CS280-Project-4

Interpreter

Final Project for my course in Programming Language Concepts. We've built upon previous projects (Lexical Analyzer and Parser) and added the final step in producing a usable programming language: the Interpreter.

Written in C++

Variables

Assign variables using a let statement.

• let expects an identifier and an Integer or String expression.
• Valid identifiers are alphanumeric but can contain underscores, and must begin with a letter.

  let age 20;
  let name "Ricky";

Integers

Integer expressions follow PEMDAS order of operations and can include other Integer variables within them.

  let year 2020;
  
  let radius 10;
  let areaOfCircle 3.14 * radius ^ 2;

Strings

• String literals and String expressions are supported.
• String concatenation uses the + operator
• String multiplication (repeated concatenation) uses the * operator.

  let firstName "Ricky";
  let lastName "Palaguachi";
  let fullName firstName + " " + lastName; // "Ricky Palaguachi"
  
  let eightZeros "0" * 8;     // "00000000"
  let alphabet "abcdef" * 2;  // "abcdefabcdef"

Print statements

To print to stdout, use a print statement.

• print expects a String variable or String expression.

  print "Hello, World!\n";  // "Hello, World!"
  print "I am " + name;     // "I am Ricky"
  print "0" * 16;           // "0000000000000000"

Conditional Expressions

Conditional experssions can be used within the header of an if statement or a loop statement.

• A false boolean value is encoded by the Integer value of 0
• A true boolean value is any nonzero Integer.

If Statements

There are if statementes for conditional execution:

  if 0 BEGIN
    //code goes here
  END

Loop Statements

There are "Loop" Statements for iterative execution:

  loop 1 BEGIN
    //code goes here
  END

• The body of the loop is enclosed by the BEGIN and END reserved words
• A true boolean expression is encoded by the Integer value 1

Error handling

Error checking is done in phases when analyzing the source file, and can occur when parsing or executing.

1. Syntax Error When the regular grammer of the language is violated.
2. Runtime error Occurs during runtime. A common example: using an undeclared variable.

Error messages display the line number where the error occured.

To use this language, write code into a file and pass the file's name as a command-line-argument.