The standard let form binds variables whose names are known
at compile-time. The cl-progv form provides an easy way to
bind variables whose names are computed at run-time.
This form establishes let-style variable bindings on a
set of variables computed at run-time. The expressions
symbols and values are evaluated, and must return lists
of symbols and values, respectively. The symbols are bound to the
corresponding values for the duration of the body forms.
If values is shorter than symbols, the last few symbols
are bound to nil.
If symbols is shorter than values, the excess values
are ignored.