Subject: RE: [xsl] () equivalent to () ? From: "Michael Kay" <mike@xxxxxxxxxxxx> Date: Mon, 22 Aug 2005 14:48:42 +0100 |
> Is the empty sequence equal to itself? Define "equal". The "=" operator returns false, the "eq" operator returns (), the deep-equals() function returns true, the "is" operator returns (). > > I would say yes, because what charactarizes the empty > sequence, its length and > its members(AFAICT), is always the same. IIRC, the empty > sequence is a > constant value and hence it must by common principles be > identical to itself. Sequences don't have identity; and there's more than one possible definition of equality. > As a consequence, the expression "data( () )" should be > equivalent to its > argument, "()", the empty sequence. Be careful with words: you've drifted from "equal" to "identical" to "equivalent". It's true that the result of data(()) is (). However, systems are allowed to do static type checking. The static types inferred for () and data(()) are different. So there's at least one sense in which they are not equivalent. > > However, testing this theory in practice in a host language > such as XSLT 2.0 > is impossible(?) since all comparison operators returns the > empty sequence > when an operand is the empty sequence. You're talking about a new comparison operation of your own invention which you haven't fully defined, and which seems to differ slightly from those already defined in the language. You're welcome to do this. First you need to define what you want its semantics to be, and then you can implement it as a function. But so far, you haven't defined its semantics except by appeal to "common principles" - which you will quickly find are not as common as you thought. Michael Kay http://www.saxonica.com/
Current Thread |
---|
|
<- Previous | Index | Next -> |
---|---|---|
Re: [xsl] () equivalent to () ?, Frans Englich | Thread | Re: [xsl] () equivalent to () ?, Frans Englich |
RE: [xsl] Converting to ASCII equiv, Michael Kay | Date | Re: [xsl] alphabetic set of xsl:res, James Cummings |
Month |