diff --git a/packages/argparse/src/argparse.test.ts b/packages/argparse/src/argparse.test.ts
index f374630..fa18bad 100644
--- a/packages/argparse/src/argparse.test.ts
+++ b/packages/argparse/src/argparse.test.ts
@@ -1,17 +1,11 @@
-import {argparse, IArgsConfig} from './argparse'
+import {argparse, arg, IArgsConfig} from './argparse'
 
 describe('argparse', () => {
 
   it('parses args', () => {
     const args = argparse({
-      one: {
-        type: 'string',
-        required: true,
-      },
-      two: {
-        type: 'number',
-        default: 1,
-      },
+      one: arg('string', {required: true}),
+      two: arg('number', {default: 100}),
       four: {
         type: 'boolean',
       },
@@ -125,6 +119,29 @@ describe('argparse', () => {
     })
   })
 
+  describe('choices', () => {
+    it('can enforce typed choices', () => {
+      const parse = argparse({
+        choice: arg('string', {
+          choices: ['a', 'b'],
+        }),
+        num: arg('number', {
+          choices: [1, 2],
+        }),
+      })
+      expect(() => parse(['--choice', 'c'])).toThrowError(/one of: a, b$/)
+      expect(() => parse(['--num', '3'])).toThrowError(/must be one of: 1, 2$/)
+      expect(parse(['--choice', 'a', '--num', '1'])).toEqual({
+        choice: 'a',
+        num: 1,
+      })
+      expect(parse(['--choice', 'b', '--num', '2'])).toEqual({
+        choice: 'b',
+        num: 2,
+      })
+    })
+  })
+
   describe('positional', () => {
     it('can be defined', () => {
       const parse = argparse({
diff --git a/packages/argparse/src/argparse.ts b/packages/argparse/src/argparse.ts
index 1eed3a2..6e4eaba 100644
--- a/packages/argparse/src/argparse.ts
+++ b/packages/argparse/src/argparse.ts
@@ -8,15 +8,19 @@ export type TArgType<T extends TArgTypeName> =
   ? boolean
   : never
 
-export interface IArgConfig<T extends TArgTypeName> {
-  type: T
+export interface IArgParam<T extends TArgTypeName> {
   alias?: string
   description?: string
   default?: TArgType<T>
+  choices?: Array<TArgType<T>>
   required?: boolean
   positional?: boolean
 }
 
+export interface IArgConfig<T extends TArgTypeName> extends IArgParam<T> {
+  type: T
+}
+
 export interface IArgsConfig {
   [arg: string]: IArgConfig<TArgTypeName>
 }
@@ -26,7 +30,13 @@ export type TArgs<T extends IArgsConfig> = {
     TArgType<A> : never
 }
 
-const iterate = <T>(arr: T[]) => {
+interface IIterator<T> {
+  hasNext(): boolean
+  next(): T
+  peek(): T
+}
+
+const iterate = <T>(arr: T[]): IIterator<T> => {
   let i = -1
   return {
     hasNext() {
@@ -58,6 +68,88 @@ function getDefaultValue(type: TArgTypeName) {
   }
 }
 
+function getBooleanValue(
+  it: IIterator<string>,
+  argument: string,
+  isPositional: boolean,
+): boolean {
+  if (isPositional) {
+    if (argument === 'true') {
+      return true
+    } else if (argument === 'false') {
+      return false
+    } else {
+      throw new Error('Value of argument must be true or false: ' + arg)
+    }
+  }
+  const peek = it.peek()
+  if (peek === 'true') {
+    it.next()
+    return true
+  } else if (peek === 'false') {
+    it.next()
+    return false
+  } else {
+    return true
+  }
+}
+
+function getValue(
+  it: IIterator<string>,
+  argument: string,
+  isPositional: boolean,
+): string {
+  return isPositional ? argument : it.next()
+}
+
+function checkChoice<T>(argument: string, choice: T, choices?: T[]) {
+  if (choices) {
+    assert(
+      choices.some(c => choice === c),
+      `Argument "${argument}" must be one of: ${choices.join(', ')}`)
+  }
+}
+
+export function padRight(str: string, chars: number) {
+  while (str.length < chars) {
+    str += ' '
+  }
+  return str
+}
+
+export function help(config: IArgsConfig) {
+  return Object.keys(config).map(argument => {
+    const argConfig = config[argument]
+    const {alias, description, type} = argConfig
+    const name = alias
+      ? `-${alias}, --${argument}`
+      : `    --${argument}`
+    const samples = []
+    if (argConfig.required) {
+      samples.push('required')
+    }
+    if (argConfig.default) {
+      samples.push('default: ' + argConfig.default)
+    }
+    if (argConfig.choices) {
+      samples.push('choices: ' + argConfig.choices)
+    }
+    const sample = samples.length ? ` (${samples.join(', ')})` : ''
+    return padRight(name + ' ' + type, 20) + ' ' + description + sample
+  })
+  .join('\n')
+}
+
+export function arg<T extends TArgTypeName>(
+  type: T,
+  config: IArgParam<T> = {},
+): IArgConfig<T> {
+  return {
+    ...config,
+    type,
+  }
+}
+
 export const argparse = <T extends IArgsConfig>(
   config: T,
 ) => (args: string[]): TArgs<T> => {
@@ -66,22 +158,24 @@ export const argparse = <T extends IArgsConfig>(
 
   const aliases: Record<string, string> = {}
   const positional: string[] = []
-  const requiredArgs = Object.keys(config).reduce((obj, arg) => {
-    const argConfig = config[arg]
-    result[arg] = argConfig.default !== undefined
+  const requiredArgs = Object.keys(config).reduce((obj, argument) => {
+    const argConfig = config[argument]
+    result[argument] = argConfig.default !== undefined
       ? argConfig.default
       : getDefaultValue(argConfig.type)
     if (argConfig.alias) {
+      assert(argConfig.alias.length === 1,
+        'Alias must be a single character: ' + argConfig.alias)
       assert(
         argConfig.alias in aliases === false,
         'Duplicate alias: ' + argConfig.alias)
-      aliases[argConfig.alias] = arg
+      aliases[argConfig.alias] = argument
     }
     if (argConfig.positional) {
-      positional.push(arg)
+      positional.push(argument)
     }
     if (argConfig.required) {
-      obj[arg] = true
+      obj[argument] = true
     }
     return obj
   }, {} as Record<string, true>)
@@ -90,12 +184,12 @@ export const argparse = <T extends IArgsConfig>(
     return nameOrAlias in config ? nameOrAlias : aliases[nameOrAlias]
   }
 
-  function processFlags(arg: string): string {
-    if (arg.substring(1, 2) === '-') {
-      return arg.substring(2)
+  function processFlags(argument: string): string {
+    if (argument.substring(1, 2) === '-') {
+      return argument.substring(2)
     }
 
-    const flags = arg.substring(1).split('')
+    const flags = argument.substring(1).split('')
 
     flags.slice(0, flags.length - 1)
     .forEach(flag => {
@@ -120,53 +214,32 @@ export const argparse = <T extends IArgsConfig>(
   }
 
   while (it.hasNext()) {
-    const arg = it.next()
-    const isPositional = arg.substring(0, 1) !== '-'
+    const argument = it.next()
+    const isPositional = argument.substring(0, 1) !== '-'
     const argName = !isPositional
-      ? processFlags(arg)
+      ? processFlags(argument)
       : getNextPositional()
     const argConfig = config[argName]
-    assert(!!argConfig, 'Unknown argument: ' + arg)
+    assert(!!argConfig, 'Unknown argument: ' + argument)
     delete requiredArgs[argName]
-    const peek = it.peek()
     switch (argConfig.type) {
       case 'string':
-        if (isPositional) {
-          result[argName] = arg
-        } else {
-          assert(it.hasNext(), 'Value of argument must be a string: ' + arg)
-          result[argName] = it.next()
-        }
-        continue
+        result[argName] = getValue(it, argument, isPositional)
+        assert(!!result[argName],
+          'Value of argument must be a string: ' + argument)
+        break
       case 'number':
-        const num = parseInt(isPositional ? arg : it.next(), 10)
-        assert(!isNaN(num), 'Value of argument must be a number: ' + arg)
+        const num = parseInt(getValue(it, argument, isPositional), 10)
+        assert(!isNaN(num), 'Value of argument must be a number: ' + argument)
         result[argName] = num
-        continue
+        break
       case 'boolean':
-        if (isPositional) {
-          if (arg === 'true') {
-            result[argName] = true
-          } else if (arg === 'false') {
-            result[argName] = false
-          } else {
-            assert(false, 'Value of argument must be true or false: ' + arg)
-          }
-          continue
-        }
-        if (peek === 'true') {
-          it.next()
-          result[argName] = true
-        } else if (peek === 'false') {
-          it.next()
-          result[argName] = false
-        } else {
-          result[argName] = true
-        }
-        continue
+        result[argName] = getBooleanValue(it, argument, isPositional)
+        break
       default:
         assert(false, 'Unknown type: ' + argConfig.type)
     }
+    checkChoice(argument, result[argName], argConfig.choices)
   }
 
   assert(!Object.keys(requiredArgs).length, 'Missing required args: ' +