[Haskell-beginners] Reading JSON using Text.JSON

[Magnus Therning]

I wrote down some stuff from my first look at json, maybe it can
help you in getting further?

http://therning.org/magnus/archives/719

/M

On Sun, May 15, 2011 at 09:51:28PM +0200, Adrien Haxaire wrote:
> Hello,
> 
> I have this JSON string that I have put in a text file, test.json:
> 
> {"coordinates": [0.0, 1.0]}
> 
> using GHCi, I can read it like this:
> 
> > s <- readFile "test.json"
> > let r = decode s :: Result JSValue
> > r
> Ok (JSObject (JSONObject {fromJSObject = [("coordinates",JSArray
> [JSRational False (0 % 1),JSRational False (1 % 1)])]}))
> 
> I want to affect this array of two Double to the type Coordinates
> being defined like this:
> 
> type Coordinates = (Double, Double)
> 
> Using this type I can create a Node:
> 
> data Node = Node Coordinates Number
>           deriving (Eq, Ord, Show)
> 
> The problem is that I have no idea what to do with decoded JSValue.
> It seems I have to define an instance of JSON to read it. Does this
> mean using pattern matching to extract the values ?
> 
> What do I do with the Result type ? Should I get rid of it like this:
> 
> fromResult :: Result JSValue -> JSValue
> fromResult (Ok js) = js
> fromResult _ = JSNull
> 
> and work with the raw JValue ?
> 
> These questions might be trivial, but I know only imperative
> languages, which is why I like so much to learn Haskell and
> functional programming, lots to learn and discover :)
> 
> Many thanks in advance,
> Adrien
> 
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-- 
Magnus Therning                      OpenPGP: 0xAB4DFBA4 
email: magnus at therning.org   jabber: magnus at therning.org
twitter: magthe               http://therning.org/magnus


Perl is another example of filling a tiny, short-term need, and then
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     -- Alan Kay
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