Hi,
I'm trying to learn how to make DSL in Clojure and Korma project is a
really good place to learn from. I'm trying this very simple stuff
(inspired by Korma, not Korma code):
(def predicates {'and :and
'or :or
'not :not
'> :gt
'< :lt
'= :eq})
(defn parse-where
[form]
(walk/postwalk-replace predicates form))
(defn condition->map [clause]
(apply hash-map (conj clause :op)))
(defn clauses->vec [clauses]
(reduce #(conj %1 (condition->map %2)) [ ] (rest clauses)))
(defn select* [ ]
{:type :select})
(defmacro select
[& body]
(make-query-then-execute #'select* body))
(defn- make-query-then-execute [fn-var body]
`(let [query-map# (-> (~fn-var) ~@body)]
query-map#))
(defn where-form [where-form* query form]
`(let [q# ~query]
(~where-form* q# (clauses->vec ~(parse-where `~form)))))
(defmacro where [query form]
(where-form #'where* query form))
(defn where* [query clause]
(update-in query [:where] conj clause))
But when I'm trying in the REPL:
(select
(where
(and (= :version 1.6) (= :name "Clojure"))
I'm getting:
ClassCastException java.lang.Character cannot be cast to
clojure.lang.IPersistentCollection clojure.core/conj (core.clj:83)
It is really hard to me to know what is going wrong. What is confusing me,
if I'm trying the where macro alone, it is working as excepted but when
integrating it with select macro, I got the exception.
I know it is not your problem but your help is greatly appreciated.
Thanks for help and time.
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