David Tolpin wrote:
The same holds for XSLT. Most extensions to XSLT 1.0 compensate for deficiencies
of implementations which do not support efficient computation based on features
of XSLT.
I don't think so. There are plenty of extensions, in particular functions
dealing with string manipulation, regex or date/time/calendar related
functionality which are always faster if implemented natively in the
underlying programming language, regardless whether the XSLT processor
has some guearntees about optimizing certain constructs or not.
Not to mention the advantage of using the functions in XPath expressions.
I still think the division into XSLT for manipulating node trees and XPath
for navigation and manipulating primitive data like strings and dates is
a good one.
Therefore, determining required optimizations (and 'optimization' is a wrong
word -- computational
rules) and requiring conformant implementations to follow them would keep the
language simple
and easy to use.
The C/C++ and in particular the FORTRAN people did quite well without
any explicit guarantees about what the compiler will optimize. Although
everybody takes well-known techniques like constant folding, dead code
elimination, loop strength reduction, loop unrolling, jump optimization
and others for granted.
I can see why a lispisch/functional programming language requires the
run time environment to provide tail recursion elimination, firstly
because it's a reasonably simple and well established technology, and
because it encourages using recursive functions instead of writing
loops.
I don't see what other optimizations should be guaranteed, mainly
because stuff like handling lazy evaluation or chaching is *not* yet
well established in the sense that the algorithms providing the
optimizations guarantee that they always provide an advantage instead
of proving detrimental even in quite common cases. You don't want to
require a technique which is likely to slow down at least every tenth
program, according to the current level of wisdom.
J.Pietschmann
XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list