Parsing JSON Using F# (not Serialization)

Question

I am trying to build a tree (via a discriminated union type) in my F# application to represent my data generically. I researched what was available on the web and I have found things like the JavaScriptSerializer and the DataContractJsonSerializer. The problem is, I am not really serializing the data into a specific object.

Here is my discriminated union:

type ParameterTree =
    | End
    | Node of string * Dictionary<string, Parameter> * ParameterTree

I basically want to be able to read in from a stream and populate the ParameterTree with the data I am getting from the stream (including appropriate parent/child relationship). I am stuck on where to begin with this. If anybody can point me in the right direction, I would appreciate it.

Tomas Petricek · Accepted Answer · 2011-06-15 17:55:20Z

3

I think that the best option would be to use some more lightweight library that simply gives you the parsed key/value pairs in some .NET dictionary and then transform the data to a nice F# discriminated union.

The Json.NET library has a JObject.Parse method which seems to be doing exactly that. Here is a C# example from their web site:

JObject o = JObject.Parse(json);
string name = (string)o["Name"];
JArray sizes = (JArray)o["Sizes"];
string smallest = (string)sizes[0];

It shouldn't be too difficult to convert JObject and JArray structures to your union type.

answered Jun 15, 2011 at 17:55

Tomas Petricek

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1 Comment

JasCav Over a year ago

Hi @Tomas - I appreciate your answer (already accepted), but, I'm running into a minor problem. The reader I am creating is somewhat generic - the problem is defined by the user. Is there a way to iterate through the various properties and objects using your method (enumerate over them, generically)? I can't seem to find a way to do that. (I don't know what the fields will be beforehand - all I know is that it will be a tree structure).

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