A201/A597 Introduction to Programming I (4/3 cr.)

Spring Semester 2002

Homework Assignment Six: A Very Basic Interpreter (Evaluator)

For this assignment you are to write an arithmetic expression evaluator that is able to perform

additions,
multiplications
subtractions, and
divisions,

is able to

store results in named locations (variables) and
allow them in expressions as well,

as illustrated in the sample session below. The evaluator should also handle parentheses properly.

Here's a sample session with the program:

frilled.cs.indiana.edu%java Eval
Eval> 1 + 1
1 + 1 
2 
Result is: 2 
Eval> ( 1 + 2 ) * 3
( 1 + 2 ) * 3 
( 3 ) * 3 
3 * 3 
9 
Result is: 9 
Eval> a = 1 + 1
1 + 1 
2 
Stored 2 in a
Eval> a 
2 
Result is: 2 
Eval> a = a + 1
2 + 1 
3 
Stored 3 in a
Eval> a
3 
Result is: 3 
Eval> b = a - 4
3 - 4 
-1 
Stored -1 in b
Eval> a
3 
Result is: 3 
Eval> b
-1 
Result is: -1 
Eval> a = ( a - b ) * ( a + b )
( 3 - -1 ) * ( 3 + -1 ) 
( 4 ) * ( 3 + -1 ) 
( 4 ) * ( 2 ) 
4 * ( 2 ) 
4 * 2 
8 
Stored 8 in a
Eval> a
8 
Result is: 8 
Eval> b
-1 
Result is: -1 
Eval> b = a + b * 4
8 + -1 * 4 
8 + -4 
4 
Stored 4 in b
Eval> a / b
8 / 4 
2 
Result is: 2 
Eval> a = a / b
8 / 4 
2 
Stored 2 in a
Eval> a
2 
Result is: 2 
Eval> b
4 
Result is: 4 
Eval> exit
frilled.cs.indiana.edu%

You may safely assume that

your only operands are integers and that
the names of variables are comprised of only alphabetical characters.

Note that in my evaluator the tokens (numbers, parens) are separated by spaces.

Here's a grading scale for this assignment:

Task	Points
Reading the data line by line and storing it properly	2.0
Being able to support `+` and `-`	2.0
Supporting `*` and `/`	2.0
Allowing named variables to store values	1.5
Allowing named variables in expressions	1.5
Providing error-checking through `try-catch` blocks	1.0
Total	10.0

Please let us know if you have any questions.

Last updated: Mar 31, 2002 by Adrian German for A201