form—a form; evaluated as described below.
results—the values returned by the form.
step implements a debugging paradigm wherein the programmer
is allowed to step through the evaluation of a form.
The specific nature of the interaction,
including which I/O streams are used and
whether the stepping has lexical or dynamic scope,
is implementation-defined.
step evaluates form in the current environment.
A call to step can be compiled, but it is acceptable for an
implementation to interactively step through only those parts of the computation
that are interpreted.
It is technically permissible for a conforming implementation
to take no action at all other than normal execution of the form.
In such a situation,
(step form)
is equivalent to, for example,
(let () form).
In implementations where this is the case, the associated documentation
should mention that fact.
Implementations are encouraged to respond to the typing of ?
or the pressing of a “help key” by providing help including a list of
commands.