Simple Lexical Parser as an assignment I was thrown at for an interview
Write a calculator program in your programming language of choice that evaluates expressions in a very simple integer expression language. The program takes an input on the command line, computes the result, and prints it to the console. For example:
% java calculator.Main “mult(2, 2)”
4
Here are a few more examples:
| Input | Output |
|---|---|
| add(1, 2) | 3 |
| add(1, mult(2, 3)) | 7 |
| mult(add(2, 2), div(9, 3)) | 12 |
| let(a, 5, add(a, a)) | 10 |
| let(foo, 5, let(bar, mult(foo, 10), add(bar, foo))) | 55 |
| let(a, let(b, 10, add(b, b)), let(b, 20, add(a, b))) | 40 |
An expression consists of:
- Numbers: Integers between Integer.MIN_VALUE and Integer.MAX_VALUE
- Variables: Strings of characters, where each character is one of a-z, A-Z
- Arithmetic functions: Add, sub, mult, div, each taking two arbitrary expressions as arguments. In other words, each argument may be any of the expressions on this list.
- A “let” operator for assigning values to variables: let(, , )
As with arithmetic functions, the expression where the variable is used may be an arbitrary expression from this list.