This question got stuck in mailman,

From: Kenneth Tilton ktilton@franz.com To: cl-json-devel@common-lisp.net Date: Wed, 19 May 2010 16:14:31 -0400 Subject: How to get a JS false from cl-json? t changes to unquoted true nicely, how about something that becomes false? I see there is a choice between null and false so we cannot just do false all the time.

nice lib, btw.

kt

And the answer is:

There are 3 different encoders. With the "streaming" encoder you have full control of the output. The guessing encoder (default) tries to make a decent json representation of a s-expression, it does not discriminate between null and false. The pretty new explicit encoder gives more control over the json representation, using a keyword in the first position of a list:

(test explicit-encoder (is (string= "true" (with-explicit-encoder (encode-json-to-string '(:true)))) "True") (is (string= "false" (with-explicit-encoder (encode-json-to-string '(:false)))) "False") (is (string= "null" (with-explicit-encoder (encode-json-to-string '(:null)))) "False")

There is a convenience function json-bool to make the keyword represenation:

(test json-bool (is (equal (json-bool t) '(:true))) (is (equal (json-bool 1) '(:true))) (is (equal (json-bool nil) '(:false))))

Also a related question is how to encode an empty list. As an empty json object {}, empty json-list [] or as json-null? That can also be handled with the explicit encoder. Here is a sample how a complex json structure can be built (from testencoder.lisp)

(sample-2-plists `(:object :method some-function :id 1 :params (:list (:json "{"id":"barId","name":"bar"}") (:true) (:list (:object "name" a :id b)) (:list (:object :name foo :id foo-id)) ))) (correct-json " {"method":"someFunction", "id":1,"params": [{"id":"barId","name":"bar"}, true, [{"name":"a","id":"b"}], [{"name":"foo","id":"fooId"}]]}")

/Henrik Hjelte