How deeply does Learn Haskell by Example cover union type?

Defines constructors and demonstrates pattern matching through a complete padding function, without descending into runtime internals.

Union type

As explained in Learn Haskell by Example

A sum type is a data type whose value is one of several alternative constructors, with only one constructor choice present at a time.

A union type, also called a sum type or tagged union, represents one choice from several named alternatives. In Haskell, define the alternatives with data constructors, then pattern match on the selected constructor. section 4.3.1

Listing 4.7 Simple type for distinguishing left from right padding

data PadMode = PadLeft | PadRight

A minimal PadMode type distinguishes left padding from right padding. section 4.3.1

Choosing a padding direction

Use the selected constructor to control the implementation: pad PadLeft 10 "Pad me!" produces " Pad me!", while pad PadRight 10 "Pad me!" produces "Pad me! ". A case expression selects the matching branch. section 4.3.1

Union types provide three practical design benefits:

Name each permitted alternative explicitly, such as PadLeft and PadRight. section 4.3.1
Keep alternatives mutually exclusive: one constructor is present at a time. section 4.3.1
Make each alternative visible to pattern matching and case expressions. section 4.3.1

How Learn Haskell by Example covers it

liveBook manning.com

Read Learn Haskell by Example on liveBook Get the book at manning.com

Also explained in

liveBook manning.com

Essential TypeScript 5, Third EditionA union type is a TypeScript type that allows a value to conform to any one of multiple constituent types and exposes only members shared by those types.
liveBook manning.com

Pro Angular 16A union type is a TypeScript type that permits a value to belong to one of several specified types.
liveBook manning.com

F# in Action: A Revised Edition of Get Programming with F#A discriminated union is an F# type whose values are selected from a fixed set of named cases, each potentially carrying different data.
liveBook manning.com

Functional Design and Architecture: Examples in HaskellA sum type represents a value that can be one of several alternative constructors or variants.
liveBook manning.com

Kafka Streams in Action, Second EditionA union type is a construct whose value or field may conform to one of several specified types.
liveBook manning.com

React in DepthA discriminated union is a TypeScript union type whose alternatives are distinguished by a shared property with distinct literal values.
liveBook manning.com

Modern C, Third EditionA C union is a user-defined type whose members occupy overlapping storage and are represented by the same memory location.
liveBook manning.com

Modern CA union is a C type whose members share the same memory location, so different members overlay one another.
liveBook manning.com

Python How-ToA union type specifies that a value may belong to one of several permitted data types.

Compare how 10 books explain union type →

Related concepts

result typeincludes · A type that represents an operation’s outcome as either a successful value or a failure value.
System.Text.Jsoncontrasts with · System.Text.Json is a .NET library providing APIs for serializing, deserializing, reading, writing, and processing JSON data.
single-case discriminated unionincludes · A single-case discriminated union is a discriminated union with exactly one named case, typically used to create a distinct domain-specific type around another value.
parameterized typekind of · A parameterized type is a type definition or constructor that takes one or more type parameters to produce a specialized or concrete type.
algebraic data typekind of · An algebraic data type is a composite type whose values are formed from product structures, finite alternatives, or both through type constructors.
in-memory formatuses · An in-memory format is the structure and representation used to store data or values in computer memory during program execution.

This explainer was generated by Manning's knowledge graph from the text of Learn Haskell by Example. The section links point to the parts of the book it draws on.