[Haskell-cafe] Re: Unary Minus
DekuDekuplex at Yahoo.com
Mon Apr 6 07:02:58 EDT 2009
On Mon, 6 Apr 2009 12:13:09 +0200, Roel van Dijk
<vandijk.roel at gmail.com> wrote:
>On Mon, Apr 6, 2009 at 12:04 PM, Benjamin L.Russell
><DekuDekuplex at yahoo.com> 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.
What's interesting are the following definitions of the functions '-'
(binary minus) and "negate" given in "8 Standard Prelude" (see
>class (Eq a, Show a) => Num a where
> (+), (-), (*) :: a -> a -> a
> negate :: a -> a
> abs, signum :: a -> a
> fromInteger :: Integer -> a
> -- Minimal complete definition:
> -- All, except negate or (-)
> x - y = x + negate y
> negate x = 0 - x
The type of "negate," "a -> a", where a is a Num, is precisely what is
needed for a unary minus.
-- Benjamin L. Russell
Benjamin L. Russell / DekuDekuplex at Yahoo dot com
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