remember there being a discussion about its precedence, but not the reasons for the final decision. If anyone remembers, it will be Joe Fasel. To my mind, it is not a big deal. Neither solution is ideal, but neither is a bad as not having unary -. Sure, that would simplify the syntax, but that is not necessarily the goal. --brian