Lispkit Lisp is a lexically scoped, purely functional subset of Lisp (Pure Lisp) developed as a testbed for functional programming concepts. It was first used for early experimentation with lazy evaluation. An implementation based on a stack, environment, control, dump virtual machine and abstract machine (SECD machine) written in an ALGOL variant was published by the developer Peter Henderson in 1980. The compiler and virtual machine are highly portable and as a result have been implemented on many machines.