[Haskell-cafe] Haskell, successing crossplatform API standart
ok at cs.otago.ac.nz
Thu Dec 18 19:18:21 EST 2008
On 18 Dec 2008, at 7:41 pm, Belka wrote:
> Oh, but JSON doesn't seem to support tree-structured data...
Sure it does. In Haskell terms,
= JSON_Number Double -- not entirely clear, actually
| JSON_String String -- Unicode
| JSON_Array [JSON] -- order matters
| JSON_Object [(String,JSON)] -- Unicode keys, order no matter
It supports trees well enough that encoding XML as JSON is trivial.
To a first approximation,
= XML_CData String
| XML_Element String [(String,String)] [XML]
xml_to_json (XML_CData s) =
xml_to_json (XML_Elment name atts children) =
JSON_Object [("n", JSON_String name),
("a", JSON_Object [(k,JSON_STRING v) | (k,v) <-
("c", JSON_Array (map xml_to_json children))]
One can handle the other aspects of XML, I just couldn't be bothered.
Converting JSON that represents XML to XML is straightforward.
Of course the converse is true too.
json_to_xml (JSON_Number x) =
XML_Element "n"  XML_CData (show x)
json_to_xml (JSON_String s) =
XML_Element "s"  XML_CData s
json_to_xml (JSON_Array a) =
XML_Element "a"  map json_to_xml a
json_to_xml (JSON_Object o) =
XML_Element "o" 
[XML_Element "e" [("k",k)] (json_to_xml v) | (k,v) <- o]
Again, converting XML that represents JSON to JSON is straightward,
I just don't need to show it to make the point.
Also obviously, you might as well use Lisp s-expressions.
If you have a choice between XML and JSON, it may be worth remembering
that JSON is *far* easier to parse. I would expect a JSON parser to
be faster, and more importantly, I would expect it to be more reliable.
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