Smaller Basic

A Python interpreter using ANTLR4 as a parser generator for a version of Microsoft's Small Basic language renamed "Smaller Basic."

Examples of source code

Location of this source code: source_code/source.sb.

Sub x_as_int
    If (x = "1") Then x = 1 EndIf
    If (x = "2") Then x = 2 EndIf
    If (x = "3") Then x = 3 EndIf
    If (x = "4") Then x = 4 EndIf
    If (x = "5") Then x = 5 EndIf
    If (x = "6") Then x = 6 EndIf
    If (x = "7") Then x = 7 EndIf
    If (x = "8") Then x = 8 EndIf
    If (x = "9") Then x = 9 EndIf
EndSub

Sub main
    While (true)
        IO.WriteLine("Enter a number from 0 to 9: ")
        x = IO.ReadLine()
        x_as_int()

        IO.WriteLine("Enter your name: ")
        name = IO.ReadLine()

        For i = 0 To x Step 2
            IO.WriteLine("Hello " + name)
        EndFor
    EndWhile
EndSub

main()

AST

The output of this source code is:

+---------------------------------------+
| ----- Run source_code/source.sb ----- |
+---------------------------------------+

Enter a number from 0 to 9:
|> 8
Enter your name:
|> Federico
Hello Federico
Hello Federico
Hello Federico
Hello Federico

Example using Library, Array and Goto statements [source_code/first_prog.sb]

Sub init_value_as_int
  If (init_value = "1") Then init_value = 1 EndIf
  If (init_value = "2") Then init_value = 2 EndIf
  If (init_value = "3") Then init_value = 3 EndIf
  If (init_value = "4") Then init_value = 4 EndIf
  If (init_value = "5") Then init_value = 5 EndIf
  If (init_value = "6") Then init_value = 6 EndIf
  If (init_value = "7") Then init_value = 7 EndIf
  If (init_value = "8") Then init_value = 8 EndIf
  If (init_value = "9") Then init_value = 9 EndIf
EndSub

Sub ArrayInit
  For i = 0 To 3
      For j = 0 To 3
          my_vec[i][j] = init_value
      EndFor
  EndFor
EndSub

Sub ArrayIncrement
  For i = 0 To 3
      For j = 0 To 3
          my_vec[i][j] = my_vec[i][j] + 1
      EndFor
  EndFor
EndSub

Sub Main
  my_vec[2][2] = 0
  IO.WriteLine(my_vec)

  count = 0
  LabelFor5:
  IO.WriteLine(count)

  IO.WriteLine("Enter the value with which you want to initialize the array: ")
  init_value = IO.ReadLine()
  If (String.Length(init_value) > 1) Then
      IO.WriteLine("You entered more than one character. Only the first character will be used.")
      init_value = String.Substr(init_value, 0, 1)
  EndIf
  init_value_as_int()

  ArrayInit()
  IO.WriteLine(my_vec)

  ArrayIncrement()
  IO.WriteLine(my_vec)

  count = count + 1
  If (count < 5) Then
      Goto LabelFor5
  EndIf

  Goto End

  While (my_vec[2][2] < 10)
      ArrayIncrement()
      IO.WriteLine(my_vec)
  EndWhile
EndSub

Main()

End:
  IO.WriteLine("End of program.")

Example using nested Goto [source_code/second_prog.sb]

a = 1

Loop1:
  IO.WriteLine("Loop1")

  Loop2:
      IO.WriteLine("Loop2")
      a = a + 1
      If (a < 10) Then
          Goto Loop2
      EndIf

  IO.WriteLine(a)
  a = a + Math.Sqrt(a)
  IO.WriteLine(a)

  If (a > 100) Then
      Goto End
  EndIf

Goto Loop1


End:
  IO.WriteLine("End")

Parsing errors and warnings are displayed as follows:

Project directory structure

.
├── source_code
│   ├── ...
└── src
    ├── abstract_syntax_tree
    │   ├── ...
    ├── error
    │   ├── ...
    ├── grammar
    │   ├── SmallerBasic.g4
    │   └── ...
    ├── interpreter
    │   ├── dispatch_table.py
    │   ├── global_memory.py
    │   ├── interpreter.py
    │   └── library
    │       └── ...
    ├── main.py
    └── utils
        └── ...

Overview

• source_code: This directory contains the source code files of SmallerBasic programming language.

• src: The main source code directory containing various subdirectories and files related to the interpreter and language implementation.

  • abstract_syntax_tree: This directory hold files related to constructing and manipulating the abstract syntax tree.

  • error: This directory there are files related to error handling and reporting within the interpreter.

  • grammar: This directory contain the grammar definition files, such as SmallerBasic.g4, which define the syntax and structure of the SmallerBasic language using ANTLR grammar notation.

  • interpreter: This is a crucial directory containing the implementation of the interpreter for the SmallerBasic language.

    • dispatch_table.py: This file contains the implementation of a dispatch table used for efficiently executing different language constructs.

    • global_memory.py: This file contains the code related to managing the global memory and variables within the interpreter.

    • interpreter.py: This is the main interpreter implementation that executes SmallerBasic programs by traversing the abstract syntax tree and performing actions based on the language constructs.

    • library: This directory contain the library files that provide built-in functions or utilities for SmallerBasic programs, for example IO, Math and String libraries.

• main.py: This is the entry point of your interpreter, where execution starts when running the interpreter.

• utils: This directory could hold utility files that are used throughout the project, for example the metaclass that colors prints.

Starting point working locally

Create and start a new virtual environment

source create_venv.sh venv

Start current virtual environment

source venv/bin/activate

Deactivate the current virtual environment

deactivate

Usage

Usage: smallbasic [OPTION] [FILE]
Run Smaller Basic program

Options:
  -h      display this help and exit
  -g      generate grammar
  -gas    generate grammar and run all files in source_code folder
  -as     run all files in source_code folder

Interpreter

Run a file

smallbasic <file>.sb

For example, you can ri-generate the grammar and run a file in source_code directory in the following way:

smallbasic -g source_code/source.sb

Generate grammar

antlr4 -Dlanguage=Python3 -visitor src/grammar/SmallerBasic.g4

• Requirements: the same or greater java version used to compile the antlr4 jar. (in our case java-18-openjdk-amd64)

• Change version of java: update-alternatives --config java.

• antlr4 is an alias generated by the create_venv.sh file.

Run a file using python3 interpreter

python3 -m src.main source_code/<file>.sb

Contributing

Contributions to this project are welcome! If you have any suggestions, improvements, or bug fixes, feel free to submit a pull request.

License

This repository is licensed under the GNU General Public License (GPL). Please review the license file provided in the repository for more information regarding the terms and conditions of the GPL license.

Contact

• Email: [federico.bruzzone.i@gmail.com] or [federico.bruzzone@studenti.unimi.it]