diff --git a/packages/core/array.js b/packages/core/array.js
new file mode 100644
index 0000000..b567689
--- /dev/null
+++ b/packages/core/array.js
@@ -0,0 +1,7 @@
+export function arrayUnique(array) {
+  return Array.from((new Set(array)).values());
+}
+
+export function flatten(array) {
+  return array.reduce((flattened, elm) => flattened.concat(elm), []);
+}
diff --git a/packages/core/fast-apply.js b/packages/core/fast-apply.js
index 0e42784..e69de29 100644
--- a/packages/core/fast-apply.js
+++ b/packages/core/fast-apply.js
@@ -1,23 +0,0 @@
-export function fastApply(holder, fn, args) {
-  if (holder || args.length > 5) {
-    return fn.apply(holder, args);
-  }
-  if (0 === args.length) {
-    return fn();
-  }
-  if (1 === args.length) {
-    return fn(args[0]);
-  }
-  if (2 === args.length) {
-    return fn(args[0], args[1]);
-  }
-  if (3 === args.length) {
-    return fn(args[0], args[1], args[2]);
-  }
-  if (4 === args.length) {
-    return fn(args[0], args[1], args[2], args[3]);
-  }
-  if (5 === args.length) {
-    return fn(args[0], args[1], args[2], args[3], args[4]);
-  }
-}
diff --git a/packages/core/function.js b/packages/core/function.js
new file mode 100644
index 0000000..35d9ac7
--- /dev/null
+++ b/packages/core/function.js
@@ -0,0 +1,35 @@
+export function compose(...funcs) {
+  if (funcs.length === 0) {
+    return arg => arg
+  }
+
+  if (funcs.length === 1) {
+    return funcs[0]
+  }
+
+  return funcs.reduce((a, b) => (...args) => a(b(...args)))
+}
+
+export function fastApply(holder, fn, args) {
+  if (holder || args.length > 5) {
+    return fn.apply(holder, args);
+  }
+  if (0 === args.length) {
+    return fn();
+  }
+  if (1 === args.length) {
+    return fn(args[0]);
+  }
+  if (2 === args.length) {
+    return fn(args[0], args[1]);
+  }
+  if (3 === args.length) {
+    return fn(args[0], args[1], args[2]);
+  }
+  if (4 === args.length) {
+    return fn(args[0], args[1], args[2], args[3]);
+  }
+  if (5 === args.length) {
+    return fn(args[0], args[1], args[2], args[3], args[4]);
+  }
+}
diff --git a/packages/core/index.js b/packages/core/index.js
index 4c5f159..4c7027a 100644
--- a/packages/core/index.js
+++ b/packages/core/index.js
@@ -9,108 +9,7 @@
  * (...args) => f(g(h(...args))).
  */
 
-export function arrayUnique(array) {
-  return Array.from((new Set(array)).values());
-}
-
-export function compose(...funcs) {
-  if (funcs.length === 0) {
-    return arg => arg
-  }
-
-  if (funcs.length === 1) {
-    return funcs[0]
-  }
-
-  return funcs.reduce((a, b) => (...args) => a(b(...args)))
-}
-
-export function flatten(array) {
-  return array.reduce((flattened, elm) => flattened.concat(elm), []);
-}
-
-export function virtualize(fields) {
-  return (Superclass) => {
-    class Virtualized extends Superclass {}
-    fields.forEach((field) => {
-      Virtualized.prototype[field] = function() {
-        const prototype = Object.getPrototypeOf(this);
-        const className = prototype.constructor.name;
-        throw new ReferenceError(
-          `"${className}" has undefined pure virtual method "${field}"`
-        );
-      }
-    });
-    return Virtualized;
-  }
-}
-
-export function virtualizeStatic(fields) {
-  return (Superclass) => {
-    class Virtualized extends Superclass {}
-    fields.forEach((field) => {
-      Virtualized[field] = function() {
-        const prototype = Virtualized.prototype;
-        const className = prototype.constructor.name;
-        throw new ReferenceError(
-          `"${className}" has undefined pure virtual static method "${field}"`
-        );
-      }
-    });
-    return Virtualized;
-  }
-}
-
-export class TickingPromise extends Promise {
-
-  constructor(executor, ticker) {
-    let _reject, _resolve;
-    super((resolve, reject) => {
-      _reject = reject;
-      _resolve = resolve;
-      if (executor) {
-        executor(resolve, reject);
-      }
-    });
-    this.executor = executor;
-    this.reject = _reject;
-    this.resolve = _resolve;
-    this.ticker = ticker;
-  }
-
-  static all(promises) {
-    const tickingPromises = [];
-    for (let i = 0; i < promises.length; i++) {
-      const promise = promises[i];
-      if (promise instanceof TickingPromise) {
-        tickingPromises.push(promise);
-        // After resolution, stop ticking the promise.
-        promise.then(() => {
-          tickingPromises.splice(tickingPromises.indexOf(promise), 1);
-        })
-      }
-    }
-    if (0 === tickingPromises.length) {
-      return super.all(promises);
-    }
-    return new TickingPromise(
-      (resolve) => {
-        resolve(Promise.all(promises));
-      },
-      (elapsed) => {
-        for (let i = 0; i < tickingPromises.length; i++) {
-          tickingPromises[i].tick(elapsed);
-        }
-      },
-    );
-  }
-
-  tick(elapsed) {
-    this.ticker(elapsed, this.resolve, this.reject);
-  }
-
-}
-
+export {arrayUnique, flatten} from './array';
 export {EventEmitterMixin as EventEmitter} from './event-emitter';
 export {merge} from './merge';
 export {
@@ -119,6 +18,8 @@ export {
   mergeDiffObject,
   mergeDiffPrimitive,
 } from './merge-diff';
-export {fastApply} from './fast-apply';
 export {inflate, deflate} from './flate';
+export {compose, fastApply} from './function';
 export {PropertyMixin as Property} from './property';
+export {TickingPromise} from './ticking-promise';
+export {virtualize, virtualizeStatic} from './virtualize';
diff --git a/packages/core/ticking-promise.js b/packages/core/ticking-promise.js
new file mode 100644
index 0000000..b2e0d46
--- /dev/null
+++ b/packages/core/ticking-promise.js
@@ -0,0 +1,49 @@
+export class TickingPromise extends Promise {
+
+  constructor(executor, ticker) {
+    let _reject, _resolve;
+    super((resolve, reject) => {
+      _reject = reject;
+      _resolve = resolve;
+      if (executor) {
+        executor(resolve, reject);
+      }
+    });
+    this.executor = executor;
+    this.reject = _reject;
+    this.resolve = _resolve;
+    this.ticker = ticker;
+  }
+
+  static all(promises) {
+    const tickingPromises = [];
+    for (let i = 0; i < promises.length; i++) {
+      const promise = promises[i];
+      if (promise instanceof TickingPromise) {
+        tickingPromises.push(promise);
+        // After resolution, stop ticking the promise.
+        promise.then(() => {
+          tickingPromises.splice(tickingPromises.indexOf(promise), 1);
+        })
+      }
+    }
+    if (0 === tickingPromises.length) {
+      return super.all(promises);
+    }
+    return new TickingPromise(
+      (resolve) => {
+        resolve(Promise.all(promises));
+      },
+      (elapsed) => {
+        for (let i = 0; i < tickingPromises.length; i++) {
+          tickingPromises[i].tick(elapsed);
+        }
+      },
+    );
+  }
+
+  tick(elapsed) {
+    this.ticker(elapsed, this.resolve, this.reject);
+  }
+
+}
diff --git a/packages/core/virtualize.js b/packages/core/virtualize.js
new file mode 100644
index 0000000..74a1627
--- /dev/null
+++ b/packages/core/virtualize.js
@@ -0,0 +1,31 @@
+export function virtualize(fields) {
+  return (Superclass) => {
+    class Virtualized extends Superclass {}
+    fields.forEach((field) => {
+      Virtualized.prototype[field] = function() {
+        const prototype = Object.getPrototypeOf(this);
+        const className = prototype.constructor.name;
+        throw new ReferenceError(
+          `"${className}" has undefined pure virtual method "${field}"`
+        );
+      }
+    });
+    return Virtualized;
+  }
+}
+
+export function virtualizeStatic(fields) {
+  return (Superclass) => {
+    class Virtualized extends Superclass {}
+    fields.forEach((field) => {
+      Virtualized[field] = function() {
+        const prototype = Virtualized.prototype;
+        const className = prototype.constructor.name;
+        throw new ReferenceError(
+          `"${className}" has undefined pure virtual static method "${field}"`
+        );
+      }
+    });
+    return Virtualized;
+  }
+}