Tail

As explained in Functional Programming in Scala, Second Edition

tail is a list operation that returns all elements except the first, failing when applied to Nil.

tail is a list operation that returns every element after the first. For a nonempty list val mylist = Cons(x, xs), tail returns xs without changing mylist. Because the list is immutable, the result can reuse the existing structure rather than copy it. section 3.3

Removing the first element

Given Cons(1, Cons(2, Nil)), tail returns Cons(2, Nil). Applying tail to Nil fails; the exercise permits using sys.error("message") for that case. The operation takes constant time because it returns the stored tail directly. section 3.3 section 3.1

Implement tail against the custom list definition:

• Handle Cons by returning its tail field. section 3.3
• Handle Nil by raising an error rather than returning a list. section 3.3
• Use the defined List and Nil types, not Scala’s built-in versions. section 3.3

Figure 3.3 Data sharing of lists

Use the data-sharing figure to see how tail preserves the original list while returning a reference to its remaining structure. section 3.3

How Functional Programming in Scala, Second Edition covers it

How deep it goes

Explains constant-time removal and the Nil failure case, but defers alternative error-handling techniques.

Examples

Uses Cons(x, xs), mylist, and the shared structure illustrated by Figure 3.3.

What it assumes

Assumes familiarity with Cons and Nil, while teaching immutable removal through structural sharing.

What you can do after

Build it from scratch as a constant-time operation over the custom Scala List type.

How it connects

Connects tail to singly linked lists, immutable data structures, persistent data structures, and data sharing.

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Also explained in

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  Grokking Data StructuresThe tail is the reference or position identifying the last node of a linked list.
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  Elixir in Action, Third EditionThe tail of a list is the remainder following its first element in a head-and-tail representation.

Compare how 3 books explain tail →

Related concepts

• referenceconfigured by · A reference is an indirect value or relationship that identifies or provides access to another value, object, resource, or source.
• listimplements · A list is an ordered collection of elements arranged in a sequence.
• tuplepart of · A tuple is a finite, ordered collection of elements treated as a single composite value or record.
• linked listpart of · An ordered sequence of elements stored in separate nodes connected by links or references rather than in one contiguous storage region.
• doubly linked listused by · A doubly linked list is a linked sequence in which each node has references to both its predecessor and successor.
• pattern matchingproduced by · Pattern matching is the process of comparing data or values with specified or learned patterns to identify correspondence, conformity, or a matching case.

This explainer was generated by Manning's knowledge graph from the text of Functional Programming in Scala, Second Edition. The section links point to the parts of the book it draws on.