Re: RE: Declarative programming requires a different mindset
"Costello, Roger L." <firstname.lastname@example.org> writes: [about declarative programming] I enjoy your various posts with high level questions like this. I hope you will keep asking them. The question of what "the definition" of "declarative programming" is, is unanswerable, I think. People use words as tags to coordinate discussion of topics. A conversation often takes the form: Here is a phrase to use as a mnemonic: "..." Here are more phrases asserting the meaning of the mnemonic phrase. Here are more phrases that are meant as an invitiation for you to discuss a topic in terms of those phrases. In such a discussion you make a point by referencing the mnemonic phrase and redefining it. >> A clearer distinction is whether or not the program involves mutable state > variables. > > Since XSLT variables don't vary, are all XSLT programs declarative? > > Surely that's not the case. It's worthwhile to think of declarative programming as a style, in my opinion, and not all XSLT programs are written in a declarative style. A declarative programming language would be one that makes declarative programming easier than if it were not a declarative programming language. A program can have parts that are writte in a declarative style and parts that are not. I also think it is worthwhile to think of functional programming and declarative programing as different things. Perl is not a functional programming language, but you can write perl in a declarative style, e.g.: document(title(), body()); is written in a declarative style. You can also program in functional programming style using a procedural language. I suspect you could program in a "less functional" style using a functional programming language, but I can't think of an example. > Would someone give an example of XSLT code that is clearly imperative? This: <!-- given a matching author author --> <xsl:variable name="author" select="f:matching-author(.)"/> <!-- an author-link is the matching author's name and www address --> <author-link> <xsl:copy-of select="$author/name"/> <xsl:copy-of select="$author/www"/> </author-link> is more declarative and less imperative than: <!-- output an author-link start tag --> <xsl:text disable-output-escaping="yes"><author-link></xsl:text> <!-- get the matching author --> <xsl:variable name="author" select="f:matching-author(.)"/> <!-- output it's name --> <xsl:copy-of select="$author/name"/> <!-- output it's www address--> <xsl:copy-of select="$author/ww"/> <!-- output an author-link end tag --> <xsl:text disable-output-escaping="yes"></author-link></xsl:text> So, I think declarative programming is not a precisely definable concept. It refers to those parts of a programming style that you describe as being declarative. Kendall
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