Mixing definterface and defprotocol - interface

Question

I try to implement interface representing arithmetic expressions. The interface will be used by java-side but the whole logic is on clojure.
Having:
(defprotocol ExtendsExpression
(toTree [this]))
(extend-type String
ExtendsExpression
(toTree [this] (symbol this)))
(extend-type Number
ExtendsExpression
(toTree [this] this))
(definterface Expression
(toTree []))
(defrecord Expression1 [^String oper arg]
Expression
(toTree [this]
(list (symbol oper) (toTree arg))))
(defrecord Expression2 [^String oper arg1 arg2]
Expression
(toTree [this]
(list (symbol oper) (toTree arg1) (toTree arg2))))
(defrecord Expression3 [^String oper arg1 arg2 arg3]
Expression
(toTree [this]
(list (symbol oper) (toTree arg1) (toTree arg2) (toTree arg3))))
I try to use it as:
(toTree (Expression3. "+" "a" "b" (Expression2. "*" "c" "d")))
but I'm getting:
IllegalArgumentException No implementation of method: :toTree of protocol: #'user/ExtendsExpression found for class: user.Expression3 clojure.core/-cache-protocol-fn (core_deftype.clj:541)
Why clojure tries to call toTree of ExtendsExpression for Expression3? I expect that for Expression3 it will call the toTree method of Expression interface.

Answer 1

Ok, Got it ;)
(defprotocol ExtendsExpression
(to-tree [this]))
(extend-type String
ExtendsExpression
(to-tree [this] (symbol this)))
(extend-type Number
ExtendsExpression
(to-tree [this] this))
(definterface Expression
(toTree []))
(defrecord Expression1 [^String oper arg]
ExtendsExpression
(to-tree [this]
(list (symbol oper) (to-tree arg)))
Expression
(toTree [this] (to-tree this)))
(defrecord Expression2 [^String oper arg1 arg2]
ExtendsExpression
(to-tree [this]
(list (symbol oper) (to-tree arg1) (to-tree arg2)))
Expression
(toTree [this] (to-tree this)))
(defrecord Expression3 [^String oper arg1 arg2 arg3]
ExtendsExpression
(to-tree [this]
(list (symbol oper) (to-tree arg1) (to-tree arg2) (to-tree arg3)))
Expression
(toTree [this] (to-tree this)))
(to-tree (Expression3. "+" "a" "b" (Expression2. "*" "c" "d"))) ;=> (+ a b (* c d))
and the records implements Expression interface, so I can call them from java easily:
(.toTree (Expression3. "+" "a" "b" (Expression2. "*" "c" "d"))) ;=> (+ a b (* c d))
just to check what interfaces Expression3 implements:
(-> Expression3 clojure.reflect/reflect :bases pprint)
#{clojure.lang.IHashEq java.io.Serializable clojure.lang.IKeywordLookup
clojure.lang.IPersistentMap clojure.lang.IRecord java.lang.Object
user.ExtendsExpression clojure.lang.IObj clojure.lang.ILookup
user.Expression java.util.Map}