Scan
 Usage
• Scan[f, expr] evaluates f applied to each element of expr in turn.
• Scan[f, expr, levelspec] applies f to parts of expr specified by levelspec.
Notes
• Scan[f, expr] discards the results of applying f to the subexpressions in expr. Unlike Map, Scan does not build up a new expression to return. • You can use Return to exit from Scan. Return[ret] causes the final value of Scan to be ret. If no explicit return values are specified, the final result from Scan is Null. • You can also use Throw to exit from Scan. • Scan is useful in carrying out an operation on parts of expressions where the operation has a "side effect", such as making an assignment. • Level specifications are described in Section A.3.6. • The default value for levelspec in Scan is {1}. • If expr is a SparseArray object, Scan[f, expr] applies f only to the values or subarrays that explicitly appear in expr. • New in Version 1; modified in 3.
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