The List

A list is a container with a collection of items of the same type. It can either be empty or contain one or more items.

Constructing the list

Empty list

Constructing an empty list block, simply remove all members from the input block toolbox [⚙].

Fig. 1: The empty list block

SMLScala

[]

List()

Fig. 2: Connecting the empty list block to the variable block

SMLScala

val list_constructor = []

val list_constructor = List()

Non-empty list

The inhabitants of the list can be added or removed using the input block toolbox.

Fig. 3: Constructing the non-empty list block

SMLScala

["my name ", "is ", "MNL"]

List("my name ", "is ", "MNL")

Fig. 4: Connecting the non-empty list block to the variable block

SMLScala

val list_constructor = ["my name ", "is ", "MNL"]

val list_constructor = List("my name ", "is ", "MNL")

Operator

is empty

To check whether the list is empty, return true when it is empty; otherwise, return false.

Fig. 5: The is-empty block operator with the empty list block

SMLScala

val list_constructor = null([])

val list_constructor = List().isEmpty

Fig. 6: The is-empty block operator with the non-empty list block

SMLScala

val list_constructor = null([])

val list_constructor = List().isEmpty

head

Retrieve the first inhabitant from the list.

Fig. 7: The head list operator block

SMLScala

hd(["My name ", "is ", "MNL"])

List("My name ", "is ", "MNL").head

tail

Obtain the inhabitants of the list, starting from the second inhabitant to the last one.

Fig. 8: The tail list operator block

SMLScala

tl(["My name ", "is ", "MNL"])

List("My name ", "is ", "MNL").tail

append

Insert a new inhabitant into the list and put it into the first position.

Fig. 9: The append list operator block

SMLScala

("Hello, " :: ["My name ", "is ", "MNL"])

("Hello, " :: List("My name ", "is ", "MNL"))

Fig. 10: The append a new inhabitant and bind to a variable block.

SMLScala

val my_name_is_mnl = ["My name", "is", "MNL"]
val hello = ("Hello, " :: my_name_is_mnl)

val my_name_is_mnl = List("My name", "is", "MNL")
val hello = ("Hello, " :: my_name_is_mnl)

Example

Sum

Fig. 11: The head list operator block

SMLScala

fun sum_list (list_a) = if null(list_a)
  then
    0
  else
    (hd(list_a)  + sum_list(tl(list_a)))

val sum_list_application = sum_list([17, 2, 200, 4])

def sum_list (list_a: List[Float]) : Float = if (list_a.isEmpty)
  then
    0
  else
    ((list_a.head)  + sum_list((list_a.tail)))

val sum_list_application = sum_list(List(17, 2, 200, 4))