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September 12, 2012 12:23
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A bottom up approach to category theory: Functors
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case class Contact(name: String, email: String) |
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def byId(id: Long): Option[Contact] | |
def all: List[Contact] |
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def listMap[A, B](f: A => B)(xs: List[A]): List[B] = xs match { | |
case Nil => Nil | |
case x :: xs => f(x) :: listMap(f)(xs) | |
} |
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def listMap[A, B](f: A => B, xs: List[A]): List[B] = xs match { | |
case Nil => Nil | |
case x :: xs => f(x) :: listMap(f, xs) | |
} |
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def listToJson(contacts: List[Contact]): List[JsObject] = contacts match { | |
case Nil => Nil | |
case c :: cs => | |
val contactJson = Json.obj( | |
"name" -> c.name, | |
"email" -> c.email | |
) | |
contactJson :: listToJson(cs) | |
} |
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object Application extends Controller { | |
def list = Action { | |
Ok(<contacts>{ listToXml(Contacts.all) }</contacts>) | |
} | |
def listToXml(contacts: List[Contact]): List[Node] = contacts match { | |
case Nil => Nil | |
case c :: cs => | |
val contactXml = | |
<contact> | |
<name>{ c.name }</name> | |
<email>{ c.email }</email> | |
</contact> | |
contactXml :: listToXml(cs) | |
} | |
} |
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def optionMap[A, B](f: A => B)(maybeA: Option[A]): Option[B] = maybeA match { | |
case None => None | |
case Some(a) => Some(f(a)) | |
} |
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def listAsJson = Action { | |
Ok(Json.toJson(listMap(Contacts.all)(toJson))) | |
} | |
def readAsJson(id: Long) = Action { | |
optionMap(Contacts.byId(id))(toJson) match { | |
case Some(json) => Ok(json) | |
case None => NotFound | |
} | |
} |
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def toXml(c: Contact): Node = | |
<contact> | |
<name>{ c.name }</name> | |
<email>{ c.email }</email> | |
</contact> | |
def toJson(c: Contact): JsObject = | |
Json.obj( | |
"name" -> c.name, | |
"email" -> c.email | |
) |
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val listToXml = listMap(toXml) _ | |
val listToJson = listMap(toJson) _ |
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