>What are meta data used for?
Its a open system it can be used for anything. If you have data about
your data that does not effect equality.
Examples:
The docstrings you can write in clojure are metadata.
(defn my-func
"my-func does XY"
[] "whatever")
This will be expanded to metadata like this: {:doc "my-func does XY"}
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The same goes for test.
The are metadata on functions: {:test (fn .....)}
--------------------------------------------------------------------------------------
An example that is used goes like this: if your mining data from the
net and other places you could that onto the data where you got it.
Example:
{:info "this is a good info"} could have the metadata {:source
www.whatever.com}
--------------------------------------------------------------------------------------
You could build a backup system where you tag your data with a
timestamp of the last backup.
--------------------------------------------------------------------------------------
>Are they similar to the reflective API in Java?
No, but you can use those from clojure too.
If you have to compair it to something in java I would say its
somewhat like annotations.
--------------------------------------------------------------------------------------
>Are they related to any FP theory?
No, not that I know of.
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