## Function: COMMON-LISP:CONSTANTP
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> True of any FORM that has a constant value: self-evaluating objects,
> keywords, defined constants, quote forms. Additionally the
> constant-foldability of some function calls special forms is recognized. If
> ENVIRONMENT is provided the FORM is first macroexpanded in it.

### Lambda list
```cl
(sb-kernel:form &optional sb-c::environment)
```