In Haskell, every expression possesses a type that is established during the compilation process. The types involved in function applications must align correctly; otherwise, the compiler will reject the program. This strict type system not only serves as a guarantee of correctness but also functions as a language for articulating the construction of programs. Each function in Haskell adheres to the principles of mathematical functions, meaning they are "pure" in nature. Even when dealing with side-effecting IO operations, they merely outline actions to be taken, generated by pure functions. Haskell does not utilize statements or instructions; instead, it relies solely on expressions that cannot alter variables, whether local or global, nor can they manipulate states such as time or randomness. While it is not necessary to specify every type in a Haskell program, the types can be inferred through a process of bidirectional unification. Still, programmers have the option to explicitly define types as needed or request the compiler to generate them for reference, thereby enriching documentation and enhancing clarity. This flexibility allows Haskell developers to strike a balance between type safety and ease of use.