CS280: PLSL Parser & Interpreter

The following is an interpreter I developed for my CS280 (Programming Language Concepts) class.

This project is built on two other components that I had developed earlier in the class.

1. A lexical analyzer
2. A recursive-descent parser for a Pascal-Like Simple Language.

The grammar rules of the PLSL was described in EBNF notations.

Interpreter Functions

Using previous components (lexical analyzer and parser), the interpreter is responsible for:

1. Building information of variables types in a map container for all the defined variables.

2. Evaluating expressions and determining their values and types.

3. Using a map container that keeps a record of the defined variables in the parsed program.

4. Printing the results of an unsuccessful parsing and interpreting by the parser/interpreter functions, as well as error messages that might be detected by the lexical analyzer.

PLSL Description

The PLSL consists of three main parts in the respective order.

1. Program Declaration
2. Variable Declaration
3. Program Body

Program Declaration

The Program Declaration block consists of PROGRAM token followed by an identifier in the beginning of a program. PROGRAM circle;

Variable Declaration

The Variable Declaration block is where the variables that will be used in the program are declared. The block is start with the VAR token then followed by variable declarations.

VAR
	r, a, p, b : REAL;
	i, j, sum : INTEGER;
	str1, str2: STRING; 

Types

PLSL has three different types.

1. INTEGER
2. REAL
3. STRING

Program Body

The beginning of the Program Body is defined by the BEGIN token and the end of the body is defined with the END token.

BEGIN
	i := 8;
	p := 6;
	a := 0;
	sum := 0;
	str1 := 'Hello World!';
	j := -3;
	IF ( p < 5) THEN
		a := (3.14) + j * - p
	ELSE
		IF (p > 0 ) THEN 
			str1 := 'Goodbye!';
	(*Display the results*)
	WRITELN ('The output results are: ' , p, ' ', str1, ' ', a, ' ', i);
END