 Lastly, the Scheme standards documents require tail-call optimization, which the CL standard does not.Most CL implementations do offer tail-call optimization, although often only when the programmer uses an optimization directive.Nonetheless, common CL coding style does not favor the ubiquitous use of recursion that Scheme style prefers—what a Scheme programmer would express with tail recursion, a CL user would usually express with an iterative expression in codice_75, codice_99, codice_72, or (more recently) with the codice_101 package.