From: Joel VanderWerf <vjoel@...>
Date: 2003-04-09T07:52:34+09:00
Subject: Re: The "!" and "?" characters.

Chris Pine wrote:
> ----- Original Message -----
> From: "Daniel Carrera" <dcarrera@math.umd.edu>
> 
> This is cool.  But it'd be cooler if I could write 'def !' and '5.!'.
> But 'def !' causes a parse error.
> 
> Now my question:
> Does anyone know why 'def !' causes a parse error?
> ----------------------------
> 
> Because it's interpreting `!' as `not', I think.  You can usually get around
> these problems by sending symbols, but `:!' gives a parse error.  You can
> usually get around *those* problems by interning a string:
> 
>   irb(main):001:0> class Integer
>   irb(main):002:1>   define_method ('!'.intern) {self *
> (self-1).send('!'.intern)}
>   irb(main):003:1> end
>   => #<Proc:0x400d3234@(irb):2>
>   irb(main):004:0> 5.send ('!'.intern)
>   Segmentation fault
> 
> Oops.
> 
> Hmmm...
> 
> Chris
> 

With a test for the self==1 case, it works...

class Integer
   define_method (:'!') do
     self == 1 ? 1 : self * (self-1).send(:'!')
   end
end

p(5.send(:'!')) # ==> 120

but I dont think there's any way to call #! except with #send, and that 
ain't pretty.