Each time the function fact is entered, a new binding of n to its current value is created. These bindings are held on a stack, so that the new binding does not replace the old value of n, but shadows it. When the function fact exits, the binding of n is removed from the stack, leaving the previous value.

The special function trace is very useful for seeing the arguments and results of recursive calls:

   : (trace fact)
   fact

   : (fact 3)
   Entry (fact 3)
   |Entry (fact 2)
   | Entry (fact 1)
   |  Entry (fact 0)
   |  ==> 1
   | ==> 1
   |==> 2
   ==> 6
   6

   : (untrace)

trace

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