Philip Wadler is a computer scientist known for his work on functional programming languages and type systems. His own homepage records that he was a principal designer of Haskell, a Professor of Theoretical Computer Science at the University of Edinburgh, and an ACM Fellow, and that his research spans type systems, functional programming, and the Curry-Howard correspondence.
Wadler is closely associated with bringing monads into practical functional programming. His papers on the subject describe how monads “provide a convenient framework for simulating effects found in other languages, such as global state, exception handling, output, or non-determinism,” which became the standard way Haskell structures effectful code while keeping functions pure.
Beyond monads, Wadler contributed to the design of Haskell’s type classes and later worked on adding generics to Java. He is also a prominent advocate of the idea that propositions correspond to types and proofs correspond to programs, a theme he develops under the banner of the Curry-Howard correspondence, linking mathematical logic directly to programming.