[Haskell-cafe] Re: Unary Minus

On Mon, 6 Apr 2009 12:13:09 +0200, Roel van Dijk wrote:

On Mon, Apr 6, 2009 at 12:04 PM, Benjamin L.Russell wrote:

...

Interesting. ?How is this hack implemented?

This seems to be the relevant grammar: lexp6 -> - exp7 lpat6 -> - (integer | float) (negative literal)

The '6's and the '7' are superscripts. Perhaps the hack is in the precedence of the expression in which an unary minus is allowed.

Yes, I see it now. It's under "9.5 Context-Free Syntax," instead of being under "9.2 Lexical Syntax," so it's a syntactic rule, rather than a lexical rule. According to the rule, "a left-expression of precedence level 6" consists of "'-' followed by an expression of precedence level 7", and "a left-pattern of precedence level 6" consists of "'-' followed by (an integer or a float)", and by definition, this is a "negative literal." Integers and floats, in turn, are part of the lexical syntax. -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^