Symbol in LISP

1. Symbols Definition

SymbolsAre used for theirObjectIdentity to name varous entities
InCommon LISP, Including (but not limited to) Linguistic entities such
AsVariablesAndFunctions.

 

2. built-in symbol

Intern symbol --Interned SymbolIs uniquely identifiable by its
NameFrom anyPackageIn which it isAccessible.

 

3. Convert the string to symbol

;;;

; Description: the right side of the code => "..." indicates the output of each line of code.

;;;

(SETF symbol-string "sym") => "sym"

(SETF symbol-object (intern symbol-string) => sym

(Symbolp symbol-object) => T

(SETF (get symbol-object 'symbol-name) "sym") => "sym"

(SETF (get symbol-object 'symbol-value) "sym") => "sym"

 

4. symbol Structure

Each symbol has the following main structure:

; Name ---> "foo"

; Package ---> in some package

; Value ---> 27

; Function --- ># <function>

; Plist ---> (color red)

From Paul Graham's ANSI Common Lisp. p135

 

5. fboudp checks whether a symbol is a function name.

(Fboundp 'acs-Main-loop) => T; ACs-Main-loop is a function name.

(Fboundp 'asymbol) => nil; asymbol is just a symbol

 

6. Determine whether a symbol is a class name

(Find-class 'patc-pattern nil) => T; patc-pattern is a class name

(Find-class 'patx-pattern nil) => nil; patx-pattern is not a class

Pay attention to the following parameters of find-class:

Syntax:

Find-class Symbol& OptionalErrorp Environment=> Class

(SETF(Find-class Symbol& OptionalErrorp
Environment)New-class)

When errorp is set to nil, type error is not thrown.