2.1 src/main/scala/project3/Util.scala🔗

This file defines multiple classes that are used to generate the code and run it on your machine. Nothing needs to be modified, but it is recommended to read it and have an idea of what is happening behind the scene.

2.2 gen/bootstrap.c🔗

As we are generating x86-64 assembly code which is OS independent, we will be using GCC/Clang to do the heavy lifting for us. The bootstrap file is a generic C file that is calling a function entry_point and is printing the result to stdout. Our compiler will generate the file gen/gen.s and will be assembled and linked with bootstrap.c by gcc:

gcc bootstrap.c gen.s -o out

2.3 src/main/scala/project3/Main.scala🔗

The main function is defined in this file. The data flow in this file can be viewed as:

Read from file / Read from command line -> Parser -> Semantic analyzer -> Interpreter or compiler

You will be implementing many different parsers in order to test them through the main function.

The AST generated will be then provided to the semantic analyzer. If there is no error, then the code (represented as AST) is going to be interpreted or compiled. The skeleton provides you with one interpreter (ValueInterpreter), but this time there is no reference compiler. You will have to build the StackInterpreter and the X86Compiler.

As our language becomes more complex, it will become more useful to read the input code from a source file. You may find some example programs in the sample/ folder. You could also use the sample programs to test your implementation. Here some examples to run the code either from a file or from the command line:

$ sbt
sbt:Project3> run
Usage: run PROG [OPTION]
   or: run FILE [OPTION]
OPTION: intStack

sbt:Project3> run sample/valid_arithm.scala

sbt:Project3> run sample/valid_arithm.scala intStack

It is still possible to run code from the command line, as in project 1. For example:

$ sbt
sbt:Project3> run "val x = 5; x"
sbt:Project3> run "val x = 5; x" intStack

2.4 src/main/scala/project3/Language.scala🔗

This class contains the definition of our intermediate language.

2.5 src/main/scala/project3/Parser.scala🔗

As we discussed in class, we are introducing types in the language. In addition to Int, we will also have the types Boolean and Unit. You will need to modify the Scanner class in order to tokenize the constants of type Boolean correctly. There is a single Unit constant: (). Because this construct can be used for other reasons (e.g. a function without parameters), the () will still be parsed into two delimiters: ’(’ and ’)’. The function parseAtom will be handling the Unit literal.

The rest of the file is the definition of each parser we are building, starting from the base parser that is an implementation of the parser we implemented in project 2. What you have to do for this project is highlighted with TODOs in the code. We encourage you to read the comments and code carefully before proceeding.

2.6 src/main/scala/project3/SemanticAnalyzer.scala🔗

While the parser is in charge of verifying that the input string follows the defined syntax, the semantic analyzer verifies that the program described is meaningful and follows the typing rules. The skeleton code already contains the semantic checks we implemented in project 2.

However as we have seen in class, we are upgrading our semantic analyzer into a type checker. Your job is to complete the typeInfer function using the rules we have seen in class.

2.7 src/main/scala/project3/Interpreter.scala🔗

As we have seen in class, now that our programming language accepts more than just mathematical expressions, we need to define the required behavior of our language. An interpreter is used to define this meaning.

We provide you with an interpreter (ValueInterpreter) that is fully functional. You should use it as a reference, and your job is to complete the Stack-based interpreter.

2.8 src/main/scala/project3/Compiler.scala🔗

The x86-64 compiler handling all features up to loops is already implemented for you. You need to complete the compiler with the new features.

2.9 src/test/scala/project3/*Test.scala🔗

These files contain some unit tests for the first parsers. In order to get full credits, you must write your own tests for the others. Every task should have at least 2 tests otherwise points will be deducted. There are some functions given to you in order to make the implementation easier; read them carefully and try to use them.

3.1 I/O Primitives🔗

With functions now in our language, we can add a little bit of I/O. When writing code in our programming language, the programmer will have access to two primitives supported by the underlying C-based runtime.

• getchar of type () => Int. See C API doc.

• putchar of type Int => Unit. See C API doc ; we do not return the character.

putchar(72); putchar(101); putchar(108); putchar(108); putchar(111); ...

However, using these functions may lead to some issues when the code is launched from sbt. In order to test, launch the out binary file generated in the folder gen.

3.2 Functions as Values🔗

In the Compiler.scala file, there are some places marked as Extra Credit. These are the places where we need to generate code for functions used as arguments, stored into variables, or returned from a function. While you are required to parse this kind of code correctly and be able to type check it, you are not required to generate the corresponding x86 code. Implementing such generation correctly will be counted as extra credit.

Note: it requires some extra care if you would like to treat these primitive functions (getchar and putchar) as values on Mac/Arm. If you have worked out ordinary functions as values but encounter issues for these primitive functions, post a private post on Piazza and we are happy to offer hints.

4.1 Grading🔗

Your project will be tested against a set of unit tests. The weights of each task will be distributed as follow:

The Function as Value extension is worth 15% extra credit of this project.