[Haskell-beginners] exception, not in IO

[Kees Bleijenberg]

The app I'am working on, converts a jsonString to another string encoding. 

The function I want to write is  jsonString -> (encoding, errorMsg)  so
String-> (String, String) 

For this purpose I have a typeable datastructure Glass. Because it is
typeable I can do (decodeJSON jsonString) :: Glass

But sometimes the jsonString is not valid (misformed or wrong fields).
decodeJSON then throws a exception.  I want to

catch that exection and transform the result to something like ("" ,
theErrorMsg). Unfortunately all catch functions want IO parameters. 

What can I do?

 

Kees

 

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