### 5.4 Deleting a macro ¶

A macro definition can be removed with `undefine`:

Builtin: undefine(name…) ¶

  For each argument, remove the macro name. The macro names must necessarily be quoted, since they will be expanded otherwise.

  The expansion of `undefine` is void. The macro `undefine` is recognized only with parameters.

    foo bar blah
    ⇒foo bar blah
    define(`foo', `some')define(`bar', `other')define(`blah', `text')
    ⇒
    foo bar blah
    ⇒some other text
    undefine(`foo')
    ⇒
    foo bar blah
    ⇒foo other text
    undefine(`bar', `blah')
    ⇒
    foo bar blah
    ⇒foo bar blah

Undefining a macro inside that macro’s expansion is safe; the macro still expands to the definition that was in effect at the ‘`(`’.

    define(`f', ``$0':$1')
    ⇒
    f(f(f(undefine(`f')`hello world')))
    ⇒f:f:f:hello world
    f(`bye')
    ⇒f(bye)

It is not an error for name to have no macro definition. In that case, `undefine` does nothing.