> On Dec 3, 2007 8:05 AM, Ken Bloom <kbl...@gmail.com> wrote:

> > On Sun, 02 Dec 2007 22:23:23 -0500, Eric Mahurin wrote:

> > > Note:  parts of this message were removed by the gateway to make it a
> > > legal Usenet post.

> > > On Nov 30, 2007 7:28 AM, Ruby Quiz <ja...@grayproductions.net> wrote:

> > >> For an added bonus, try to keep the parentheses added to infix
> > >> expressions to
> > >> the minimum of what is needed.

> > > My solution does the above, plus a few more things:

> > > * maintains an OO data structure (to do everything below) * further
> > > reduce parentheses (and post-fix stack depth) by using some
> > > associativity
> > > * evaluates the result
> > > * gives stack-reduced post-fix form

> > > The basic idea of the solution is to have an object for each expression
> > > (possibly with sub-expressions as operands) and have methods for
> > > applying another operation in either direction (i.e. have both #add and
> > > #radd - reverse add).  This allows independent decisions on what each
> > > type of expression should do when it is in either operand of another
> > > operation.

> > > Here are a few examples (result shows internal postfix, infix, and
> > > result):

> > >>ruby quiz148.rb "2 3 5 + *"
> > > 2 3 5 + * => 2*(3 + 5) =>  16
> > >>ruby quiz148.rb "56 34 213.7 + * 678 -"
> > > 56 34 213.7 + * 678 - => 56*(34 + 213.7) - 678 =>  13193.2
> > >>ruby quiz148.rb "1 56 35 + 16 9 - / +"
> > > 1 56 35 + 16 9 - / + => 1 + (56 + 35)*(16 - 9) =>  14
> > >>ruby quiz148.rb "1 2 3 4 5 + + + +"
> > > 1 2 + 3 + 4 + 5 + => 1 + 2 + 3 + 4 + 5 =>  15
> > >>ruby quiz148.rb "1 2 3 4 5 - - - -"
> > > 1 2 - 3 + 4 - 5 + => 1 - 2 + 3 - 4 + 5 =>  3

> > This doesn't look right.
> > 3 5 * 5 8 * / => 3*5*(5*8) =>  0

> > Thanks Ken,

> I obviously didn't test divide.  My previously solution has a stupid typo in
> Quotient#to_s.  Should be:

> class Quotient < Product
>   def to_s
>     "#{@left}/#{@right}"  # had a * operator here before, whoops!
>   end
>   ...

> Here's a couple more tests:

> >ruby quiz148.rb "3 5 / 5 8 / /"
> 3 5 / 5 / 8 * => 3/5/5*8 =>  0
> >ruby quiz148.rb "3 5 5 8 / / /"
> 3 5 5 / 8 * / => 3/(5/5*8) =>  0

> All the results are zero because it is using ruby's Fixnum#/.  The last form
> isn't quite optimal because it preferring to minimize divisions over
> minimizing groupings/stack-depth.  If you use the commented code in
> Product#rdiv like this:

>   def rdiv(other)
>     # could do this to reduce grouping and stack depth
>     # but this will increase expensive divisions
>     @left.rdiv(other).div(@right) # might have more divisions now
>     #other.div(Group.new(self))
>   end

> you'll get this:

> >ruby quiz148.rb "3 5 5 8 / / /"

> 3 5 / 5 * 8 / => 3/5*5/8 =>  0