Tony Morris

It seems clear when you consider that an untyped Haskell would obviously not be pure, so the distinction is clearly about types.

@yminsky Would you say that the untyped lambda calculus is not pure for some reason?

@jacobmcarthur Nope. Unlike a Haskell program, a lambda calculus term can't send a packet.

@yminsky @jacobmcarthur You can still build up a syntax tree free-monad style without types then send it to an evaluator or do world passing

@kmett @jacobmcarthur By this logic, C is also pure.

@yminsky @kmett Haskell is more comparable to the C preprocessor than C, in this regard.

@jacobmcarthur @kmett Why not all of C? It's just a pure function that generates a description of a computation to be run on a machine...

@yminsky @jacobmcarthur One reason folks tend to use the free monad approach is testability. You can introspect on the terms and validate.