Lisp vs Haskell: which is better for pure functional design?

Haskell enforces functional purity at compile time through its static type system; Lisp does not enforce purity at all and leaves immutability and side-effect discipline to the programmer's own conventions. Haskell's type system, built on compiler-driven type inference since its 1990 release, is what makes that enforcement possible.

How do Lisp and Haskell handle purity and types?

What can Lisp offer a purity-minded design?

Lisp can be written in a purely functional style if the team disciplines itself, and its macro system lets a team build its own conventions for enforcing that style, such as naming rules or linting. Nothing in the language itself stops a function from mutating state or performing IO anywhere in the code.

What does Haskell guarantee that Lisp doesn't?

Haskell's compiler refuses to build code that mixes pure and impure logic without explicitly marking the impure parts through the IO type, and its default immutability means data cannot be silently changed after it is created. That guarantee holds regardless of who wrote the code or how careful they were.

Which one fits a project that needs enforced purity?

If pure functional design is a hard requirement rather than a preference, Haskell is the better fit because the compiler enforces it instead of relying on team discipline. Lisp remains a strong choice when a team wants functional style available as one tool among several rather than a fixed constraint on every function.