Compare the signatures of map
and flatMap
and coflatMap
:
Compare the signatures of map
and flatMap
and coflatMap
:
def map[A, B](fa: Id[A])(f: A => B): Id[B] def flatMap[A, B](fa: Id[A])(f: A => Id[B]): Id[B] def coflatMap[A, B](a: Id[A])(f: Id[A] => B): Id[B]
You'll notice that in the flatMap signature, since Id[B]
is the same
as B
for all B, we can rewrite the type of the f
parameter to be
A => B
instead of A => Id[B]
, and this makes the signatures of the
two functions the same, and, in fact, they can have the same
implementation, meaning that for Id
, flatMap
is also just function
application:
import cats.Monad val one: Int = 1 Monad[Id].map(one)(_ + 1) Monad[Id].flatMap(one)(_ + 1)
We can freely compare values of Id[T]
with unadorned
values of type T
.
Using this type declaration, we can treat our Id type constructor as a
Monad
and as a Comonad
.
Using this type declaration, we can treat our Id type constructor as a
Monad
and as a Comonad
. The pure
method, which has type A => Id[A]
just becomes the identity
function. The map
method from Functor
just becomes function
application:
import cats.Functor val one: Int = 1 Functor[Id].map(one)(_ + 1)
This method has been deprecated in favor of macro assertion and will be removed in a future version of ScalaTest. If you need this, please copy the source code into your own trait instead.
This method has been deprecated in favor of macro assertion and will be removed in a future version of ScalaTest. If you need this, please copy the source code into your own trait instead.
This method has been deprecated in favor of macro assumption and will be removed in a future version of ScalaTest. If you need this, please copy the source code into your own trait instead.
This method has been deprecated in favor of macro assumption and will be removed in a future version of ScalaTest. If you need this, please copy the source code into your own trait instead.
Please use 'an [Exception] should be thrownBy { ... }' syntax instead
This expect method has been deprecated. Please replace all invocations of expect with an identical invocation of assertResult instead.
This expect method has been deprecated. Please replace all invocations of expect with an identical invocation of assertResult instead.
This expectResult method has been deprecated. Please replace all invocations of expectResult with an identical invocation of assertResult instead.
This expectResult method has been deprecated. Please replace all invocations of expectResult with an identical invocation of assertResult instead.
The identity monad can be seen as the ambient monad that encodes the effect of having no effect. It is ambient in the sense that plain pure values are values of
Id
.It is encoded as:
type Id[A] = A
That is to say that the type Id[A] is just a synonym for A. We can freely treat values of type
A
as values of typeId[A]
, and vice-versa.