= is invoked as a special form,
place must be a symbol.
= assigns a new value
to the local or global variable currently bound to that symbol. If the symbol has neither
a global nor a local binding, it's an error.
= is also bound to a macro which performs generalized assignment. When
= is invoked
as a macro, if
place is a function call, its callee must be a symbol which is bound
to a registered setter. The macro expands to a call to the corresponding
(= (global 'a) 100) ; ...expands to... (global= 'a 100)
= macro may be invoked with any number of arguments.
(= a b, c d) is equivalent
(= a b) followed by
(= c d).