WolframLang: Local Variable

• To create local variables, use Module.
• To create local constants, use With.

Module[{var1, var2 etc}, body]

• Eval body with temp local variables.
• Each of the variable var can be the form var = val or you can set the value in the body by var = val;
• Return the value of body.

Module

Tip: This is similar to “lexical scoped” construct in most programing languages, or lisp's let

When the body is more than one expression, add semicolon between them. [see CompoundExpression and Semicolon]

Module[{x = 3}, x+1] == 4

x = 5;

Module[{x},
 x = 3;
 x+1] == 4

x == 5
(* x is still 5 *)

Warning: The latter variable's value expression do not know the previous variable's value. E.g. Module[{x = 2, y = x}, y] === x

Module[{x=2, y=x}, y] === x

To assign variable that depends on previous variable value, put the assignment in body:

Module[{x=2, y},
y=x;
y] == 2