John Backus's seminal paper, "Can Programming be Liberated from the von Neumann Style? A Functional Style and its Algebra of Programs" argues for this really we

John Backus's seminal paper, "Can Programming be Liberated from the von Neumann Style? A Functional Style and its Algebra of Programs" argues for this really well. http://worrydream.com/refs/Backus-CanProgrammingBeLiberated.pdf http://worrydream.com/refs/Backus-CanProgrammingBeLiberated.... Declarativity, compositionality, and referential transparency are all part of how he defines it. But he also takes a moment to contrast his idea of functional programming with a "lambda-calculus based system" (read: lisp), and one of the things he specifically criticizes is that, in those systems, functions aren't automatically curried. (His actual wording was that they are allowed to take multiple arguments, but the meaning is roughly the same.) The gist of the argument is that requiring functions to only be unary limits the number of operations you need to compose functions, which ultimately keeps the system simpler and easier to understand. He compares limiting function arity in functional programming to limiting the number of available control structures in structured programming: Strictly speaking, you lose some expressivity, but it's justified by all the other things you get in return.