GNU Smalltalk Library Reference: Object-testing functionality

ifNil: nilBlock: Evaluate nilBlock if the receiver is nil, else answer self
ifNil: nilBlock ifNotNil: notNilBlock: Evaluate nilBlock if the receiver is nil, else evaluate notNilBlock, passing the receiver.
ifNotNil: notNilBlock: Evaluate notNilBlock if the receiver is not nil, passing the receiver. Else answer nil.
ifNotNil: notNilBlock ifNil: nilBlock: Evaluate nilBlock if the receiver is nil, else evaluate notNilBlock, passing the receiver.
isArray: Answer ‘false’.
isBehavior: Answer ‘false’.
isCObject: Answer ‘false’.
isCharacter: Answer ‘false’.
isCharacterArray: Answer ‘false’.
isClass: Answer ‘false’.
isFloat: Answer ‘false’.
isInteger: Answer ‘false’.
isKindOf: aClass: Answer whether the receiver’s class is aClass or a subclass of aClass
isMemberOf: aClass: Returns true if the receiver is an instance of the class ’aClass’
isMeta: Same as isMetaclass
isMetaClass: Same as isMetaclass
isMetaclass: Answer ‘false’.
isNamespace: Answer ‘false’.
isNil: Answer whether the receiver is nil
isNumber: Answer ‘false’.
isSmallInteger: Answer ‘false’.
isString: Answer ‘false’.
isSymbol: Answer ‘false’.
notNil: Answer whether the receiver is not nil
respondsTo: aSymbol: Returns true if the receiver understands the given selector