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KAIST CS320 Assignment Instructions

The course has 5 coding exercises (no submission required) and 3 projects (submission required).

Prerequisites

Download

Run sbt new kaist-plrg-cs320/[assignment name].g8 in your terminal. The project directory whose name is the same as the assignment will be created under the current directory.

Below is an example.

$ sbt new kaist-plrg-cs320/scala-tutorial.g8
...
name [Scala Tutorial]:
Template applied in ./scala-tutorial

See the instructions for each assignment to find the exact assignment name.

Directory Structure

You can find the following directories and files in the project directory:

core/src
- main/scala
  - cs320
    - Implementation.scala
    - Template.scala
  - package.scala
- test/scala
  - cs320
    - Spec.scala

DO NOT edit files other than core/src/main/scala/cs320/Implementation.scala and core/src/test/scala/cs320/Spec.scala.

  • core/src/main/scala/cs320/Implementation.scala: You must fill this file to implement the required function(s). It is enough to edit only this file to finish the assignment.

  • core/src/main/scala/cs320/Template.scala: This file contains the definitions of functions that you must implement to complete the assignment.

  • core/src/main/scala/package.scala: This file defines error functions. You can throw an exception with an error message s by calling error(s). To omit the message, you can use error(), instead of error("").

  • core/src/test/scala/cs320/Spec.scala This file contains test cases. Passing all the provided tests does not guarantee that your implementation is correct. We highly recommend adding your own tests.

Restrictions

You must not use any of the following features in your implementation:

  • asInstanceOf
  • isInstanceOf
  • null
  • return
  • throw
  • var
  • while
  • try-catch
  • mutable data structures

You can use any other features that are not explicitly forbidden. For example,

  • You can define helper functions and additional types.
  • You can use immutable data structures.
  • You can use for.
  • You can mutate mutable variables/fields already defined in the provided code.

The use of the prohibited features will make your code not compile. If your code compiles successfully, you are not using any prohibited features.

Testing Your Implementation

Under the project directory, execute sbt to start an sbt console.

$ sbt
[info] welcome to sbt
...
sbt:...>

To run the test cases in Spec.scala, execute the test command. Every test case will fail at the beginning.

sbt:...> test
...
[error] Failed tests:
[error]         cs320.Spec

After implementing every function correctly, every test will succeed.

sbt:...> test
...
[info] All tests passed.

(If you are working on Exercise #1, stop reading here. The remaining parts are for the other assignments.)

REPL

Any assignments other than Exercise #1 provide REPL. REPL allows you to input an arbitrary expression into your implementation and see the result. Using REPL, you can quickly test your implementation without changing Spec.scala.

Execute the run command to start REPL. Below is REPL of Exercise #3.

sbt:mvae > run
[info] running cs320.Main
Welcome to the MVAE REPL.
Type in :q, :quit, or the EOF character to terminate the REPL.

MVAE>

REPL will not work properly at the beginning.

MVAE> { val x = (1, 2); (x + x) }
  Parsed: Val(x,Num(List(1, 2)),Add(Id(x),Id(x)))
scala.NotImplementedError: an implementation is missing
        at scala.Predef$.$qmark$qmark$qmark(Predef.scala:347)
        at cs320.Implementation$.interp(Implementation.scala:18)

After finishing the implementation, REPL will behave correctly.

MVAE> { val x = (1, 2); (x + x) }
  Parsed: Val(x,Num(List(1, 2)),Add(Id(x),Id(x)))
  Result: (2, 3, 3, 4)

(If you are working on an exercise, stop reading here. The remaining parts are for the projects.)

Fuzzing

Each project (but no exercise) provides a fuzzer. A fuzzer randomly generates expressions to test your interpreter. You need to install Node.js on your machine to use the fuzzer.

Execute the run fuzzer command to use the fuzzer.

sbt:... > run fuzzer
[info] running cs320.Main fuzzer
10000

The number shown on the screen is the number of expressions your interpreter correctly interpreted so far. The fuzzer runs forever until it finds a wrong behavior. Press ctrl+c to stop fuzzing.

When the fuzzer finds a wrong behavior, it prints detailed information and terminates.

Incorrect behavior detected
Expr: (1 + 2)
Correct result: 3
Your result: Unexpected Error
an implementation is missing
        scala.Predef$.$qmark$qmark$qmark(Predef.scala:344)
        cs320.Implementation$.interp(Implementation.scala:7)
        cs320.Template.run(Template.scala:5)
        cs320.Template.run$(Template.scala:5)
        cs320.Implementation$.run(Implementation.scala:5)

If the fuzzer reports a failed case after you press ctrl+c, it is due to the abrupt termination, not a defect in your implementation, so you can ignore it.

If your implementation correctly interprets a huge number of expressions, your implementation is highly likely to be correct.

Grading

You must submit your Implementation.scala of each project. See the instructions for each project to find the submission link.

Violation of the honor code will give you F. You must work on each project by yourself without getting any help. You can refer to the lecture materials, including the lecture slides, the textbook, and the sample solutions to the exercises.

We disallow late submissions. If you submit multiple times, only the last submission will be graded.

You can get maximum 100 points. If your code uses a disallow feature or does not compile, you will get 0 points.

  • Test cases: 80 points (1 point per case)
  • Fuzzing: 20 points

The test cases for the grading are similar to, but not the same as, those provided in Spec.scala. You get more points as you pass more test cases. The execution of each test case does not affect the others, e.g., the other test cases will be graded properly even when your implementation runs forever for a certain test case.

If your implementation passes all the test cases, we test the implementation with the same fuzzer as the one you have. We use 10,000 expressions for each student. The expressions are the same for every student. If your implementation behaves correctly for every expression, you will get 20 points for the Fuzzing part. Otherwise, you will get 0 points.

FAQ

My code does not terminate or emits stack overflow error

Though not the only cause, this usually happens in student's implementation when student tries to call error() function with some string interpolation, for example

error(s"not both number: $x, $y")

Maybe changing the code to use plain string might solve the issue, like

error(s"not both number")