Perl | Implementing a Stack

Stack in Perl is a linear data structure that follows the LIFO (Last In First Out) or FILO (First In Last Out) order.
In simpler terms, a stack is an array in which insertion and deletion takes place at only one end called the top of the stack.
Pushing is the process of insertion of elements into a stack.
Popping is the process of removal of topmost element of a stack.   Creating a stack in Perl is rather simple. All we need to do is declare an array.
The stack could be empty, as follows:

@stack;

Or it could be initialized:

@stack = (1, 2, 3);

  Pushing can be done using either the push() function or the splice() function.

• Pushing using push():

  Syntax: push(@stack, list); Parameters:

  • @stack - The stack on which push is to be performed.
  • list - The elements to be pushed into a stack. These elements might be scalar, array, hash or any combination of these.

  Example:
  Output:

  Original Stack: 1 2 3
  Updated Stack: 1 2 3 scalar a r r a y Geeks 10 for Geeks 20
  

• Pushing using splice():

  Syntax: splice(@stack, scalar(@stack), 0, list); Parameters:

  • splice() function appends the 'list' at the end of @stack.
  • THe 'list' could be a scalar, an array or a hash.

  Example:
  Output:

  Original Stack: 1 2 3
  Updated Stack: 1 2 3 scalar a r r a y Geeks 10 for Geeks 20
  

  Popping can be done using either the pop() function or the splice() function.

• Popping using pop():

  Syntax: $popped_element = pop(@stack); Parameters:

  • pop() function returns the popped element.
  • $popped_element contains the element popped from the stack.

  Example:
  Output:

  Original Stack: 1 2 3
  Popped element: 3
  Updated Stack: 1 2
  

  • If the stack is empty, undef is returned. undef is analogous to NULL in Java and None in Python. However, no error is raised.
  Example:
  Output:

  Popped element: 
  

• Popping using splice()::

  Syntax: $popped_element=splice(@stack, -1); Parameters:

  • splice() function removes the last element of the stack and returns it.
  • $popped_element stores the returned value.

  Example:
  Output:

  Original Stack: 1 2 3
  Popped element: 3
  Updated Stack: 1 2
  

  • An error is raised, if the stack is empty. The following code raises an error:
  Runtime Error:

  Useless use of a variable in void context at /home/59c7c19979aa9e46564cd145d5fe5601.pl line 6. Modification of non-creatable array value attempted, subscript -1 at /home/59c7c19979aa9e46564cd145d5fe5601.pl line 10.