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Scoping Constructs
The flexibility of Mathematica's symbolic architecture is reflected in its rich collection of carefully defined constructs for localization and modularization. The use of multiple forms of scoping allows for more elegant, readable and efficient programs, supports the concept of programs as data, and allows direct correspondence with mathematical notions of variables.
With evaluate with specified variables replaced by values
    
Module localize names of variables (lexical scoping)
Block localize values of variables (dynamic scoping)
    
DynamicModule localize names of variables in dynamic interface constructs
    
Constructs with Automatic Name Scoping
Function a pure function, with formal variables automatically scoped
Rule (->), RuleDelayed (:>) — named pattern variables automatically scoped
Set (=), SetDelayed (:=) — named pattern variables automatically scoped
Constructs with Automatic Value Scoping
Table create a table, with iterator variables automatically scoped
Do  ▪ Sum  ▪ Plot  ▪ Plot3D  ▪ NDSolve  ▪ ...
Other Forms of Scoping
Begin, End localize symbol namespace
Throw, Catch localize exceptions
Quiet, Check localize messages
BlockRandom localize pseudorandom variables
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