WolframLang: Symbol

What is a Symbol

A symbol in WolframLang is similar to identifiers (e.g. variable names and function names) in Python/Java/JavaScript and other programing languages. Or, it is like lisp's symbol. [see Emacs Lisp: Symbol]

But WolframLang symbol can be held unevaluated, just as a inert name by itself. It need not have a value.

Any sequence of letters you type into wolfram lang become symbols.

For example:

xlist = {3, 4, b+1}
(* {3, 4, 1 + b} *)

(* b is a symbol. no value. stand for itself. *)

(* set a value for b *)
b = 99
(* 99 *)

xlist
(* {3, 4, 100} *)
(* b now has value. *)

another example:

xlist = Table[ {a, b}, {a, 1, 3} ]
(* {{1, b}, {2, b}, {3, b}} *)
(* b is a symbol. no value. stand for itself. *)

(* set a value for b *)
b = 99

xlist
(* 
{{1, 99}, {2, 99}, {3, 99}}
b now has value.
*)

WolframLang code is essentially a sequence of symbols and operators, such as , [] () + - * / # & etc. [see WolframLang Syntax/Operators]

Some of the symbols, builtin or user-defined, has value. When a symbol has a value, the value automatically replaces the symbol. (or the function's return value replaces it.) This constitutes the heart of WolframLang computational model, a term-rewriting system.

Context of a Symbol (Namespace)

Each symbol, are in particular “context” path. This is similar to a file name has a full path including the dir name. WolframLang “context” is similar to the directory path, or like “namespace” in many programing languages.

The GRAVE ACCENT mark ` is used for context separator, similar to the slash for file path.

• Builtin symbol typically has context "System`"
• User-defined symbol typically has context "Global`"

Context[symbol]

return the context (a string) of a symbol.

Context

Context[Sin]
(* "System`" *)

Create Symbol Programatically (Convert String to Symbol, Symbol to String)

Symbol["name"]

Create a symbol, if not already exist. Symbol

SymbolName[symbol]

return the symbol name. SymbolName

List Existing Symbols

Names[pattern]

list existing symbols by a String pattern (regex) .
Names

(* list all symbols whose name contains String *)
Names["*String*"]

Remove a symbol

Remove

Clear a Symbol's Value

• Clear
• ClearAll

Check If a Symbol Has Value

ValueQ