/ˈhæskəl/
noun … “Purely functional language for declarative computation.”
Haskell is a statically typed, purely Functional Programming language known for strong type inference, lazy evaluation, and immutability. Unlike imperative languages, Haskell emphasizes writing programs as expressions and function compositions, avoiding mutable state and side effects. Its type system, including algebraic data types and pattern matching, enables robust compile-time verification and expressive abstractions.
Key characteristics of Haskell include:
- Pure functions: every function produces the same output for given inputs without side effects.
- Lazy evaluation: expressions are evaluated only when needed, enabling infinite data structures and efficient computation.
- Strong static typing: the compiler ensures type correctness while often inferring types automatically.
- Immutability: all data structures are immutable by default, reducing concurrency issues.
- Rich abstractions: monads, functors, and higher-order functions provide composable building blocks for complex operations.
Workflow example: In Haskell, developers often define data pipelines as sequences of function compositions. For instance, mapping a transformation over a list and filtering results can be done in a single declarative expression without modifying the original list.
-- Compute squares of even numbers
let numbers = [1, 2, 3, 4, 5]
let squaredEven = map (^2) (filter even numbers)
print squaredEven -- Output: [4,16]This demonstrates lazy evaluation and function composition: filter selects elements, and map applies a transformation, producing a new list without changing the original.
Conceptually, Haskell is like a recipe book where ingredients (data) are never altered; instead, each function produces a new dish (result) from the inputs. This approach makes reasoning about programs, testing, and parallel execution predictable and safe.
See Functional Programming, Scala, Type System, Monads.