Why Object Nil can't create?
0
Having the error:
Object creation impossible, since member node: Option[(A, MyModule.List[A])] in MyModule.List is not defined
sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
abstract class Cons[+A](head: A, tail: List[A]) extends List[A]
object Nil extends List[Nothing]
object List {
def empty[A] = new List[A] { def node = None }
def cons[A](head: A, tail: List[A]) = new List[A] { def node = Some((head, tail)) }
def apply[A](as: A*):List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))In this case, how to implement?
I wonder what functions should be put in trait and what functions should be put in Company Object.
scala
asked Nov 15 '18 at 3:28
ArobtArobt
114
add a comment |
0
Having the error:
Object creation impossible, since member node: Option[(A, MyModule.List[A])] in MyModule.List is not defined
sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
abstract class Cons[+A](head: A, tail: List[A]) extends List[A]
object Nil extends List[Nothing]
object List {
def empty[A] = new List[A] { def node = None }
def cons[A](head: A, tail: List[A]) = new List[A] { def node = Some((head, tail)) }
def apply[A](as: A*):List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))In this case, how to implement?
I wonder what functions should be put in trait and what functions should be put in Company Object.
scala
asked Nov 15 '18 at 3:28
ArobtArobt
114
add a comment |
0
0
0
Having the error:
Object creation impossible, since member node: Option[(A, MyModule.List[A])] in MyModule.List is not defined
sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
abstract class Cons[+A](head: A, tail: List[A]) extends List[A]
object Nil extends List[Nothing]
object List {
def empty[A] = new List[A] { def node = None }
def cons[A](head: A, tail: List[A]) = new List[A] { def node = Some((head, tail)) }
def apply[A](as: A*):List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))In this case, how to implement?
I wonder what functions should be put in trait and what functions should be put in Company Object.
scala
asked Nov 15 '18 at 3:28
ArobtArobt
114
Having the error:
Object creation impossible, since member node: Option[(A, MyModule.List[A])] in MyModule.List is not defined
sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
abstract class Cons[+A](head: A, tail: List[A]) extends List[A]
object Nil extends List[Nothing]
object List {
def empty[A] = new List[A] { def node = None }
def cons[A](head: A, tail: List[A]) = new List[A] { def node = Some((head, tail)) }
def apply[A](as: A*):List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))In this case, how to implement?
I wonder what functions should be put in trait and what functions should be put in Company Object.
sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
abstract class Cons[+A](head: A, tail: List[A]) extends List[A]
object Nil extends List[Nothing]
object List {
def empty[A] = new List[A] { def node = None }
def cons[A](head: A, tail: List[A]) = new List[A] { def node = Some((head, tail)) }
def apply[A](as: A*):List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
abstract class Cons[+A](head: A, tail: List[A]) extends List[A]
object Nil extends List[Nothing]
object List {
def empty[A] = new List[A] { def node = None }
def cons[A](head: A, tail: List[A]) = new List[A] { def node = Some((head, tail)) }
def apply[A](as: A*):List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))scala
scala
asked Nov 15 '18 at 3:28
ArobtArobt
114
asked Nov 15 '18 at 3:28
ArobtArobt
114
edited Nov 15 '18 at 8:57
Arobt
asked Nov 15 '18 at 3:28
ArobtArobt
114
asked Nov 15 '18 at 3:28
ArobtArobt
114
asked Nov 15 '18 at 3:28
ArobtArobt
114
114
add a comment |
add a comment |
1 Answer
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Here is correct implementation:
sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
case class Cons[+A](head: A, tail: List[A]) extends List[A] {
override def node: Option[(A, List[A])] = Some((head, tail))
}
object Nil extends List[Nothing] {
override def node: Option[(Nothing, List[Nothing])] = None
}
object List {
def empty[A] = new List[A] {
def node = None
}
def cons[A](head: A, tail: List[A]) = new List[A] {
def node = Some((head, tail))
}
def apply[A](as: A*): List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))
}
}
I see few problems here:
1) You have two implementation of cons
you can implement cons method simpler:
def cons[A](head: A, tail: List[A]) = Cons(head, tail)
2) Same with empty
def empty[A] = Nil
answered Nov 15 '18 at 3:46
talextalex
10.6k1547
Yes, Cons and Empty implementations are duplicated. In the object List, no new List is needed, only the new Cons and Nil are needed.Just like you added.
– Arobt
Nov 15 '18 at 8:45
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
0
Here is correct implementation:
sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
case class Cons[+A](head: A, tail: List[A]) extends List[A] {
override def node: Option[(A, List[A])] = Some((head, tail))
}
object Nil extends List[Nothing] {
override def node: Option[(Nothing, List[Nothing])] = None
}
object List {
def empty[A] = new List[A] {
def node = None
}
def cons[A](head: A, tail: List[A]) = new List[A] {
def node = Some((head, tail))
}
def apply[A](as: A*): List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))
}
}
I see few problems here:
1) You have two implementation of cons
you can implement cons method simpler:
def cons[A](head: A, tail: List[A]) = Cons(head, tail)
2) Same with empty
def empty[A] = Nil
answered Nov 15 '18 at 3:46
talextalex
10.6k1547
Yes, Cons and Empty implementations are duplicated. In the object List, no new List is needed, only the new Cons and Nil are needed.Just like you added.
– Arobt
Nov 15 '18 at 8:45
add a comment |
0
Here is correct implementation:
sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
case class Cons[+A](head: A, tail: List[A]) extends List[A] {
override def node: Option[(A, List[A])] = Some((head, tail))
}
object Nil extends List[Nothing] {
override def node: Option[(Nothing, List[Nothing])] = None
}
object List {
def empty[A] = new List[A] {
def node = None
}
def cons[A](head: A, tail: List[A]) = new List[A] {
def node = Some((head, tail))
}
def apply[A](as: A*): List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))
}
}
I see few problems here:
1) You have two implementation of cons
you can implement cons method simpler:
def cons[A](head: A, tail: List[A]) = Cons(head, tail)
2) Same with empty
def empty[A] = Nil
answered Nov 15 '18 at 3:46
talextalex
10.6k1547
Yes, Cons and Empty implementations are duplicated. In the object List, no new List is needed, only the new Cons and Nil are needed.Just like you added.
– Arobt
Nov 15 '18 at 8:45
add a comment |
0
0
0
Here is correct implementation:
sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
case class Cons[+A](head: A, tail: List[A]) extends List[A] {
override def node: Option[(A, List[A])] = Some((head, tail))
}
object Nil extends List[Nothing] {
override def node: Option[(Nothing, List[Nothing])] = None
}
object List {
def empty[A] = new List[A] {
def node = None
}
def cons[A](head: A, tail: List[A]) = new List[A] {
def node = Some((head, tail))
}
def apply[A](as: A*): List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))
}
}
I see few problems here:
1) You have two implementation of cons
you can implement cons method simpler:
def cons[A](head: A, tail: List[A]) = Cons(head, tail)
2) Same with empty
def empty[A] = Nil
answered Nov 15 '18 at 3:46
talextalex
10.6k1547
Here is correct implementation:
sealed trait List[+A] {
def node: Option[(A, List[A])]
def isEmpty = node.isEmpty
}
case class Cons[+A](head: A, tail: List[A]) extends List[A] {
override def node: Option[(A, List[A])] = Some((head, tail))
}
object Nil extends List[Nothing] {
override def node: Option[(Nothing, List[Nothing])] = None
}
object List {
def empty[A] = new List[A] {
def node = None
}
def cons[A](head: A, tail: List[A]) = new List[A] {
def node = Some((head, tail))
}
def apply[A](as: A*): List[A] = {
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))
}
}
I see few problems here:
1) You have two implementation of cons
you can implement cons method simpler:
def cons[A](head: A, tail: List[A]) = Cons(head, tail)
2) Same with empty
def empty[A] = Nil
answered Nov 15 '18 at 3:46
talextalex
10.6k1547
answered Nov 15 '18 at 3:46
talextalex
10.6k1547
answered Nov 15 '18 at 3:46
talextalex
10.6k1547
answered Nov 15 '18 at 3:46
talextalex
10.6k1547
10.6k1547
Yes, Cons and Empty implementations are duplicated. In the object List, no new List is needed, only the new Cons and Nil are needed.Just like you added.
– Arobt
Nov 15 '18 at 8:45
add a comment |
Yes, Cons and Empty implementations are duplicated. In the object List, no new List is needed, only the new Cons and Nil are needed.Just like you added.
– Arobt
Nov 15 '18 at 8:45
Yes, Cons and Empty implementations are duplicated. In the object List, no new List is needed, only the new Cons and Nil are needed.Just like you added.
– Arobt
Nov 15 '18 at 8:45
Yes, Cons and Empty implementations are duplicated. In the object List, no new List is needed, only the new Cons and Nil are needed.Just like you added.
– Arobt
Nov 15 '18 at 8:45
add a comment |
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