CMU 15-112 Summer 2018: Fundamentals of Programming and Computer Science
Homework 5 Bonus (Due Wed 11-Jul, at 10pm)

• This assignment is SOLO. This means you may not look at other student's code or let other students look at your code for these problems. See the syllabus for details.


• To start:
  1. Download hw5-bonus.py to your 'week2' folder
  2. Edit hw5-bonus.py using Pyzo
  3. When you are ready, submit hw5-bonus.py to Autolab. For this hw, you may submit up to 10 times, which is fewer times than you've had in the past but only your last submission counts.
  4. You will have fewer test cases given to you this time around.
• Do not use sets, dictionaries, or recursion in this assignment.
• Do not hardcode the test cases in your solutions.

Bonus

Note: The course staff is not required to help you with this problem since it is bonus, and it is intended to be challenging.


1. Bonus/Optional: runSimpleProgram(program, args) [4 pts]
   First, carefully watch this video that describes this problem.
   Then, write the function runSimpleProgram(program, args) that works as described in the video, taking a legal program (do not worry about syntax or runtime errors, as we will not test for those cases) and runs it with the given args, and returns the result.
   
   Here are the legal expressions in this language:
   
   
   • [Non-negative Integer]
     Any non-negative integer, such as 0 or 123, is a legal expression.
   
   
   • A[N]
     The letter A followed by a non-negative integer, such as A0 or A123, is a legal expression, and refers to the given argument. A0 is the value at index 0 of the supplied args list. It is an error to set arg values, and it is an error to get arg values that are not supplied. And you may ignore these errors, as we will not test for them!
   
   
   • L[N]
     The letter L followed by a non-negative integer, such as L0 or L123, is a legal expression, and refers to the given local variable. It is ok to get an unassigned local variable, in which case its value should be 0.
   
   
   • [operator] [operand1] [operand2]
     This language allows so-called prefix expressions, where the operator precedes the operands. The operator can be either + or -, and the operands must each be one of the legal expression types listed above (non-negative integer, A[N] or L[N]).
   
   And here are the legal statements in this language (noting that statements occur one per line, and leading and trailing whitespace is ignored):
   
   
   • ! comment
     Lines that start with an exclamation (!), after the ignored whitespace, are comments and are ignored.
   
   
   • L[N] [expr]
     Lines that start with L[N] are assignment statements, and are followed by the expression (as described above) to be stored into the given local variable. For example: L5 - L2 42 This line assigns (L2 - 42) into L5.
   
   
   • [label]:
     Lines that contain only a lowercase word followed by a colon are labels, which are ignored except for when they are targets of jump statements.
   
   
   • JMP [label]
     This is a jump statement, and control is transferred to the line number where the given label is located. It is an error for such a label to not exist, and you may ignore that error.
   
   
   • JMP+ [expr] [label]
     This is a conditional jump, and control is transferred to the line number where the given label is located only if the given expression is positive. Otherwise, the statement is ignored.
   
   
   • JMP0 [expr] [label]
     This is another kind of conditional jump, and control is transferred only if the given expression is 0.
   
   
   • RTN [expr]
     This is a return statement, and the given expression is returned.
   
   Hints:
   1. Do not try to translate the program into Python! Even if you could do so, it is not allowed here. Instead, you are going to write a so-called interpreter. Just keep track of the local variables, and move line-by-line through the program, simulating the execution of the line as appropriate.
   2. You will find it useful to keep track of the current line number.
   3. How long do you run the program? Until you hit a RTN statement! You may assume that will always eventually happen.
   4. We used strip, split, and splitlines in our sample solution, though you of course may solve this how you wish.
   
   Finally, here is a sample test function for you. You surely will want to add some addition test cases. In fact, a hint would be to build your function incrementally, starting with the simplest test cases you can think up, which use the fewest expression and statement syntax rules. Then add more test cases as you implement more of the language.
   def testRunSimpleProgram(): print("Testing runSimpleProgram()...", end="") largest = """! largest: Returns max(A0, A1) L0 - A0 A1 JMP+ L0 a0 RTN A1 a0: RTN A0""" assert(runSimpleProgram(largest, [5, 6]) == 6) assert(runSimpleProgram(largest, [6, 5]) == 6) sumToN = """! SumToN: Returns 1 + ... + A0 ! L0 is a counter, L1 is the result L0 0 L1 0 loop: L2 - L0 A0 JMP0 L2 done L0 + L0 1 L1 + L1 L0 JMP loop done: RTN L1""" assert(runSimpleProgram(sumToN, [5]) == 1+2+3+4+5) assert(runSimpleProgram(sumToN, [10]) == 10*11//2) print("Passed!")