In fact never user *print-dup* when using edn to read back data
*print-dup* will output type and meta information that will not play well
with edn
user=> (binding [*print-dup* true] (pr-str (sorted-map :z 5 :a 1)))
"#=(clojure.lang.PersistentTreeMap/create {:a 1, :z 5})"
This "#=" with raise a RuntimeException because there is no dispatch on "="
in edn
Not using *print-dup* may lose some important information on data
user=> (binding [*print-dup* false] (pr-str (sorted-map :z 5 :a 1)))
"{:a 1, :z 5}" ;; this is a plain hash map
Just take care of providing your own custom tags to be able to read data
correctly
;; clumsy example
user=> (binding [*print-dup* false] (str "#treemap " (pr-str (sorted-map
:z 5 :a 1))))
"#treemap {:a 1, :z 5}"
You can then read it back with your custom reader
user=> (edn/read-string {:readers {'treemap #(merge (sorted-map) %)}}
(binding [*print-dup* false] (str "#treemap " (pr-str
(sorted-map :z 5 :a 1)))))
{:a 1, :z 5} ;; this is a sorted map
Seems like it should be possible to easily provide default printers and
readers for custom tags & data...
Cheers
Le mercredi 21 août 2013 22:38:18 UTC+2, kawas a écrit :
>
> Never had time to play with edn and custom readers but they are funny :)
>
> Use *print-dup* if you need to... just know how to custom read it :
>
> user=> (edn/read-string {:readers {'user.Foo map->Foo}} "#user.Foo{:a 1
> :b 2 :c 3}")
> #user.Foo{:a 1, :b 2, :c 3}
>
> user=> (edn/read-string {:readers {'user.Foo #(apply ->Foo %)}}
> "#user.Foo[1, 2, 3]")
> #user.Foo{:a 1, :b 2, :c 3}
>
> Nice
>
> Le mercredi 21 août 2013 22:33:00 UTC+2, kawas a écrit :
>>
>> By the way *print-dup* is the problem, maybe you should not use it :)
>>
>> Spot the difference :
>> user=> (binding [*print-dup* true] (prn (->Foo 1 2 3)))
>> #user.Foo[1, 2, 3]
>>
>> user=> (binding [*print-dup* false] (prn (->Foo 1 2 3)))
>> #user.Foo{:a 1, :b 2, :c 3}
>>
>> cheers
>>
>> Le mercredi 21 août 2013 19:55:59 UTC+2, Jim foo.bar a écrit :
>>>
>>> Hi everyone,
>>>
>>> I am trying to serialise a record with edn. I think I am using all the
>>> good practices but I get a weird error...I am using these simple functions:
>>>
>>> (defn data->string
>>> "Writes the object b on a file f on disk as a string."
>>> [b f]
>>> (io!
>>> (with-open [w (clojure.java.io/writer f)]
>>> (binding [*print-dup* true
>>> *out* w] (prn b)))))
>>>
>>> (defn string->data
>>> "Read the file f back on memory safely. Contents of f should be a
>>> clojure data-structure."
>>> [f]
>>> (io!
>>> (edn/read-string (slurp f))))
>>>
>>> and I am getting this error:
>>> *
>>> **RuntimeException No dispatch macro for: =
>>> clojure.lang.Util.runtimeException (Util.java:219)*
>>>
>>> Out of curiosity I tried something simpler like this:
>>>
>>> Clondie24.games.chess=> (defrecord FOO [a b c])
>>> Clondie24.games.chess.FOO
>>> Clondie24.games.chess=> (ut/data->string (FOO. :a :b :C) "FOO")
>>> nil
>>> Clondie24.games.chess=> (ut/string->data "FOO")
>>>
>>> RuntimeException No reader function for tag Clondie24.games.chess.FOO
>>> clojure.lang.EdnReader$TaggedReader.readTagged (EdnReader.java:739)
>>>
>>>
>>> What I am I missing? any suggestions?
>>>
>>> Jim
>>>
>>>
>>>
>>
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