Retrieve the current definition of a key.
Retrieve the current definition of a key.
NoSuchElementException
when the key is undefined
in this environment.
Tells whether key
is defined in this environment.
Retrieve the current definition of a key, but only if it is defined.
Retrieve the current definition of a key if it is defined.
Retrieve the current definition of a key if it is defined.
If it is not defined, orElse
is evaluated and returned.
Create a derived environment where key
is bound to
value
; previous bindings of key
are shadowed.
Clear the binding for the given key.
Clear the binding for the given key. Lookups for key
will be
negative in the returned environment.