Haskell
Haskell is a purely functional, statically typed programming language known for its strong emphasis on mathematical foundations, lazy evaluation, and type safety. It is widely used in academia, research, and industries requiring high reliability, such as finance and telecommunications, due to its expressive type system and ability to prevent runtime errors.
Developers should learn Haskell when working on projects that demand high correctness, such as financial systems, compilers, or formal verification tools, as its pure functional nature and advanced type features reduce bugs. It is also valuable for exploring functional programming paradigms, which can improve code quality in other languages, and for tasks involving complex data transformations or concurrency without side effects.