book

Functional Programming with C#

by Simon J. Painter

September 2023

Intermediate to advanced

325 pages

7h 45m

English

O'Reilly Media, Inc.

Book available

Read now

Unlock full access

Who Should Read This Book?Why I Wrote This BookNavigating This BookConventions Used in This BookUsing Code ExamplesO’Reilly Online LearningHow to Contact UsAcknowledgments
What Is Functional Programming?Is It a Language, an API, or What?The Properties of Functional ProgrammingBaking CakesAn Imperative CakeA Declarative CakeWhere Does Functional Programming Come From?Who Else Does Functional Programming?Pure Functional LanguagesIs It Worth Learning a Pure Functional Language First?What About F#? Should I Be Learning F#?Multiparadigm LanguagesThe Benefits of Functional ProgrammingConciseTestableRobustPredictableBetter Support for ConcurrencyReduced Code NoiseThe Best Places to Use Functional ProgrammingWhere You Should Consider Using Other ParadigmsHow Far Can We Take This? Monads Actually, Don’t Worry About This YetSummary
Getting StartedWriting Your First Functional CodeA Nonfunctional Film QueryA Functional Film QueryFocusing on Results-Oriented ProgrammingUnderstanding EnumerablesPreferring Expressions to StatementsThe Humble SelectMany to One: The Subtle Art of AggregationCustomized Iteration BehaviorMaking Your Code ImmutablePutting It All Together: A Complete Functional FlowTaking It Further: Develop Your Functional SkillsSummary
TuplesPattern MatchingProcedural Bank AccountsPattern Matching in C# 7Pattern Matching in C# 8Pattern Matching in C# 9Pattern Matching in C# 10Pattern Matching in C# 11Read-Only StructsInit-Only SettersRecord TypesNullable Reference TypesThe FutureDiscriminated UnionsActive PatternsSummary
It’s Time to Get Func-yFuncs in EnumerablesA Super-Simple ValidatorPattern Matching for Old Versions of C#Make Dictionaries More UsefulParsing ValuesCustom EnumerationsQuery Adjacent ElementsIterate Until a Condition Is MetSummary
A Problem ReportThunksChaining FunctionsFork CombinatorAlt CombinatorComposeTransduceTapTry/CatchHandling NullsUpdate an EnumerableSummary
Holiday TimeHolidays with Discriminated UnionsSchrödinger’s UnionNaming ConventionsDatabase LookupSending EmailConsole InputGeneric UnionsMaybeResultMaybe Versus ResultEitherSummary
Maybe, RevisitedMaybe and DebuggingMap() Versus Bind()Maybe and the PrimitivesMaybe and LoggingMaybe and AsyncNested MaybesThe LawsLeft Identity LawRight Identity LawAssociativity LawReaderStateMaybe a State?Examples You’re Already UsingEnumerableTaskOther StructuresA Worked ExampleSummary

Currying and Large FunctionsCurrying and Higher-Order FunctionsCurrying in .NETPartial ApplicationPartial Application in .NETSummary
RecursionTrampoliningCustom IteratorUnderstanding the Anatomy of an EnumeratorImplementing Custom EnumeratorsIndefinitely Looping EnumerablesUsing Indefinite IteratorsSummary
Bacon NumbersImplementing Memoization in C#Summary
Functional C# and PerformanceBaseline: An Imperative SolutionPerformance ResultsWhat Does All of This Mean?Functional C# Concerns and QuestionsHow Functional Should I Make My Codebase?How Should I Structure a Functional C# Solution?How Do I Share My Functional Methods Among Applications?Did You Order This Pizza?How Do I Convince My Teammates to Do This Too?Is It Worth Including F# Projects in My Solution?Will Functional Coding Solve All My Problems?Connery, Moore, or Craig?How Do I Think Through a Problem Functionally?What If There’s No Way to Make a Bit of Code as High-Performant as I’d Like with Functional-Style Code?Summary
OneOfLanguageExtOptionEitherMemoizationReaderStateLanguageExt Wrap-upFunctional.MaybeCSharpFunctionalExtensionsMaybeResultFluent AssertionsCSharpFunctionalExtensions Wrap-upThe F# Programming LanguageSummary
StoryTechnical DetailCreating the GameThe SolutionCommunicationsWant to Learn How to Play?The Inventory SetupThe Game LoopSummary
What Kind of Day Has It Been?Where Do I Go from Here?More Functional C#Learn F#Pure Functional LanguagesWhat About You?

Content preview from Functional Programming with C#

Part II. Into the Belly of the Functional

Hail, bold adventurer!

I see you’ve survived the first part of your journey. Now you can consider yourself promoted from functional apprentice to journeyman.¹ This next road is longer, twistier, and far stranger.

Be not afraid, though, because if you are open to it, wonders await you ahead. This is where we stop thinking entirely in terms of out-of-the-box C# and start looking a little more into functional theory.

I hope you aren’t expecting formal definitions, or talk on list theory, because you won’t find that here. I’m going to take you up the gentle slope, a step at a time—always with an eye to what’s actually useful to you in your daily coding.

Come along. The horses are getting restless. It’s time to saddle up!

¹ Journeyman is a historical job title from a less enlightened age, which I felt was too perfect here not to use. Please feel free to remove “man” and insert the correct term for yourself.