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with-open-stream  (var stream)
		   {declaration}* 
		   {form}*
   ⇒  {result}*
var—a variable name.
stream—a form; evaluated to produce a stream.
declaration—a declare expression; not evaluated.
forms—an implicit progn.
results—the values returned by the forms.
with-open-stream performs a series of operations on stream, returns a value, and then closes the stream.
Var is bound to the value of stream, and then forms are executed as an implicit progn. stream is automatically closed on exit from with-open-stream, no matter whether the exit is normal or abnormal.
The stream has dynamic extent; its extent ends when the form is exited.
The consequences are undefined if an attempt is made to assign the the variable var with the forms.
 (with-open-stream (s (make-string-input-stream "1 2 3 4"))
    (+ (read s) (read s) (read s))) ⇒  6
The stream is closed (upon exit).