Re: [Haskell] HSXML version 1.13. Overloading polyvariadic functions

[mm]

On Sun, Feb 04, 2007 at 08:31:55PM -0800, [EMAIL PROTECTED] wrote:
 
 The benefit of representing XML-like documents as a typed data
 structure/Haskell code is static rejection of bad documents -- not
 only those with undeclared tags but also those where elements appear
 in wrong contexts.
 

Seems like 

http://www.informatik.uni-freiburg.de/~thiemann/haskell/WASH/

has has the same purpose, has it?

Cheers,

schneegloeckchen

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Re: [Haskell] HSXML version 1.13. Overloading polyvariadic functions

[oleg]

schneegloeckchen wrote:
 Seems like 
 http://www.informatik.uni-freiburg.de/~thiemann/haskell/WASH/
 has has the same purpose [as HSXML], has it?

_Some_ of the same purpose, yes. But HSXML does follow the
S-expression syntax -- something that has not been attained in
Haskell. Here's a sample HSXML:

  [p Haskell is a general purpose, 
   [[em [[strong purely]] functional]] programming language]

one may observe the absence of any commas and other list
delimiters. The things in square brackets can't be lists anyway
because their `elements' patently have different types. The strings
are represented as strings rather than (text string) etc. The `p'
element obviously can have arbitrary number of subelements and
strings.  On a Scheme system that takes square brackets (which is the
R6RS behavior) the above expression can be read with one `read' call
-- proving that HSXML is an S-expression.

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[Haskell] HSXML version 1.13. Overloading polyvariadic functions

[oleg]

This message announces the version 1.13 of HSXML. HSXML is a library
for writing and transforming typed semi-structured data in Haskell --
in S-expression syntax, with the extensible set of `tags', and
statically enforced content model restrictions. A particular
application is writing web pages in Haskell. We obtain HTML, XHTML or
other output formats by running the Haskell web page in an appropriate
rendering monad.

The benefit of representing XML-like documents as a typed data
structure/Haskell code is static rejection of bad documents -- not
only those with undeclared tags but also those where elements appear
in wrong contexts.

The web page
http://pobox.com/~oleg/ftp/Scheme/xml.html#typed-SXML
gives further motivation and description. It points to an example of
authoring web pages in HSXML and a complex example of
context-sensitive HSXLT transformations: producing structurally
distinct HTML and XML/RSS from the same master file.

The complete source code with several examples is available at
http://pobox.com/~oleg/ftp/Haskell/HSXML.tar.gz


The new version of HSXML contains more examples, many of which have
been very kindly suggested by shelarcy. One example in particular,
quote.hs, demonstrates overloading of a polyvariadic function. That
may seem impossible: a polyvariadic function typically has the type
forall t. C t = t. How overload on t? How to overload on arguments or
the result of the function if we don't know even the number of
arguments let alone their types. It's all in the future, when the
function is applied. As it turns out, if we make preparations in the
present, we can overload the future.
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