YispSharp

YispSharp is a C# implementation of a Lisp interpreter, created using Crafting Interpreters by Robert Nystrom as a guide. This project was developed primarily as an assignment for CS 403/503 - Programming Languages (Fall 2023) at the University of Alabama. The interpreter works on a dialect of Lisp established by our professor, Don Yessick, called Yessick's Lisp or Yisp for short.

The instructions provided for this project can be found here, and some notes on the grammar used to build this interpreter can be found here.

Table of Contents

1. Usage
2. Building
3. Testing
   1. Tests Outline
4. Implementation Details

Usage

When run without an argument, Y# operates as a REPL prompt which runs until it encounters an exit code. Otherwise, when given a Yisp source file, Y# will attempt to execute it and then exit.

YispSharp [Yisp script]

Building

Building and running YispSharp requires the .NET 6.0 SDK. It can be installed via a package manager, such as apt or snap, or from the .NET download website.

sudo apt-get install dotnet-sdk-6.0

On Windows, it can be installed via the Windows Package Manager, winget, or from the aforementioned download site.

winget install Microsoft.DotNet.SDK.6

Once installed, clone the repository to a location of your choosing.

git clone https://github.com/resistiv/YispSharp.git

Navigate to the folder containing the file YispSharp.sln, and run the following:

dotnet build

The resulting executables will be built to the bin subfolders of each project within the solution, from which they can be run.

Testing

This project adapts several of Robert Nystrom's Lox unit tests to Yisp.

Tests can be built and run using the following command in the root of the repository:

dotnet test

The number of successful and failed tests will be displayed. Of important note, some tests will be noted as being skipped; these test sets were used early in development for things like Scanner and Parser testing, and are no longer applicable in the program's current state, thus they are NOT failed tests.

As of commit 4718a06, everything builds, runs, and all tests pass on Windows 10.

Tests Outline

For each built-in function or operation, there is an individual test with cases testing a range of correct and incorrect usages. All of these tests are fairly simple and are made to test the basic functionality of these operations.

Three more complex tests are used to ensure everything is in proper working order. Due to the size of the code for these tests, separate source files are located under the YispTester/TestFiles directory with proper comments and documentation.

• Blackjack: Taken from the Blackjack assignment earlier in the semester, this tests comparisons, list manipulation, and recursion.
• Bowling: Taken from the Bowling assignment earlier in the semester, this tests comparisons, function definitions & lazy evaluation, list manipulation, and recursion.
• Fibonacci: A Fibonacci number calculator which tests comparisons and recursion.

Implementation Details

Some changes were made to the base language for this implementation of Yisp in order to allow for more flexibility. If a change is not mentioned here, it can be assumed that the feature complies with the original project specification. Additionally, lexical closures are not yet implemented due to time concerns.

• Lists (list ...): Lists need to be instantiated using the list function (except for nil, which can be used via () or (list)). This was done to reduce ambiguity when interpreting function calls.
• Addition (+ val1 val2 ...): An addition operation accepts two or more values and adds all of them together.
• Subtraction (- val1 ...): A subtraction operation can perform two tasks:
  • If given only one operand, the value is negated.
  • If given two or more operands, all of the other operands are subtracted from the first operand.
• Multiplication (* val1 val2 ...): A multiplication operation accepts two or more values and multiplies all of them together.
• Quote (quote val) or 'val: In order to allow the symbol? function to work properly, quote was implemented. This had side effects for other functions such as car and cdr, including the need for self-evaluation of numbers, strings, and nil; that is, a quoted version of any of the aforementioned types will be equal to a non-quoted version.
• Eval (eval val): To allow quoted values to be evaluated, eval was implemented.