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Allegro CL
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  3.1 Evaluation   3.1.2 The Evaluation Model   3.1.2.1 Form Evaluation   3.1.2.1.1 Symbols as Forms

3.1.2.1.1.4 Symbols Naming Both Lexical and Dynamic Variables

The same symbol can name both a lexical variable and a dynamic variable, but never in the same lexical environment.

In the following example, the symbol x is used, at different times, as the name of a lexical variable and as the name of a dynamic variable.

 (let ((x 1))            ;Binds a special variable X
   (declare (special x))
   (let ((x 2))          ;Binds a lexical variable X
     (+ x                ;Reads a lexical variable X
        (locally (declare (special x))
                 x))))   ;Reads a special variable X
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