CS664 - Assignment 3

For this assignment, we will create an interpreter for the PicoScript language. It works by reading tokens one at a time, and either pushing them onto the operand stack or invoking some operator. The language specification has been updated in the ‘Library’ section to describe approximately 30 built-in operators.

Start by watching these two videos, which demonstrate the way the lexer and interpreter work together.

Assignment 2 solution [51:10]
Assignment 3 overview [1:15:24]

As you can see, I provided the basic structure of the interpreter. You should get the rest of it working:

Implement the operators in the library specification. They will all be methods in the Interpreter class, similar to the ones I did for you: add, mul, def, and dup. However, some of them may require additional facilities in the Value class and elsewhere.
For example, the section on relational operators describes Boolean values, which I did not support yet. You will need to add a new Value type BOOL and a matching field and constructor. Then update the toString method to print Booleans.
Each operator defined in the library specification comes with a series of examples of its usage. Those examples are also unit tests in the classes that end with Operators, such as ArithmeticOperators and StackOperators.
Finally, try defining one or more of these procedures in PicoScript (not in Java):
- pow should calculate integer powers. For example:
```
2 8 pow    % [256]
```
```
5 6 pow    % [15625]
```
```
7 15 pow    % [4747561509943]
```
- fact should calculate the factorial function – the product of all integers between 1 and $N$.
```
5 fact    % [120]
```
```
10 fact    % [3628800]
```
```
42 fact    % [1405006117752879898543142606244511569936384000000000]
```
- fibs should generate a list of the first $N$ Fibonacci numbers on the stack. For example:
```
5 fibs    % [1,1,2,3,5]
```
```
10 fibs   % [1,1,2,3,5,8,13,21,34,55]
```
```
30 fibs   % [1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,
          %  2584,4181,6765,10946,17711,28657,46368,75025,121393,
          %  196418,317811,514229,832040]
```
- fillstr should take the ASCII/Unicode value of a character, and generate a string in which it is repeated $N$ times. For example:
```
46 10 fillstr    % [..........]
```
```
36 4 fillstr    % [$$$$]
```
  The 46 is the ASCII value of the dot ‘.’ and 36 is the dollar sign ‘$’.
To submit any of these PicoScript definitions, save them into your assn3 directory using the operator name and the extension .ps – for example, fillstr.ps could contain:
```
/fillstr {  % My procedure definition
  BLAH BLAH % Your code goes here
} def
% And then some test cases
46 10 fillstr
36 4 fillstr
```
Then if you paste the above into the interactive interpreter, it should show the resulting stack as:
```
[.........., $$$$]
```

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