Splices a form into its parent form.

splice is meaningless during normal evaluation. It's only meaningful when encountered during macro expansion.

The expander replaces the splice form with all of its argument forms. Note that splice may have any number of arguments, including zero.

For example, a macro expander could introduce both a let form and a defer form into its current lexical scope by returning this splice form:

(splice (let a 10) (defer b))