# Number of procedure calls

In software-testing applications, it is useful to be able to count the number of times a given procedure is called during the course of a computation. Write a procedure
`make-monitored`

that takes as input a procedure,
`f`

, that itself takes one input. The result returned by
`make-monitored`

is a third procedure, say
`mf`

, that keeps track of the number of times it has been called by maintaining an internal counter. If the input to
`mf`

is the special symbol
`how-many-calls?`

, then mf returns the value of the counter. If the input is the special symbol reset-count, then
`reset-count`

, `mf`

resets the counter to zero. For any other input,
`mf`

returns the result of calling
`f`

on that input and increments the counter. For instance, we could make a monitored version of the
`sqrt`

procedure:

```
(define s (make-monitored sqrt))
(s 100)
10
(s 'how-many-calls?)
1
```