Re: (real? (* +i +i)) -> #f

[JihemD <jihem01@online.fr>]

Ian Price wrote:
> 
> I believe guile only considers numbers with an _exact_ 0 imaginary part
> to be real. However, since all guile complex numbers are inexact, this
> means that (* +i +i) is not considered real.
> 
> scheme@(guile−user)> (* +i +i)
> $19 = −1.0+0.0i
> scheme@(guile−user)> (exact? (imag-part $19))
> $20 = #f
> 
> While I don't know if this was a specific concern when writing, this is
> in line with the interpretation in section 11.7.4  Numerical operations
> of the r6rs document.
> 
> http://www.r6rs.org/final/html/r6rs/r6rs-Z-H-14.html#node_sec_11.7.4.1
> 
> If x is a real number object, then (rational? x) is true if and only if
> there exist exact integer objects k1 and k2 such that (= x (/ k1 k2))
> and (= (numerator x) k1) and (= (denominator x) k2) are all true. Thus
> infinities and NaNs are not rational number objects.
> 
> (real? -2.5+0.0i)                              ⇒  #f
> (real? -2.5+0i)                                ⇒  #t
> 
> -- 
> Ian Price
> 

Thx Ian, the concept of exactness is new for me :
scheme@(guile-user)> (real? +0i)
$1 = #t
scheme@(guile-user)> (inexact->exact 1.0)
$2 = 1
scheme@(guile-user)> (inexact->exact (* +i +i))
$3 = -1
scheme@(guile-user)> (* +i +i)
$4 = -1.0+0.0i
scheme@(guile-user)> (real? (* +i +i))
$5 = #f
scheme@(guile-user)> (real? (inexact->exact (* +i +i)))
$6 = #t

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