On Wed, 2012-12-12 at 12:39 +0800, Daniel Hartwig wrote: > On 12 December 2012 11:21, Nala Ginrut <nalagin...@gmail.com> wrote: > > It's weird to see that: > > (exact? 'a) > > ================err msg=============== > > ERROR: In procedure exact?: > > ERROR: In procedure exact?: Wrong type argument in position 1: a > > ==================end================= > > > > And I have to do this: > > (define (fraction? obj) > > (and (number? obj) (inexact? obj))) > > “Fraction” is not a very precise term or relevent to the type > hierarchy in Scheme, please do not use that. Disregard that GOOPS > define such a class, the more precise term is “rational” for which > there is already a predicate.
Many thanks! But rational? returns TRUE both 1.5 & 1/2, I need a predicate to check between 'float' and 'fraction' distinctly. Are you suggesting I use (is-a? obj <fraction>) for 'fraction?' ? > > Your fraction? predicate is not equivalent to the GOOPS <fraction> > class, which are exact? and (in all cases I believe) also rational?. > > > > > > > Why not 'exact?' and 'inexact?' doesn't check 'number?' first? > > Performance. They are intended to be used in numerical paths and > requiring them to check first number? every time is very inefficient. > You will note that they are documented as “exact? Z“ rather than > “exact? obj”.
