On Tue, 2004-04-06 at 11:15, Christophe TROESTLER wrote:

> Well I have a little question on this.  The guide says "Arithmetic
> operators: the same rules as in mathematics." but
> 
> -. 3.**2.
> 
> returns 9. while in math -x^2 means -(x^2) and not (-x)^2 !  I am
> curious why such an oddity.

The correct grammar here is rather nasty.
I use it in Felix, but i'm not at all sure it's
a good idea. The problem comes with:

	-x^2, x^-2, x^2^3

which are

	-(x^2), x^(-2), x^(2^3)

I use this grammar (which I hope delivers the above),
and is supposed to be the same as FORTRAN:
the nastiness is the 'uplink' from power to 
prefixed.

term:
  ...
  prefixed { $1 }

prefixed:
  | PLUS power  { apl $1 "pos" $2 }
  | MINUS power { apl $1 "neg" $2 }
  | TILDE power { apl $1 "compl" $2 }
  | power       { $1 }

/* exponentiation is right associative */
power:
  | superscript STARSTAR prefixed      { apl2 $2 "pow" [$1; $3] }
  | superscript { $1 }

superscript:
 ...

Knuth found this whole idea so distasteful that
in TeX the rule is that ^ and _ (super and subscript
operators) are unassociative and require explicit
bracketing.

Consider also:

	fgx
which usually means f(g(x)) but can also mean (fg)x ... 
I'm not sure there *are* any 'usual' rules in maths.

-- 
John Skaller, mailto:skaller@users.sf.net
voice: 061-2-9660-0850, 
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language http://felix.sf.net



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