Crux

a minimal Lisp variant

One of the simplest practical programming languages is Lisp.  Programs contain
expressions which are atoms or lists.  Atoms are booleans, integers, strings,
variables, functions or macros.  Lists can contain other lists.

Running programs is evaluating expressions.  Evaluating atoms, except for
variables, returns them.  Evaluating variables involves environments.
Evaluating lists involves function or macro invocations.

The following functions are always in the environment.  The first five functions
involve special evaluation procedures.

        ne
        if
        set
        func
        macro
        equal
        atom
        first
        rest
        append
        add
        negate
        gt

See the source code and other Lisp resources for further details.