diff --git a/README.adoc b/README.adoc
index 309489a..a469e17 100644
--- a/README.adoc
+++ b/README.adoc
@@ -33,7 +33,7 @@ A proof of concept for simple template engine using threading macros.
 
 == License
 
-Copyright © 2022-2023 https://scrapbox.io/uochan/uochan[Masashi Iizuka]
+Copyright © 2022-2024 https://scrapbox.io/uochan/uochan[Masashi Iizuka]
 
 This program and the accompanying materials are made available under the
 terms of the Eclipse Public License 2.0 which is available at
diff --git a/bb_test_runner.clj b/bb_test_runner.clj
index 11223df..f4156e1 100644
--- a/bb_test_runner.clj
+++ b/bb_test_runner.clj
@@ -1,6 +1,13 @@
 (ns bb-test-runner
   (:require
    [clojure.test :as t]
-   [mint.core-test]))
+   [mint.core-test]
+   [mint.evaluator-test]
+   [mint.evaluator.condition-test]
+   [mint.evaluator.threading-test]))
 
-(t/run-tests 'mint.core-test)
+(t/run-tests
+ 'mint.core-test
+ 'mint.evaluator-test
+ 'mint.evaluator.condition-test
+ 'mint.evaluator.threading-test)
diff --git a/src/mint/constant.cljc b/src/mint/constant.cljc
new file mode 100644
index 0000000..be334ed
--- /dev/null
+++ b/src/mint/constant.cljc
@@ -0,0 +1,4 @@
+(ns mint.constant)
+
+(def start-delm "{{")
+(def end-delm "}}")
diff --git a/src/mint/core.cljc b/src/mint/core.cljc
index 4024217..05ea1f9 100644
--- a/src/mint/core.cljc
+++ b/src/mint/core.cljc
@@ -1,90 +1,12 @@
 (ns mint.core
   (:require
-   [clojure.string :as str]))
-
-(def ^:private start-delm "{{->")
-(def ^:private end-delm "}}")
-(def ^:private end-delm-count (count end-delm))
-
-(defmulti eval*
-  (fn [form _data]
-    (when (sequential? form)
-      (first form))))
-
-(defmethod eval* :default
-  [form data]
-  (let [seq-form? (sequential? form)
-        sym-form? (symbol? form)]
-    (cond
-      (and (not seq-form?)
-           (not sym-form?))
-      form
-
-      (not seq-form?)
-      (get data (keyword form))
-
-      :else
-      (when-let [f (get data (keyword (first form)))]
-        (->> (rest form)
-             (seq)
-             (map #(eval* % data))
-             (apply f))))))
-
-(defmethod eval* '->
-  [[_ v & forms] data]
-  (when-let [x (eval* v data)]
-    (reduce (fn [accm form]
-              (let [[head & args] (if (sequential? form) form [form])
-                    form' (concat (list head accm) args)]
-                (eval* form' data)))
-            x forms)))
-
-(defmethod eval* '->>
-  [[_ v & forms] data]
-  (when-let [x (eval* v data)]
-    (reduce (fn [accm form]
-              (let [form' (concat (if (sequential? form) form [form])
-                                  [accm])]
-                (eval* form' data)))
-            x forms)))
-
-(defn- parse-pre
-  [s]
-  (if-let [idx (str/index-of s start-delm)]
-    [(subs s 0 idx) (subs s idx)]
-    [s nil]))
-
-(defn- parse-post
-  [s]
-  (if-let [idx (str/index-of s end-delm)]
-    [(subs s 0 (+ idx end-delm-count)) (subs s (+ idx end-delm-count))]
-    [nil s]))
-
-(defn- parse
-  [s]
-  (let [[pre tmp] (parse-pre s)
-        [body post] (when tmp (parse-post tmp))]
-    [pre body post]))
-
-(defn- eval-body
-  [body data]
-  (let [form-str (-> body
-                     (str/replace start-delm "(->")
-                     (str/replace end-delm ")"))]
-    (try
-      (-> form-str
-          (read-string)
-          (eval* data)
-          (str))
-      (catch #?(:clj Exception :cljs js/Error) ex
-        (throw (ex-info "Invalid form" {:form form-str
-                                        :message (ex-message ex)}))))))
+   [mint.evaluator :as evaluator]
+   [mint.evaluator.condition]
+   [mint.evaluator.threading]
+   [mint.parser :as parser]))
 
 (defn render
-  [s data]
-  (loop [content s
-         res []]
-    (let [[pre body post] (parse content)]
-      (if (and body post)
-        (recur post (conj res pre (eval-body body data)))
-        (str/join "" (conj res pre))))))
+  [template-str data]
+  (-> template-str
+      (parser/parse)
+      (evaluator/evaluate data)))
diff --git a/src/mint/evaluator.cljc b/src/mint/evaluator.cljc
new file mode 100644
index 0000000..6fbe46d
--- /dev/null
+++ b/src/mint/evaluator.cljc
@@ -0,0 +1,46 @@
+(ns mint.evaluator
+  (:require
+   [clojure.string :as str]
+   [mint.constant :as const]))
+
+(defmulti eval*
+  (fn [sexp _data]
+    (if (sequential? sexp)
+      (first sexp)
+      sexp)))
+
+(defmethod eval* :default
+  [form data]
+  (let [[first-item :as form] (if (sequential? form) form [form])
+        form-count (count form)]
+    (cond
+      (and (= 1 form-count)
+           (not (symbol? first-item)))
+      first-item
+
+      (= 1 form-count)
+      (get data (keyword first-item))
+
+      :else
+      (let [f (get data (keyword first-item))]
+        (when (fn? f)
+          (some->> (rest form)
+                   (seq)
+                   (map #(eval* % data))
+                   (apply f)))))))
+
+(defn- evaluate*
+  [expression-str data]
+  (-> expression-str
+      (str/replace const/start-delm "(")
+      (str/replace const/end-delm ")")
+      (read-string)
+      (eval* data)))
+
+(defn evaluate
+  [parsed data]
+  (->> parsed
+       (map #(if (= :expression (first %))
+               (evaluate* (second %) data)
+               (second %)))
+       (str/join "")))
diff --git a/src/mint/evaluator/condition.cljc b/src/mint/evaluator/condition.cljc
new file mode 100644
index 0000000..550f8f5
--- /dev/null
+++ b/src/mint/evaluator/condition.cljc
@@ -0,0 +1,8 @@
+(ns mint.evaluator.condition
+  (:require
+   [mint.evaluator :as evaluator]))
+
+(defmethod evaluator/eval* 'when
+  [[_ v & forms] data]
+  (when (evaluator/eval* v data)
+    (evaluator/eval* (last forms) data)))
diff --git a/src/mint/evaluator/threading.cljc b/src/mint/evaluator/threading.cljc
new file mode 100644
index 0000000..562e610
--- /dev/null
+++ b/src/mint/evaluator/threading.cljc
@@ -0,0 +1,23 @@
+(ns mint.evaluator.threading
+  (:require
+   [mint.evaluator :as evaluator]))
+
+(defmethod evaluator/eval* '->
+  [[_ v & forms] data]
+  (reduce
+   (fn [accm form]
+     (let [[head & rest-form] (if (sequential? form) form [form])
+           form' (concat (list head accm) rest-form)]
+       (evaluator/eval* form' data)))
+   (evaluator/eval* v data)
+   forms))
+
+(defmethod evaluator/eval* '->>
+  [[_ v & forms] data]
+  (reduce
+   (fn [accm form]
+     (let [form' (concat (if (sequential? form) form [form])
+                         [accm])]
+       (evaluator/eval* form' data)))
+   (evaluator/eval* v data)
+   forms))
diff --git a/src/mint/parser.cljc b/src/mint/parser.cljc
new file mode 100644
index 0000000..3ef38c7
--- /dev/null
+++ b/src/mint/parser.cljc
@@ -0,0 +1,29 @@
+(ns mint.parser
+  (:require
+   [clojure.string :as str]
+   [mint.constant :as const]))
+
+(defn- parse*
+  [template-str]
+  (let [start-idx (str/index-of template-str const/start-delm)
+        end-idx (and start-idx
+                     (str/index-of template-str const/end-delm (inc start-idx)))]
+    (if (and start-idx end-idx)
+      (let [end-idx' (+ end-idx (count const/end-delm))
+            pre (subs template-str 0 start-idx)
+            body (subs template-str start-idx end-idx')
+            post (subs template-str end-idx')]
+        [[:string pre]
+         [:expression body]
+         [:string post]])
+      [[:string template-str]])))
+
+(defn parse
+  [template-str]
+  (->> (loop [result []
+              template-str template-str]
+         (let [[pre body post :as parsed] (parse* template-str)]
+           (if (seq post)
+             (recur (concat result [pre body]) (second post))
+             (concat result parsed))))
+       (remove #(= % [:string ""]))))
diff --git a/test/mint/core_test.cljc b/test/mint/core_test.cljc
index 95a8889..52f6e18 100644
--- a/test/mint/core_test.cljc
+++ b/test/mint/core_test.cljc
@@ -10,24 +10,6 @@
    :clj (t/deftest README-test
           (t/is (testdoc (slurp (io/file "README.adoc"))))))
 
-(t/deftest eval*-test
-  (t/is (= 10 (sut/eval* 'foo {:foo 10})))
-  (t/is (= 10 (sut/eval* '(inc 9) {:inc inc})))
-  (t/is (= 10 (sut/eval* '(inc (inc 8)) {:inc inc})))
-
-  (t/testing "thread first"
-    (t/is (= 10 (sut/eval* '(-> 9 inc) {:inc inc})))
-    (t/is (= 10 (sut/eval* '(-> foo (- 1)) {:foo 11, :- -})))
-    (t/is (= 10 (sut/eval* '(-> (inc foo) (- 1)) {:foo 10, :- -, :inc inc}))))
-
-  (t/testing "thread last"
-    (t/is (= 10 (sut/eval* '(->> 9 inc) {:inc inc})))
-    (t/is (= 10 (sut/eval* '(->> foo (- 11)) {:foo 1, :- -})))
-    (t/is (= 10 (sut/eval* '(->> (inc foo) (- 11)) {:foo 0, :- -, :inc inc}))))
-
-  (t/testing "qualified keyword"
-    (t/is (= 10 (sut/eval* '(->> foo/bar) {:foo/bar 10})))))
-
 (t/deftest render-test
   (t/is (= "" (sut/render "" {})))
   (t/is (= "foo" (sut/render "foo" {})))
diff --git a/test/mint/evaluator/condition_test.cljc b/test/mint/evaluator/condition_test.cljc
new file mode 100644
index 0000000..6541ec0
--- /dev/null
+++ b/test/mint/evaluator/condition_test.cljc
@@ -0,0 +1,14 @@
+(ns mint.evaluator.condition-test
+  (:require
+   [clojure.test :as t]
+   [mint.evaluator :as sut]
+   [mint.evaluator.condition]))
+
+(t/deftest eval*-condition-test
+  (t/testing "when"
+    (t/is (= "hello" (sut/eval* '(when foo "hello") {:foo 10})))
+    (t/is (= "10hello" (sut/eval* '(when foo (str foo "hello")) {:foo 10
+                                                                 :str str})))
+    (t/is (nil? (sut/eval* '(when foo "hello") {:foo nil})))
+    (t/is (nil? (sut/eval* '(when foo "hello") {:foo false})))
+    (t/is (nil? (sut/eval* '(when foo "hello") {})))))
diff --git a/test/mint/evaluator/threading_test.cljc b/test/mint/evaluator/threading_test.cljc
new file mode 100644
index 0000000..d723d70
--- /dev/null
+++ b/test/mint/evaluator/threading_test.cljc
@@ -0,0 +1,16 @@
+(ns mint.evaluator.threading-test
+  (:require
+   [clojure.test :as t]
+   [mint.evaluator :as sut]
+   [mint.evaluator.threading]))
+
+(t/deftest eval*-threading-test
+  (t/testing "thread first"
+    (t/is (= 10 (sut/eval* '(-> 9 inc) {:inc inc})))
+    (t/is (= 10 (sut/eval* '(-> foo (- 1)) {:foo 11, :- -})))
+    (t/is (= 10 (sut/eval* '(-> (inc foo) (- 1)) {:foo 10, :- -, :inc inc}))))
+
+  (t/testing "thread last"
+    (t/is (= 10 (sut/eval* '(->> 9 inc) {:inc inc})))
+    (t/is (= 10 (sut/eval* '(->> foo (- 11)) {:foo 1, :- -})))
+    (t/is (= 10 (sut/eval* '(->> (inc foo) (- 11)) {:foo 0, :- -, :inc inc})))))
diff --git a/test/mint/evaluator_test.cljc b/test/mint/evaluator_test.cljc
new file mode 100644
index 0000000..7d8b0b9
--- /dev/null
+++ b/test/mint/evaluator_test.cljc
@@ -0,0 +1,44 @@
+(ns mint.evaluator-test
+  (:require
+   [clojure.test :as t]
+   [mint.evaluator :as sut]))
+
+(t/deftest eval*-default-test
+  (t/testing "replace value"
+    (t/is (= 10 (sut/eval* 'foo {:foo 10}))))
+
+  (t/testing "eval function"
+    (t/is (= 10 (sut/eval* '(inc 9) {:inc inc})))
+    (t/is (= 10 (sut/eval* '(inc (inc 8)) {:inc inc}))))
+
+  (t/testing "qualified keyword"
+    (t/is (= 10 (sut/eval* '(->> foo/bar) {:foo/bar 10}))))
+
+  (t/testing "unknown value"
+    (t/is (nil? (sut/eval* 'unknown {}))))
+
+  (t/testing "unknown function"
+    (t/is (nil? (sut/eval* '(unknown 1) {})))))
+
+(t/deftest evaluate-test
+  (t/is (= "" (sut/evaluate [] {})))
+
+  (t/testing "string"
+    (t/is (= "foo"
+             (sut/evaluate [[:string "foo"]] {}))))
+
+  (t/testing "expression"
+    (t/is (= "bar"
+             (sut/evaluate [[:expression "{{foo}}"]]
+                           {:foo "bar"})))
+    (t/is (= "bar"
+             (sut/evaluate [[:expression "{{f}}"]
+                            [:expression "{{oo}}"]]
+                           {:f "b" :oo "ar"}))))
+
+  (t/testing "string and expression"
+    (t/is (= "hello world!"
+             (sut/evaluate [[:string "hello "]
+                            [:expression "{{foo}}"]
+                            [:string "!"]]
+                           {:foo "world"})))))