Let*
Binding of lexically scoped (local) variables
Examples
(let* ((x (* x x))
(y (* 2 x)))
(list x y))
(let* ((x (* x x))
(y (* 2 x))
(x (* x y))
(a (* x x)))
(declare (ignore a))
(list x y))
If the forms above are executed in an environment in which x has the
value -2, then the respective results are '(4 8) and '(32 8).
See let for a discussion of both let and let*, or read on
for a briefer discussion.
The difference between let and let* is that the former binds
its local variables in parallel while the latter binds them sequentially.
Thus, in let*, the term evaluated to produce the local value of one of
the locally bound variables is permitted to reference any locally bound
variable occurring earlier in the binding list and the value so obtained is
the newly computed local value of that variable. See let.
In ACL2 the only declare forms allowed for a let* form are
ignore, ignorable, and type. See declare. Moreover, no
variable declared ignored or ignorable may be bound more than once.
A variable with a type declaration may be bound more than once, in which case
the type declaration is treated by ACL2 as applying to each binding occurrence
of that variable. It seems unclear from the Common Lisp spec whether the
underlying Lisp implementation is expected to apply such a declaration to more
than one binding occurrence, however, so performance in such cases may depend
on the underlying Lisp.
Let* is a Common Lisp macro. See any Common Lisp documentation for
more information.
