I'd suggest taking a look at Coq if you want something more pure than Haskell. I'll warn you that this comes with some degree of added sophistication! Coq is no

I'd suggest taking a look at Coq if you want something more pure than Haskell. I'll warn you that this comes with some degree of added sophistication! Coq is not just a programming language but instead a proof system which can be used to verify programs as correct (not just unit tested) and then extract the skeletal, underlying program as OCaml, Haskell, or Scheme code. http://adam.chlipala.net/cpdt/ http://adam.chlipala.net/cpdt/ True purity actually doesn't look much like Go at all. Instead, it means that every expression literally can be evaluated and replaced with its value in a completely arbitrary order. This massively simplifies the meaning of a language and opens it up to bear much more structure (such as that of a mathematical proof).