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MiniBASIC Interpreter

First assignment for the course of "Metodologie di Programmazione" held by Roberto Navigli.

Overview

The MiniBASIC class is a simple interpreter designed to execute basic programs written in a language similar to BASIC. It supports a limited set of data types, expressions, and instructions, allowing you to create and run basic scripts.

Features

Data Types

The MiniBASIC language supports three basic data types:

  • Boolean: Represents a true/false value.
  • Positive Integer: Represents non-negative whole numbers.
  • String: Represents sequences of characters.

Expressions

Expressions in MiniBASIC can be:

  • Constants: Direct values like 5, true, or "hello".
  • Variables: The language provides 10 variables ($0 to $9). Variables can hold any type, and their type is determined by the expression assigned to them. For example:
    • $1 = "hello" assigns the STRING type to $1.
    • $5 = 10 assigns the INTEGER type to $5.
  • Operations:
    • Addition: Adding two expressions of the same type results in an expression of that type.
      • "hello" + "!" results in a STRING "hello!".
      • 0 + 42 results in an INTEGER 42.
      • true + false results in a BOOLEAN value representing the logical OR of the two values.
    • Comparison: Comparing two expressions results in a BOOLEAN expression.
      • expression1 == expression2 checks for equality.
      • expression1 <> expression2 checks for inequality.
      • For integers, the operators >, <, <=, and >= are also supported.

Instructions

Each instruction in MiniBASIC must be written on a single line. The supported instructions are:

  • Print: Outputs a variable or a string constant.
    • Example: PRINT $3 or PRINT "hello".
  • Assignment: Assigns an expression to a variable.
    • Example: $3 = 5 + 2.
  • Conditional Execution: Executes instructions based on a boolean expression.
    • Example: IF <boolean expression> THEN instruction1 : instruction2 : ... [ELSE instruction1 : ...].
  • Iteration: Repeats instructions while a boolean expression is true.
    • Example: WHILE <boolean expression> DO instruction1 : ... : instructionN.
  • Labeling: Marks a position in the program with a label, which can be used for jumps.
    • Example: start:.
  • Jump (GOTO): Jumps to a labeled position in the program.
    • Example: GOTO start.
  • Comments: A line beginning with REM is treated as a comment and is ignored by the interpreter.
    • Example: REM This is a comment.
  • End: Ends the execution of the program.
    • Execution also ends when all instructions have been processed.

Usage

Running Programs with MiniBASIC

To use the MiniBASIC interpreter, create an instance of the MiniBASIC class and pass a script written in the MiniBASIC language to it for execution.

Example:

$0 = 5
$1 = 10
IF $0 < $1 THEN PRINT "Five is less than ten" ELSE PRINT "This won't be printed"
PRINT "Done"
END

2 main classes are used: Programma and MiniBASIC which can be found in it/uniroma1/metodologie

  • Loading Programs: The Programma.fromFile(file) method is used to load BASIC scripts from the specified file paths.
  • Executing Programs: The MiniBASIC().esegui(program) method is called to execute each instruction in program.
  • Handling Exceptions: Any exceptions that occur during execution (such as OperatoreNonTrovatoException or TipiIncopamtibiliException) are caught and printed.

Testing with the Test Class

The Test class is provided to demonstrate how the MiniBASIC interpreter can be used to execute various scripts. The class loads several example programs and executes them using the MiniBASIC interpreter.

example can be found in it/uniroma1/metodologie/Test.java and it/uniroma1/metodologie/MiniBASICTest.java