Why and How Functional Programming By Anupam Jain 

About Me •Organiser of FPNCR meetup •Programming professionally for over 12 years •Mostly Javascript and Haskell •Built large production systems with Haskell •Some FOSS libraries - •Web UIs - (https://github.com/ajnsit/concur) •Servers - (https://github.com/ajnsit/wai-routes) 

What is Functional Programming •Functions Exist! •Functions are not Procedures. •Input and Output •First class 

What is Functional Programming •Functional •Declarative • Pure • Immutable • Statically Typed • Algebraic Data Types • Lazy • Concurrent • …… 

What is Functional Programming •Functional •Declarative • Pure • Immutable • Statically Typed • Algebraic Data Types • Lazy • Concurrent • …… Functions are the mode of abstraction 

What is Functional Programming •Functional •Declarative •Pure • Immutable • Statically Typed • Algebraic Data Types • Lazy • Concurrent • …… No sequence of steps 

What is Functional Programming •Functional •Declarative •Pure • Immutable • Statically Typed • Algebraic Data Types • Lazy • Concurrent • …… No side effects 

What is Functional Programming •Functional •Declarative • Pure •Immutable • Statically Typed • Algebraic Data Types • Lazy • Concurrent • …… No assignments 

What is Functional Programming •Functional •Declarative • Pure • Immutable •Statically Typed • Algebraic Data Types • Lazy • Concurrent • …… Potentially invalid programs are not compiled 

What is Functional Programming •Functional •Declarative • Pure • Immutable • Statically Typed •Algebraic Data Types • Lazy • Concurrent • …… User defined data types are sums of products 

What is Functional Programming •Functional •Declarative •Pure • Immutable • Statically Typed • Algebraic Data Types •Lazy • Concurrent • …… Order of evaluation is unknown 

The Sweet Spot Productivity Quality Resilience FP 

Productivity • Steep learning curve. But.. • Abstraction • Types • Isolation • APIs - Immutability, Laziness, Composition 

Productivity • Very few FP practitioners. But… • Supply vs Demand • High Quality Talent Pool • High Employee Satisfaction • Remote • Training 

Quality • Excellent Abstractions Pre-cooked for you • Excellent libraries for many things. Such as async programming. 

Quality • Static types hinder quick scripts. But.. • Easy Refactoring, checked at compile time • Slight Hyperbole - “If it compiles it works” • Reality - “Refactor without fear” • Let the computer help you help yourself • All this implies - Low Tech Debt 

Resilience • Forced to Manage Complexity • No Hidden State or Effects • Large class of bugs caught at Compile Time. • Great Refactoring Story. 

Functions • Functions exist! • Local and anonymous function definitions. • Higher order functions • First class functions 

Other things • Do notation. General purpose. • Alternative is a natural fit for many domains like parsing, gui construction. You can define many algorithmic functions on top like optional, many, foldMap etc. Almost forms a DSL. • Advanced techniques • Free Monads • Monad Transformers • Lens, Conduit, Pipes 

Via Haskell • Haskell Syntax • Haskell Semantics 

FPNCR •The Delhi/NCR Haskell and other Functional Programming Languages Meetup Group •https://www.meetup.com/DelhiNCR-Haskell-And- Functional-Programming-Languages-Group •Github- https://github.com/fpncr •Mailing List - https://groups.google.com/forum/#!forum/ fpncr •Slack - https://functionalprogramming.slack.com - #FPNCR