Several questions about functional programming languages have got me thinking about whether XSLT is a functional programming language. If not, what features are missing? Has XSLT 2.0 shortened or closed the gap?
+3
A:
For the most part, what makes XSLT not a 100% functional programming language is it's inability to treat functions as a first-class data type.
There may be some others -- but that's the obvious answer.
Good luck!
Ian P
2008-09-21 02:23:46
+14
A:
XSLT is declarative as opposed to stateful.
Although XSLT is based on functional programming ideas, it is not a full functional programming language, it lacks the ability to treat functions as a first class data type. It has elements like lazy evaluation to reduce unneeded evaluation and also the absence of explicit loops.
Like a functional language though, I would think that it can be nicely parallelized with automatic safe multi threading across several processors.
From Wikipedia on XSLT:
As a language, XSLT is influenced by functional languages, and by text-based pattern matching languages like SNOBOL and awk. Its most direct predecessor was DSSSL, a language that performed the same function for SGML that XSLT performs for XML. XSLT can also be considered as a template processor.
Here is a great site on using XSLT as a functional language with the help of FXSL. FXSL is a library that implements support for higher-order functions.
Because of FXSL I don't think that XSLT has a need to be fully functional itself. Perhaps FXSL will be included as a W3C standard in the future, but I have no evidence of this.
Brian R. Bondy
2008-09-21 02:29:02
XSLT does have explicit loops: http://www.w3schools.com/xsl/el_for-each.asp
recursive
2010-09-03 14:09:42
fwiw this is also possible in .NET again through extension, and imho not as elegantly
annakata
2009-03-11 12:29:09
No extensions are necessary for functional programming in XSLT and Jeni knows this well: http://fxsl.sf.net . FXSL -- the Functional Programming Library for XSLT has been around for more than 8 years. It is written entirely in XSLT itself. Implements almost completely the Haskell Prelude functions.
Dimitre Novatchev
2009-04-08 16:20:31
+5
A:
That is sort of how it feels when I am programming it.
XSLT is entirely based on defining functions and applying them to selected events that come down the input stream.
XSLT lets you set a variable. Functional programming does not allow functions to have side effects - and that is a biggie.
Still, writing in XSLT, one has the same "feel as working in an FP fashion. You are working with input - you are not changing it - to create output.
This is a very, very different programming model from that used when working with the DOM API. DOM does not separate input and output at all. You are handed a data structure - and you mangle it how you see fit - without hesitation, restriction, or remorse.
Suffice it to say if you like FP and the principles behind it, you will probably feel comfortable working in it. Just like experience with event driven programming - and XML itself - will make you comfortable with it as well.
If your only experience is with top-down, non event driven programs - then XSLT will be very unfamiliar, alien landscape indeed. At least at first. Growing a little experience and then coming back to XSLT when XPath expressions and event-handling are really comfortable to you will pay off handsomely.
Hope this helps.
JohnnySoftware
2008-10-19 15:12:48
+2
A:
I am sure you guys have found this link by now :-) http://fxsl.sourceforge.net/articles/FuncProg/Functional%20Programming.html .
Well functions in XSLT are first class-citizens with some work arounds after all :-)