Suppose you are implementing a relational employee database, where the database

Question

Suppose you are implementing a relational employee database, where the database is a list of tuples formed by the names, the phone numbers and the salaries of the employees. For example, a sample database may consist of the following list of tuples:

Note that I have written parentheses around the tuples to make them more readable, but the precedences of different operators in OCaml make this unnecessary.

Define a function

that takes as input a list representing the database and the name of an employee and returns his/her corresponding salary. Think also of some graceful way to deal with the situation where the database does not contain an entry for that particular name, explain it, and implement this in your code.

Define a function

that is like find_salary, except that it returns the phone number instead.

What I have so far:

let rec find_salary li nm =
let rec helper name s =
match li with
| [] -> 0.0
| (n, p, s) :: t -> if (name = n) then s
else
helper t name

Explanation / Answer

Running the program produces this output:

To accomplish the string reversal, the program converts the string to an array of characters (first for loop), reverses the array into a second array (second for loop), and then converts back to a string.

If you convert the palindrome string to a string builder, you can use the reverse() method in the StringBuilder class. It makes the code simpler and easier to read:

Running this program produces the same output:

Note that println() prints a string builder, as in:

because sb.toString() is call

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