From 3f0d47355b91597eceab01da9da9abcd69ed9a46 Mon Sep 17 00:00:00 2001
From: Andy Edwards <jedwards@fastmail.com>
Date: Mon, 30 Nov 2020 20:44:44 -0600
Subject: [PATCH] feat: add flow defs [WIP]

---
 .flowconfig                                 |   11 +
 package.json                                |    1 +
 src/Validation.js.flow                      |   29 +
 src/errorReporting/RuntimeTypeError.js.flow |   10 +
 src/index.js.flow                           |  209 +++
 src/oneOf.js.flow                           | 1447 +++++++++++++++++++
 src/typeConstraints.js.flow                 |   10 +
 src/types/AnyType.js.flow                   |    7 +
 src/types/ArrayType.js.flow                 |   11 +
 src/types/BooleanLiteralType.js.flow        |   11 +
 src/types/BooleanType.js.flow               |    7 +
 src/types/InstanceOfType.js.flow            |   11 +
 src/types/IntersectionType.js.flow          |   11 +
 src/types/NullLiteralType.js.flow           |    7 +
 src/types/NumberType.js.flow                |    7 +
 src/types/NumericLiteralType.js.flow        |   10 +
 src/types/ObjectType.js.flow                |   17 +
 src/types/ObjectTypeProperty.js.flow        |   27 +
 src/types/ObjectTypeProperty.ts             |    2 -
 src/types/RecordType.js.flow                |   14 +
 src/types/StringLiteralType.js.flow         |   11 +
 src/types/StringType.js.flow                |    7 +
 src/types/SymbolLiteralType.js.flow         |   11 +
 src/types/SymbolLiteralType.ts              |    2 -
 src/types/SymbolType.js.flow                |    7 +
 src/types/TupleType.js.flow                 |   11 +
 src/types/Type.js.flow                      |   29 +
 src/types/TypeAlias.js.flow                 |   18 +
 src/types/TypeReference.js.flow             |   12 +
 src/types/UndefinedLiteralType.js.flow      |    7 +
 src/types/UnionType.js.flow                 |   11 +
 tsconfig.json                               |    2 +-
 yarn.lock                                   |    5 +
 33 files changed, 1987 insertions(+), 5 deletions(-)
 create mode 100644 .flowconfig
 create mode 100644 src/Validation.js.flow
 create mode 100644 src/errorReporting/RuntimeTypeError.js.flow
 create mode 100644 src/index.js.flow
 create mode 100644 src/oneOf.js.flow
 create mode 100644 src/typeConstraints.js.flow
 create mode 100644 src/types/AnyType.js.flow
 create mode 100644 src/types/ArrayType.js.flow
 create mode 100644 src/types/BooleanLiteralType.js.flow
 create mode 100644 src/types/BooleanType.js.flow
 create mode 100644 src/types/InstanceOfType.js.flow
 create mode 100644 src/types/IntersectionType.js.flow
 create mode 100644 src/types/NullLiteralType.js.flow
 create mode 100644 src/types/NumberType.js.flow
 create mode 100644 src/types/NumericLiteralType.js.flow
 create mode 100644 src/types/ObjectType.js.flow
 create mode 100644 src/types/ObjectTypeProperty.js.flow
 create mode 100644 src/types/RecordType.js.flow
 create mode 100644 src/types/StringLiteralType.js.flow
 create mode 100644 src/types/StringType.js.flow
 create mode 100644 src/types/SymbolLiteralType.js.flow
 create mode 100644 src/types/SymbolType.js.flow
 create mode 100644 src/types/TupleType.js.flow
 create mode 100644 src/types/Type.js.flow
 create mode 100644 src/types/TypeAlias.js.flow
 create mode 100644 src/types/TypeReference.js.flow
 create mode 100644 src/types/UndefinedLiteralType.js.flow
 create mode 100644 src/types/UnionType.js.flow

diff --git a/.flowconfig b/.flowconfig
new file mode 100644
index 0000000..1fed445
--- /dev/null
+++ b/.flowconfig
@@ -0,0 +1,11 @@
+[ignore]
+
+[include]
+
+[libs]
+
+[lints]
+
+[options]
+
+[strict]
diff --git a/package.json b/package.json
index 47c42d1..766cdc2 100644
--- a/package.json
+++ b/package.json
@@ -127,6 +127,7 @@
     "eslint": "^5.9.0",
     "eslint-config-prettier": "^3.3.0",
     "eslint-watch": "^4.0.2",
+    "flow-bin": "^0.138.0",
     "husky": "^1.1.4",
     "istanbul": "^0.4.5",
     "lint-staged": "^8.0.4",
diff --git a/src/Validation.js.flow b/src/Validation.js.flow
new file mode 100644
index 0000000..fc3d8ee
--- /dev/null
+++ b/src/Validation.js.flow
@@ -0,0 +1,29 @@
+// @flow
+
+import Type from './types/Type'
+
+export type IdentifierPath = Array<string | number | symbol>
+
+export type ErrorTuple = [IdentifierPath, string, Type<any>]
+
+declare class Validation<T> {
+  input: T;
+
+  path: IdentifierPath;
+
+  prefix: string;
+
+  errors: ErrorTuple[];
+
+  constructor(input: T, prefix?: string, path?: IdentifierPath): void;
+
+  inCycle(type: Type<any>, input: any): boolean;
+
+  startCycle(type: Type<any>, input: any): void;
+
+  endCycle(type: Type<any>, input: any): void;
+
+  hasErrors(): boolean;
+}
+
+export default Validation
diff --git a/src/errorReporting/RuntimeTypeError.js.flow b/src/errorReporting/RuntimeTypeError.js.flow
new file mode 100644
index 0000000..59b9cf8
--- /dev/null
+++ b/src/errorReporting/RuntimeTypeError.js.flow
@@ -0,0 +1,10 @@
+// @flow
+
+import { type ErrorTuple } from '../Validation'
+
+declare class RuntimeTypeError extends TypeError {
+  errors: ?(ErrorTuple[]);
+  constructor(message: string, options?: { errors?: ?(ErrorTuple[]) }): void;
+}
+
+export default RuntimeTypeError
diff --git a/src/index.js.flow b/src/index.js.flow
new file mode 100644
index 0000000..ae88050
--- /dev/null
+++ b/src/index.js.flow
@@ -0,0 +1,209 @@
+// @flow
+
+import Type from './types/Type'
+import AnyType from './types/AnyType'
+import ArrayType from './types/ArrayType'
+import BooleanLiteralType from './types/BooleanLiteralType'
+import BooleanType from './types/BooleanType'
+import InstanceOfType from './types/InstanceOfType'
+import IntersectionType from './types/IntersectionType'
+import NullLiteralType from './types/NullLiteralType'
+import UndefinedLiteralType from './types/UndefinedLiteralType'
+import NumberType from './types/NumberType'
+import NumericLiteralType from './types/NumericLiteralType'
+import ObjectType from './types/ObjectType'
+import ObjectTypeProperty from './types/ObjectTypeProperty'
+import RecordType from './types/RecordType'
+import StringLiteralType from './types/StringLiteralType'
+import StringType from './types/StringType'
+import SymbolLiteralType from './types/SymbolLiteralType'
+import SymbolType from './types/SymbolType'
+import TupleType from './types/TupleType'
+import UnionType from './types/UnionType'
+import TypeAlias from './types/TypeAlias'
+import TypeReference from './types/TypeReference'
+import Validation from './Validation'
+import RuntimeTypeError from './errorReporting/RuntimeTypeError'
+import oneOf from './oneOf'
+
+export {
+  Type,
+  AnyType,
+  ArrayType,
+  BooleanLiteralType,
+  BooleanType,
+  InstanceOfType,
+  IntersectionType,
+  NullLiteralType,
+  UndefinedLiteralType,
+  NumberType,
+  NumericLiteralType,
+  ObjectType,
+  ObjectTypeProperty,
+  RecordType,
+  StringLiteralType,
+  StringType,
+  SymbolLiteralType,
+  SymbolType,
+  TupleType,
+  UnionType,
+  TypeAlias,
+  TypeReference,
+  Validation,
+  RuntimeTypeError,
+  oneOf,
+}
+
+declare export function any(): Type<any>
+
+declare export function array<T>(elementType: Type<T>): Type<T[]>
+
+declare export function nullLiteral(): Type<null>
+export { nullLiteral as null }
+declare export function nullOr<T>(type: Type<T>): Type<T | null>
+
+declare export function undefinedLiteral(): Type<void>
+export { undefinedLiteral as undefined }
+
+declare export function nullish<T>(type: Type<T>): Type<?T>
+declare export function nullishOr<T>(type: Type<T>): Type<?T>
+
+declare export function boolean(): Type<boolean>
+declare export function boolean<T: true | false>(literal: T): Type<T>
+declare export function boolean(
+  literal?: boolean
+): Type<boolean> | Type<true> | Type<false>
+
+declare export function number(): Type<number>
+declare export function number<T: number>(literal: T): Type<T>
+declare export function number(
+  literal?: number
+): Type<number> | Type<true> | Type<false>
+
+declare export function string(): Type<string>
+declare export function string<T: string>(literal: T): Type<T>
+declare export function string(
+  literal?: string
+): Type<string> | Type<true> | Type<false>
+
+declare export function symbol(): Type<symbol>
+declare export function symbol<T: symbol>(literal: T): Type<T>
+declare export function symbol(
+  literal?: symbol
+): Type<symbol> | Type<true> | Type<false>
+
+type OptionalProperty<T> = { __optional__: Type<T> }
+
+declare export function optional<T>(type: Type<T>): OptionalProperty<T>
+
+declare export function optionalNullOr<T>(
+  type: Type<T>
+): OptionalProperty<T | null>
+
+type OptionalKeys<T> = {
+  [K in keyof T]: T extends Record<K, T[K]> ? never : K
+} extends {
+  [_ in keyof T]: infer U
+}
+  ? {} extends U
+    ? never
+    : U
+  : never
+
+export const object = <S extends Record<string | number | symbol, unknown>>({
+  exact,
+}: { exact?: boolean } = {}) => <
+  P extends {
+    [K in keyof S]-?: K extends OptionalKeys<S>
+      ? OptionalProperty<any>
+      : Type<any>
+  }
+>(
+  properties: P
+): ObjectType<
+  {
+    [K in keyof S]: P[K] extends OptionalProperty<infer T>
+      ? T
+      : P[K] extends Type<infer T>
+      ? T
+      : never
+  }
+> =>
+  new ObjectType(
+    [...Object.entries(properties)].map(
+      ([key, type]) =>
+        new ObjectTypeProperty(
+          key,
+          getOptional(type) || (type as Type<any>),
+          Boolean(getOptional(type))
+        )
+    ),
+    exact
+  ) as any
+
+type Properties = { [string | number | symbol]: Type<any> }
+
+declare export function simpleObject<Required: Properties>(
+  required: Required,
+  options: ?{ exact?: boolean }
+): ObjectType<$ObjMap<Required, <T>(T) => $PropertyType<T, '__type'>>>
+
+declare export function record<K: string | number | symbol, V>(
+  key: Type<K>,
+  value: Type<V>
+): RecordType<K, V>
+
+declare export function instanceOf<T>(classType: {
+  new(...args: any[]): T,
+}): Type<T>
+
+declare export function tuple<T: Type<any>[]>(
+  ...types: T
+): Type<$TupleMap<T, <T>(T) => $PropertyType<T, '__type'>>>
+
+declare export function allOf<T1>(...types: [Type<T1>]): Type<T1>
+declare export function allOf<T1, T2>(
+  ...types: [Type<T1>, Type<T2>]
+): Type<T1 & T2>
+declare export function allOf<T1, T2, T3>(
+  ...types: [Type<T1>, Type<T2>, Type<T3>]
+): Type<T1 & T2 & T3>
+declare export function allOf<T1, T2, T3, T4>(
+  ...types: [Type<T1>, Type<T2>, Type<T3>, Type<T4>]
+): Type<T1 & T2 & T3 & T4>
+declare export function allOf<T1, T2, T3, T4, T5>(
+  ...types: [Type<T1>, Type<T2>, Type<T3>, Type<T4>, Type<T5>]
+): Type<T1 & T2 & T3 & T4 & T5>
+declare export function allOf<T1, T2, T3, T4, T5, T6>(
+  ...types: [Type<T1>, Type<T2>, Type<T3>, Type<T4>, Type<T5>, Type<T6>]
+): Type<T1 & T2 & T3 & T4 & T5 & T6>
+declare export function allOf<T1, T2, T3, T4, T5, T6, T7>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>
+  ]
+): Type<T1 & T2 & T3 & T4 & T5 & T6 & T7>
+declare export function allOf<T1, T2, T3, T4, T5, T6, T7, T8>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>
+  ]
+): Type<T1 & T2 & T3 & T4 & T5 & T6 & T7 & T8>
+declare export function allOf(...types: Type<any>[]): Type<any>
+
+declare export function alias<T>(name: string, type: Type<T>): TypeAlias<T>
+
+declare export function ref<T>(type: () => TypeAlias<T>): Type<T>
+
+export type ExtractType<T: Type<any>> = $PropertyType<T, '__type'>
diff --git a/src/oneOf.js.flow b/src/oneOf.js.flow
new file mode 100644
index 0000000..19495d1
--- /dev/null
+++ b/src/oneOf.js.flow
@@ -0,0 +1,1447 @@
+// @flow
+
+import Type from './types/Type'
+import UnionType from './types/UnionType'
+
+declare function oneOf<T1>(...types: [Type<T1>]): Type<T1>
+
+declare function oneOf<T1, T2>(...types: [Type<T1>, Type<T2>]): Type<T1 | T2>
+
+declare function oneOf<T1, T2, T3>(
+  ...types: [Type<T1>, Type<T2>, Type<T3>]
+): Type<T1 | T2 | T3>
+
+declare function oneOf<T1, T2, T3, T4>(
+  ...types: [Type<T1>, Type<T2>, Type<T3>, Type<T4>]
+): Type<T1 | T2 | T3 | T4>
+
+declare function oneOf<T1, T2, T3, T4, T5>(
+  ...types: [Type<T1>, Type<T2>, Type<T3>, Type<T4>, Type<T5>]
+): Type<T1 | T2 | T3 | T4 | T5>
+
+declare function oneOf<T1, T2, T3, T4, T5, T6>(
+  ...types: [Type<T1>, Type<T2>, Type<T3>, Type<T4>, Type<T5>, Type<T6>]
+): Type<T1 | T2 | T3 | T4 | T5 | T6>
+
+declare function oneOf<T1, T2, T3, T4, T5, T6, T7>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>
+  ]
+): Type<T1 | T2 | T3 | T4 | T5 | T6 | T7>
+
+declare function oneOf<T1, T2, T3, T4, T5, T6, T7, T8>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>
+  ]
+): Type<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8>
+
+declare function oneOf<T1, T2, T3, T4, T5, T6, T7, T8, T9>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>
+  ]
+): Type<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9>
+
+declare function oneOf<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>
+  ]
+): Type<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9 | T10>
+
+declare function oneOf<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>
+  ]
+): Type<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9 | T10 | T11>
+
+declare function oneOf<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>
+  ]
+): Type<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9 | T10 | T11 | T12>
+
+declare function oneOf<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>
+  ]
+): Type<T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9 | T10 | T11 | T12 | T13>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>
+  ]
+): Type<
+  T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9 | T10 | T11 | T12 | T13 | T14
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>
+  ]
+): Type<
+  T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9 | T10 | T11 | T12 | T13 | T14 | T15
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21,
+  T22
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>,
+    Type<T22>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+  | T22
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21,
+  T22,
+  T23
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>,
+    Type<T22>,
+    Type<T23>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+  | T22
+  | T23
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21,
+  T22,
+  T23,
+  T24
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>,
+    Type<T22>,
+    Type<T23>,
+    Type<T24>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+  | T22
+  | T23
+  | T24
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21,
+  T22,
+  T23,
+  T24,
+  T25
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>,
+    Type<T22>,
+    Type<T23>,
+    Type<T24>,
+    Type<T25>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+  | T22
+  | T23
+  | T24
+  | T25
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21,
+  T22,
+  T23,
+  T24,
+  T25,
+  T26
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>,
+    Type<T22>,
+    Type<T23>,
+    Type<T24>,
+    Type<T25>,
+    Type<T26>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+  | T22
+  | T23
+  | T24
+  | T25
+  | T26
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21,
+  T22,
+  T23,
+  T24,
+  T25,
+  T26,
+  T27
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>,
+    Type<T22>,
+    Type<T23>,
+    Type<T24>,
+    Type<T25>,
+    Type<T26>,
+    Type<T27>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+  | T22
+  | T23
+  | T24
+  | T25
+  | T26
+  | T27
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21,
+  T22,
+  T23,
+  T24,
+  T25,
+  T26,
+  T27,
+  T28
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>,
+    Type<T22>,
+    Type<T23>,
+    Type<T24>,
+    Type<T25>,
+    Type<T26>,
+    Type<T27>,
+    Type<T28>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+  | T22
+  | T23
+  | T24
+  | T25
+  | T26
+  | T27
+  | T28
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21,
+  T22,
+  T23,
+  T24,
+  T25,
+  T26,
+  T27,
+  T28,
+  T29
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>,
+    Type<T22>,
+    Type<T23>,
+    Type<T24>,
+    Type<T25>,
+    Type<T26>,
+    Type<T27>,
+    Type<T28>,
+    Type<T29>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+  | T22
+  | T23
+  | T24
+  | T25
+  | T26
+  | T27
+  | T28
+  | T29
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21,
+  T22,
+  T23,
+  T24,
+  T25,
+  T26,
+  T27,
+  T28,
+  T29,
+  T30
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>,
+    Type<T22>,
+    Type<T23>,
+    Type<T24>,
+    Type<T25>,
+    Type<T26>,
+    Type<T27>,
+    Type<T28>,
+    Type<T29>,
+    Type<T30>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+  | T22
+  | T23
+  | T24
+  | T25
+  | T26
+  | T27
+  | T28
+  | T29
+  | T30
+>
+
+declare function oneOf<
+  T1,
+  T2,
+  T3,
+  T4,
+  T5,
+  T6,
+  T7,
+  T8,
+  T9,
+  T10,
+  T11,
+  T12,
+  T13,
+  T14,
+  T15,
+  T16,
+  T17,
+  T18,
+  T19,
+  T20,
+  T21,
+  T22,
+  T23,
+  T24,
+  T25,
+  T26,
+  T27,
+  T28,
+  T29,
+  T30,
+  T31
+>(
+  ...types: [
+    Type<T1>,
+    Type<T2>,
+    Type<T3>,
+    Type<T4>,
+    Type<T5>,
+    Type<T6>,
+    Type<T7>,
+    Type<T8>,
+    Type<T9>,
+    Type<T10>,
+    Type<T11>,
+    Type<T12>,
+    Type<T13>,
+    Type<T14>,
+    Type<T15>,
+    Type<T16>,
+    Type<T17>,
+    Type<T18>,
+    Type<T19>,
+    Type<T20>,
+    Type<T21>,
+    Type<T22>,
+    Type<T23>,
+    Type<T24>,
+    Type<T25>,
+    Type<T26>,
+    Type<T27>,
+    Type<T28>,
+    Type<T29>,
+    Type<T30>,
+    Type<T31>
+  ]
+): Type<
+  | T1
+  | T2
+  | T3
+  | T4
+  | T5
+  | T6
+  | T7
+  | T8
+  | T9
+  | T10
+  | T11
+  | T12
+  | T13
+  | T14
+  | T15
+  | T16
+  | T17
+  | T18
+  | T19
+  | T20
+  | T21
+  | T22
+  | T23
+  | T24
+  | T25
+  | T26
+  | T27
+  | T28
+  | T29
+  | T30
+  | T31
+>
+
+declare function oneOf(...types: Type<any>[]): Type<any>
+
+export default oneOf
diff --git a/src/typeConstraints.js.flow b/src/typeConstraints.js.flow
new file mode 100644
index 0000000..fda0283
--- /dev/null
+++ b/src/typeConstraints.js.flow
@@ -0,0 +1,10 @@
+// @flow
+
+import Type from './types/Type'
+import Validation, { type ErrorTuple, type IdentifierPath } from './Validation'
+
+export type TypeConstraint<T> = (input: T) => ?string
+
+export interface ConstrainableType<T> extends Type<T> {
+  constraints: TypeConstraint<T>[];
+}
diff --git a/src/types/AnyType.js.flow b/src/types/AnyType.js.flow
new file mode 100644
index 0000000..d0d6e18
--- /dev/null
+++ b/src/types/AnyType.js.flow
@@ -0,0 +1,7 @@
+// @flow
+
+import Type from './Type'
+
+declare class AnyType extends Type<any> {}
+
+export default AnyType
diff --git a/src/types/ArrayType.js.flow b/src/types/ArrayType.js.flow
new file mode 100644
index 0000000..acfeabf
--- /dev/null
+++ b/src/types/ArrayType.js.flow
@@ -0,0 +1,11 @@
+// @flow
+
+import Type from './Type'
+
+declare class ArrayType<T> extends Type<Array<T>> {
+  elementType: Type<T>;
+
+  constructor(elementType: Type<T>): void;
+}
+
+export default ArrayType
diff --git a/src/types/BooleanLiteralType.js.flow b/src/types/BooleanLiteralType.js.flow
new file mode 100644
index 0000000..18bd218
--- /dev/null
+++ b/src/types/BooleanLiteralType.js.flow
@@ -0,0 +1,11 @@
+// @flow
+
+import Type from './Type'
+
+declare class BooleanLiteralType<T: boolean> extends Type<T> {
+  value: T;
+
+  constructor(value: T): void;
+}
+
+export default BooleanLiteralType
diff --git a/src/types/BooleanType.js.flow b/src/types/BooleanType.js.flow
new file mode 100644
index 0000000..990b845
--- /dev/null
+++ b/src/types/BooleanType.js.flow
@@ -0,0 +1,7 @@
+// @flow
+
+import Type from './Type'
+
+declare class BooleanType extends Type<boolean> {}
+
+export default BooleanType
diff --git a/src/types/InstanceOfType.js.flow b/src/types/InstanceOfType.js.flow
new file mode 100644
index 0000000..43e0a6a
--- /dev/null
+++ b/src/types/InstanceOfType.js.flow
@@ -0,0 +1,11 @@
+// @flow
+
+import Type from './Type'
+
+declare class InstanceOfType<T: Class<any>> extends Type<T> {
+  classType: T;
+
+  constructor(classType: T): void;
+}
+
+export default InstanceOfType
diff --git a/src/types/IntersectionType.js.flow b/src/types/IntersectionType.js.flow
new file mode 100644
index 0000000..afcd22d
--- /dev/null
+++ b/src/types/IntersectionType.js.flow
@@ -0,0 +1,11 @@
+// @flow
+
+import Type from './Type'
+
+declare class IntersectionType<T> extends Type<T> {
+  types: Type<any>[];
+
+  constructor(types: Type<any>[]): void;
+}
+
+export default IntersectionType
diff --git a/src/types/NullLiteralType.js.flow b/src/types/NullLiteralType.js.flow
new file mode 100644
index 0000000..210330f
--- /dev/null
+++ b/src/types/NullLiteralType.js.flow
@@ -0,0 +1,7 @@
+// @flow
+
+import Type from './Type'
+
+declare class NullLiteralType extends Type<null> {}
+
+export default NullLiteralType
diff --git a/src/types/NumberType.js.flow b/src/types/NumberType.js.flow
new file mode 100644
index 0000000..0ee47a6
--- /dev/null
+++ b/src/types/NumberType.js.flow
@@ -0,0 +1,7 @@
+// @flow
+
+import Type from './Type'
+
+declare class NumberType extends Type<number> {}
+
+export default NumberType
diff --git a/src/types/NumericLiteralType.js.flow b/src/types/NumericLiteralType.js.flow
new file mode 100644
index 0000000..91fae58
--- /dev/null
+++ b/src/types/NumericLiteralType.js.flow
@@ -0,0 +1,10 @@
+// @flow
+
+import Type from './Type'
+
+declare class NumericLiteralType<T: number> extends Type<T> {
+  value: T;
+
+  constructor(value: T): void;
+}
+export default NumericLiteralType
diff --git a/src/types/ObjectType.js.flow b/src/types/ObjectType.js.flow
new file mode 100644
index 0000000..78cc8fb
--- /dev/null
+++ b/src/types/ObjectType.js.flow
@@ -0,0 +1,17 @@
+// @flow
+
+import Type from './Type'
+
+import ObjectTypeProperty from './ObjectTypeProperty'
+
+declare class ObjectType<T: {}> extends Type<T> {
+  properties: ObjectTypeProperty<$Keys<T>, any>[];
+  exact: boolean;
+
+  constructor(
+    properties?: ObjectTypeProperty<$Keys<T>, any>[],
+    exact?: boolean
+  ): void;
+}
+
+export default ObjectType
diff --git a/src/types/ObjectTypeProperty.js.flow b/src/types/ObjectTypeProperty.js.flow
new file mode 100644
index 0000000..3169f08
--- /dev/null
+++ b/src/types/ObjectTypeProperty.js.flow
@@ -0,0 +1,27 @@
+// @flow
+
+import Type from './Type'
+
+import { type TypeConstraint } from '../typeConstraints'
+
+declare class ObjectTypeProperty<
+  K: string | number | symbol,
+  V
+> extends Type<V> {
+  key: K;
+  value: Type<V>;
+  optional: boolean;
+  constraints: TypeConstraint<V>[];
+  __objectType: Type<any>;
+
+  constructor(key: K, value: Type<V>, optional: boolean): void;
+
+  addConstraint(...constraints: TypeConstraint<V>[]): ObjectTypeProperty<K, V>;
+
+  /**
+   * Determine whether the property exists on the given input or its prototype chain.
+   */
+  existsOn(input: { [string]: any }): boolean;
+}
+
+export default ObjectTypeProperty
diff --git a/src/types/ObjectTypeProperty.ts b/src/types/ObjectTypeProperty.ts
index 155d865..79beb22 100644
--- a/src/types/ObjectTypeProperty.ts
+++ b/src/types/ObjectTypeProperty.ts
@@ -1,5 +1,3 @@
-/* @flow */
-
 import Type from './Type'
 import {
   addConstraints,
diff --git a/src/types/RecordType.js.flow b/src/types/RecordType.js.flow
new file mode 100644
index 0000000..e821a03
--- /dev/null
+++ b/src/types/RecordType.js.flow
@@ -0,0 +1,14 @@
+// @flow
+
+import Type from './Type'
+
+declare class RecordType<K: string | number | symbol, V> extends Type<{
+  [K]: V,
+}> {
+  key: Type<K>;
+  value: Type<V>;
+
+  constructor(key: Type<K>, value: Type<V>): void;
+}
+
+export default RecordType
diff --git a/src/types/StringLiteralType.js.flow b/src/types/StringLiteralType.js.flow
new file mode 100644
index 0000000..3b400df
--- /dev/null
+++ b/src/types/StringLiteralType.js.flow
@@ -0,0 +1,11 @@
+// @flow
+
+import Type from './Type'
+
+declare class StringLiteralType<T: string> extends Type<T> {
+  value: T;
+
+  constructor(value: T): void;
+}
+
+export default StringLiteralType
diff --git a/src/types/StringType.js.flow b/src/types/StringType.js.flow
new file mode 100644
index 0000000..4847bc8
--- /dev/null
+++ b/src/types/StringType.js.flow
@@ -0,0 +1,7 @@
+// @flow
+
+import Type from './Type'
+
+declare class StringType extends Type<string> {}
+
+export default StringType
diff --git a/src/types/SymbolLiteralType.js.flow b/src/types/SymbolLiteralType.js.flow
new file mode 100644
index 0000000..e5eea53
--- /dev/null
+++ b/src/types/SymbolLiteralType.js.flow
@@ -0,0 +1,11 @@
+// @flow
+
+import Type from './Type'
+
+declare class SymbolLiteralType<T: symbol> extends Type<T> {
+  value: T;
+
+  constructor(value: T): void;
+}
+
+export default SymbolLiteralType
diff --git a/src/types/SymbolLiteralType.ts b/src/types/SymbolLiteralType.ts
index d38d48c..b597d78 100644
--- a/src/types/SymbolLiteralType.ts
+++ b/src/types/SymbolLiteralType.ts
@@ -1,5 +1,3 @@
-/* @flow */
-
 import Type from './Type'
 import getErrorMessage from '../getErrorMessage'
 import Validation, { ErrorTuple, IdentifierPath } from '../Validation'
diff --git a/src/types/SymbolType.js.flow b/src/types/SymbolType.js.flow
new file mode 100644
index 0000000..c1f137d
--- /dev/null
+++ b/src/types/SymbolType.js.flow
@@ -0,0 +1,7 @@
+// @flow
+
+import Type from './Type'
+
+declare class SymbolType extends Type<symbol> {}
+
+export default SymbolType
diff --git a/src/types/TupleType.js.flow b/src/types/TupleType.js.flow
new file mode 100644
index 0000000..6a11bca
--- /dev/null
+++ b/src/types/TupleType.js.flow
@@ -0,0 +1,11 @@
+// @flow
+
+import Type from './Type'
+
+declare class TupleType<T: any[]> extends Type<T> {
+  types: $TupleMap<T, <E>(E) => Type<E>>;
+
+  constructor(types: $TupleMap<T, <E>(E) => Type<E>>): void;
+}
+
+export default TupleType
diff --git a/src/types/Type.js.flow b/src/types/Type.js.flow
new file mode 100644
index 0000000..b42aeb2
--- /dev/null
+++ b/src/types/Type.js.flow
@@ -0,0 +1,29 @@
+// @flow
+
+import type Validation from '../Validation'
+import type { ErrorTuple, IdentifierPath } from '../Validation'
+
+/**
+ * # Type
+ *
+ * This is the base class for all types.
+ */
+declare class Type<T> {
+  typeName: string;
+
+  errors(
+    validation: Validation<any>,
+    path: IdentifierPath,
+    input: any
+  ): Generator<ErrorTuple, void, void>;
+
+  accepts(input: any): boolean;
+
+  assert<V: T>(input: any, prefix?: string, path?: IdentifierPath): V;
+
+  validate(input: any, prefix?: string, path?: IdentifierPath): Validation<T>;
+
+  toString(): string;
+}
+
+export default Type
diff --git a/src/types/TypeAlias.js.flow b/src/types/TypeAlias.js.flow
new file mode 100644
index 0000000..670879f
--- /dev/null
+++ b/src/types/TypeAlias.js.flow
@@ -0,0 +1,18 @@
+// @flow
+
+import Type from './Type'
+import { type TypeConstraint } from '../typeConstraints'
+
+declare class TypeAlias<T> extends Type<T> {
+  name: string;
+  type: Type<T>;
+  constraints: TypeConstraint<T>[];
+
+  constructor(name: string, type: Type<T>): void;
+
+  addConstraint(...constraints: TypeConstraint<T>[]): this;
+
+  get hasConstraints(): boolean;
+}
+
+export default TypeAlias
diff --git a/src/types/TypeReference.js.flow b/src/types/TypeReference.js.flow
new file mode 100644
index 0000000..0b5551a
--- /dev/null
+++ b/src/types/TypeReference.js.flow
@@ -0,0 +1,12 @@
+// @flow
+
+import Type from './Type'
+import TypeAlias from './TypeAlias'
+
+declare class TypeReference<T> extends Type<T> {
+  type: () => TypeAlias<T>;
+
+  constructor(type: () => TypeAlias<T>): void;
+}
+
+export default TypeReference
diff --git a/src/types/UndefinedLiteralType.js.flow b/src/types/UndefinedLiteralType.js.flow
new file mode 100644
index 0000000..464f228
--- /dev/null
+++ b/src/types/UndefinedLiteralType.js.flow
@@ -0,0 +1,7 @@
+// @flow
+
+import Type from './Type'
+
+declare class UndefinedLiteralType extends Type<void> {}
+
+export default UndefinedLiteralType
diff --git a/src/types/UnionType.js.flow b/src/types/UnionType.js.flow
new file mode 100644
index 0000000..9e63d4f
--- /dev/null
+++ b/src/types/UnionType.js.flow
@@ -0,0 +1,11 @@
+// @flow
+
+import Type from './Type'
+
+declare class UnionType<T> extends Type<T> {
+  types: Type<any>[];
+
+  constructor(types: Type<any>[]): void;
+}
+
+export default UnionType
diff --git a/tsconfig.json b/tsconfig.json
index 3667e9a..217fbeb 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,5 +1,5 @@
 {
-  "include": ["./src"],
+  "include": ["./src/**/*.ts"],
   "exclude": ["node_modules", "./src/**/*.spec.ts", "./test"],
   "compilerOptions": {
     /* Basic Options */
diff --git a/yarn.lock b/yarn.lock
index 94ce0df..9a3a73e 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3531,6 +3531,11 @@ flatted@^2.0.0:
   resolved "https://registry.yarnpkg.com/flatted/-/flatted-2.0.1.tgz#69e57caa8f0eacbc281d2e2cb458d46fdb449e08"
   integrity sha512-a1hQMktqW9Nmqr5aktAux3JMNqaucxGcjtjWnZLHX7yyPCmlSV3M54nGYbqT8K+0GhF3NBgmJCc3ma+WOgX8Jg==
 
+flow-bin@^0.138.0:
+  version "0.138.0"
+  resolved "https://registry.npmjs.org/flow-bin/-/flow-bin-0.138.0.tgz#a0c81a3dd1ed34771b33b7e91078ed260301aa17"
+  integrity sha512-y3twwNeN0FWEK0vvJo/5SiC/OQVlhubGRyOPIS6p49b2yiiWE/cBFG/aC9kFXFfh7Orewe5O5B2X0+IiEOCYIw==
+
 flush-write-stream@^1.0.0:
   version "1.1.1"
   resolved "https://registry.yarnpkg.com/flush-write-stream/-/flush-write-stream-1.1.1.tgz#8dd7d873a1babc207d94ead0c2e0e44276ebf2e8"