AST Interpreter for RPAL Language

An interpreter to execute an Abstract Syntax Tree of an RPAL program.

RPAL or Right-reference Pedagogic Algorithmic Language is a simple functional programming language. The interpreter takes an Abstract Syntax Tree (AST) of an RPAL program and executes it. The interpreter is implemented following the operational semantics of the RPAL language and the CSE rules. Following is an AST for a sample program to find whether a given number is positive, negative, or zero.

let
.function_form
..<ID:positive_negative>
..<ID:x>
..->
...ls
....<ID:x>
....<INT:0>
...<STR:'Negative'>
...->
....eq
.....<ID:x>
.....<INT:0>
....<STR:'Zero'>
....<STR:'Positive'>
.gamma
..<ID:Print>
..tau
...gamma
....<ID:positive_negative>
....neg
.....<INT:10>
...gamma
....<ID:positive_negative>
....<INT:0>
...gamma
....<ID:positive_negative>
....<INT:10>

Compiling and Running

The project can be compiled by running the following command in the /src directory.

make

It will produce an executable named myrpal. To run the interpreter, run the myrpal executable with the filename as a command line argument to specify the file containing the AST of the RPAL program.

myrpal filename

The output of the program will be printed to the standard output.

Compile with Microsoft C++ toolset on Windows

Install instructions for the toolset are available here. To compile the project, open a Visual Studio developer command prompt (or powershell) and run the following command in the /src directory.

nmake -f Makefile.win

It will produce an executable named myrpal.exe. To run the interpreter, run the myrpal.exe executable with the filename as a command line argument to specify the file containing the AST of the RPAL program.

myrpal.exe filename

The output of the program will be printed to the standard output.

Additional Command Line Arguments

Following commandline arguments are allowed before the filename:

• -ast: Prints the AST of the RPAL program to the standard output.
• -st: Prints the ST of the RPAL program to the standard output.
• -cs: Prints the Control Structures of the RPAL program to the standard output.
• -exe: Prints the Execution of the RPAL program to a file named exec.txt.

Testing

Sample RPAL programs are provided in the /src/tests directory. The CppTest library is used to run tests. It can be installed on Ubuntu using the following command:

sudo apt-get install libcppunit-dev

To run the tests, compile the interpreter and then run the following command in the /src directory.

make test

The test results will be printed to the standard output.