It is possible to rename an already defined macro. To do this, you
need the builtin `defn':
which expands to the *quoted definition* of NAME. If the argument is
not a defined macro, the expansion is void.
If NAME is a user-defined macro, the quoted definition is simply the
quoted expansion text. If, instead, NAME is a builtin, the expansion
is a special token, which points to the builtin's internal definition.
This token is only meaningful as the second argument to `define' (and
`pushdef'), and is ignored in any other context.
Its normal use is best understood through an example, which shows
how to rename `undefine' to `zap':
In this way, `defn' can be used to copy macro definitions, and also
definitions of builtin macros. Even if the original macro is removed,
the other name can still be used to access the definition.
The macro `defn' is recognized only with parameters.
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