Pure Functions - Haskell Typing CST Test
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Pure Functions — Haskell Code
Demonstrates Haskell's pure functions, pattern matching, and list operations.
-- Define a custom data type
data Shape = Circle Float | Rectangle Float Float
-- Calculate area using pattern matching
area :: Shape -> Float
area (Circle r) = pi * r * r
area (Rectangle w h) = w * h
-- Higher-order functions
quicksort :: (Ord a) => [a] -> [a]
quicksort [] = []
quicksort (x:xs) =
let smaller = quicksort [a | a <- xs, a <= x]
bigger = quicksort [a | a <- xs, a > x]
in smaller ++ [x] ++ bigger
-- List operations
fibonacci :: [Integer]
fibonacci = 0 : 1 : zipWith (+) fibonacci (tail fibonacci)
-- Main function
main :: IO ()
main = do
let shapes = [Circle 5.0, Rectangle 3.0 4.0, Circle 2.5]
let areas = map area shapes
putStrLn $ "Areas: " ++ show areas
putStrLn $ "First 10 fibonacci: " ++ show (take 10 fibonacci)
putStrLn $ "Sorted [3,1,4,1,5,9]: " ++ show (quicksort [3,1,4,1,5,9])Haskell Language Guide
Haskell is a purely functional, statically typed programming language known for immutability, strong type inference, mathematical precision, and high reliability. It is widely used in finance, compilers, research, distributed systems, and correctness-critical software.
Primary Use Cases
- ▸Pure functional application development
- ▸Distributed systems
- ▸Financial trading engines
- ▸Compilers & language tooling
- ▸Formal verification
- ▸Research & algorithm modeling
- ▸Simulation & high-assurance software
Notable Features
- ▸Purely functional programming
- ▸Lazy evaluation model
- ▸Advanced type system (typeclasses, GADTs, HKTs)
- ▸Strong type inference
- ▸Immutability-first design
- ▸Concise mathematical syntax
Origin & Creator
Developed by a committee of academics in 1990 led by Simon Peyton Jones, Paul Hudak, and Philip Wadler to create a standard pure functional language.
Industrial Note
Haskell excels in domains needing mathematical correctness, high-assurance code, compiler/tooling development, fintech trading systems, distributed ledgers, blockchain research, and formally verifiable system design.
Quick Explain
- ▸Haskell is purely functional - everything is an expression without mutable state.
- ▸It features strong static typing powered by an advanced type system.
- ▸Used for reliable backend systems, research, compilers, finance, and high-assurance software.
Core Features
- ▸Purity and referential transparency
- ▸Static strong typing
- ▸Lazy evaluation
- ▸Typeclasses for polymorphism
- ▸Algebraic data types
- ▸Pattern matching
Learning Path
- ▸Learn functional thinking
- ▸Master types & typeclasses
- ▸Learn monads & effects
- ▸Work with libraries & frameworks
- ▸Build real projects
Practical Examples
- ▸Functional utilities
- ▸Basic web server
- ▸Concurrent pipeline
- ▸Parser combinator
- ▸Compiler-style transformations
Comparisons
- ▸Safer and more mathematical than Python
- ▸More advanced type system than Java
- ▸Stronger safety guarantees than JavaScript
- ▸Slower ecosystem growth than Rust
Strengths
- ▸Extremely safe and reliable
- ▸Concise, expressive code
- ▸Powerful type system
- ▸Great for concurrency
- ▸Excellent for correctness-critical work
Limitations
- ▸Steeper learning curve
- ▸Smaller industry adoption
- ▸Slower prototyping than Python/JS
- ▸Harder onboarding for teams
- ▸Limited mobile ecosystem
When NOT to Use
- ▸Mobile apps
- ▸Rapid MVP prototyping
- ▸Teams without FP experience
- ▸Large frontend development
Cheat Sheet
- ▸Function: f x = x + 1
- ▸List: [1,2,3]
- ▸Map: map (+1) list
- ▸Monad: do-notation sequencing
- ▸Typeclass: class Eq a where ...
FAQ
- ▸Is Haskell hard?
- ▸It has a learning curve but becomes extremely powerful.
- ▸Is Haskell good for production?
- ▸Yes-used in fintech, compilers, and correctness-critical systems.
- ▸Is Haskell fast?
- ▸With optimization, Haskell can be very fast, comparable to C-like languages.
- ▸Do companies use Haskell?
- ▸Yes, especially in finance, research, compilers, and blockchain.
30-Day Skill Plan
- ▸Week 1: Pure functions & types
- ▸Week 2: Monads & typeclasses
- ▸Week 3: I/O & concurrency
- ▸Week 4: Real-world backend
Final Summary
- ▸Haskell is a purely functional language built for reliability and mathematical correctness.
- ▸It excels in high-assurance systems, compilers, research, and fintech.
- ▸Its type system, purity, and laziness make it uniquely powerful.
- ▸Though harder to learn, it rewards developers with unmatched safety and expressiveness.
Project Structure
- ▸src/ modules
- ▸package.yaml or cabal file
- ▸stack.yaml
- ▸tests/ folder
- ▸Main.hs entry point
Monetization
- ▸Fintech engineering
- ▸Compiler/PL engineering
- ▸Backend development
- ▸High-assurance consulting
Productivity Tips
- ▸Start in ghci REPL
- ▸Use pure functions first
- ▸Add types early
- ▸Profile laziness
Basic Concepts
- ▸Immutability
- ▸Expressions over statements
- ▸Functions and purity
- ▸Type system & typeclasses
- ▸Pattern matching
- ▸Monads & functors
Official Docs
- ▸Haskell Report
- ▸GHC User Guide
- ▸Haskell Wiki