On Wed, Jul 16, 2008 at 12:12 PM, Yixin Cao <[EMAIL PROTECTED]> wrote: > > > On Wed, Jul 16, 2008 at 11:26 AM, Gabriel Dos Reis > <[EMAIL PROTECTED]> wrote: >> >> On Wed, Jul 16, 2008 at 10:25 AM, Ralf Hemmecke <[EMAIL PROTECTED]> wrote: >> > I think the whole discussion is misleading. >> > >> > A function has a source and target type. So, if there is >> > >> > /: (Integer, Integer) -> Fraction Integer >> > >> > than the return type is *always* Fraction(Integer), also for something >> > like 8/4 or 1/1. >> > >> > Why you see something else, is probably, because the interpreter adds >> > some conversions. That is mostly OK if you work as a user on the command >> > line, but in SPAD I would hate it since you would never know what type >> > you get if you apply a function like - or /. >> > >> > All I want to say is that here are some hidden coercions taking place so >> > the returned types are just what the interpreter is able to figure out. >> >> Yes, this is correct. >> In the interpreter, everytime you have a result of type Integer, and >> that integer >> is a constant that can be coerced into a tighter SubDomain of Integer, >> that is done. >> The behaviour is controlled by $useIntegerSubDomain. > > I knew the $useIntegerSubDomain. > > Is this unacceptable? > foo:(Integer,Integer)->Union(Integer,Fraction Integer) > foo(nn,dd) == > f := nn / dd > denom f = 1 => numer f > f
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