Lispkit Lisp

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.

The base language provides the following functions only but extensions are discussed in Henderson's book for the explicit support of lazy evaluation and nondeterministic programming.

atom – given an expression returns True if its value is atomic; False if not

add – given two expressions returns the sum of their numeric values

car – given an expression whose value is a pair, returns the pair's first value

cdr – given an expression whose value is a pair, returns the pair's second value

cons – given two expressions returns a value pair consisting of their values

div – given two expressions returns the quotient of their numeric values

eq – given two expressions returns True if their values are equal; False if not

if – given three expressions returns the value of the second if the value of the first is True, otherwise returns the value of the third

lambda – given an argument list and an expression, returns them as a function

let – given an expression with declarations (as named expressions visible in the expression) returns its value

letrec – like let, except the declared names are also visible in the declarations themselves

leq – given two expressions, returns True if the value of the first is numerically less than or equal to the value of the second; False if not

mod (or rem) – given two expressions, returns the modulus (also known as the remainder) of their numeric values

mul – given two expressions, returns the product of their numeric values

quote – given an expression, returns that expression as a value

sub – given two expressions, returns the difference of their numeric values

The functions, lambda, let, and letrec, are similar but have subtle differences in the way that they treat named variables which make them useful in different ways: lambda defines and returns a function, let binds expressions to variable names, and letrec is essentially similar to let except it allows defining of recursive functions and values, e.g., infinite series.

• Henderson, Peter; Jones, Geraint A.; Jones, Simon B. (1 December 1983). The LispKit Manual. University of Oxford Computing Laboratory. ISBN 978-0902928183.
• Henderson, Peter; Jones, Geraint A.; Jones, Simon B. (1 December 1983). The LispKit Manual: Volume 1 (PDF). Oxford, England: University of Oxford: Computing Laboratory: Programming Research Group.
• Henderson, Peter; Jones, Geraint A.; Jones, Simon B. (1 December 1983). The LispKit Manual: Volume 2 (PDF). Oxford, England: University of Oxford: Computing Laboratory: Programming Research Group.

• Archive of old LispKit Lisp code and files, plus C implementation of SECD machine
• Paper about a LispKit Lisp implementation in Java, and the implementation