On 5/18/05, David Carlisle <davidc(_at_)nag(_dot_)co(_dot_)uk> wrote:
I am accustomed to the lazy evaluation style of Haskell, where passing
parameters of infinite length is something natural,
like:
take 5 [1,2 ..]
takes the first 5 elements of the infinite list of natural numbers.
yes so in this case I was sugesting starting with [1,2 ..] then first
applying mapping a function from the natural numbers to strings that
writes the number as a unicode string by writing it using a using
unicode characters to represent the "digits" digits 0 to hex 10FFFF.
that gives you the (lazily constructed) sequence of all unicode strings.
Then filter that sequence using a function from string to boolean
that is true if the string is a valid xml file.
this could all be written in haskell.
Of course the algorithm is totally impractical although it could be made
more practical by having a more sensible sequence of initial strings.
even the impractical algorithm has some use though, it proves that the
sequence that you ask for does indeed exist.
I have never had a doubt of its existence -- it is obvious.
But let's be a little bit more practical -- even today one can convert
a DTD to a Haskell type, then use an existing Haskell test-generation
and automation tool, such as QuickCheck, then finally convert the
generated instances back to XML and use them for testing a given xslt
transformation.
For reference:
http://www.cafeconleche.org/#news2005May17
Cheers,
Dimitre
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