[Haskell-beginners] Reading JSON using Text.JSON

[Michael Xavier]

This isn't submitted as an answer to your question but having used Text.JSON
before in a project, for this one or maybe the next project you work on, you
might want to consider using Aeson. I find the API way nicer to work with
and it is apparently quite performant.

On Sun, May 15, 2011 at 12:51 PM, Adrien Haxaire
<adrien at adrienhaxaire.org>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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>



-- 
Michael Xavier
http://www.michaelxavier.net
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