Tiny BASIC Interpreter

A step-bu-step Tiny BASIC interpreter. Starting with lexer - educational and open for contributions!

What has been implemented now and what is planned

• Lexical Analyzer (Lexer)
• Syntax Analyzer (Parser)
  • Recursive descent parsing
  • Abstract Syntax Tree (AST)
• Interpreter
  • Expression evaluation
  • Variable assignment (LET)
  • Output (PRINT)
  • Conditional statements (IF-THEN)
  • Loops (FOR-NEXT)
  • User input (INPUT)

Example

10 LET A = 5 + 2 * (2 * 1) * (5 * 1)
20 LET B = 3 * 3 + 2
30 PRINT A
40 PRINT B

Lexer Output

Token: Number      	    -> '10'
Token: Keyword     	    -> 'LET'
Token: Identifier  	    -> 'A'
Token: Equal       	    -> '='
Token: Number      	    -> '5'
Token: Plus        	    -> '+'
Token: Number      	    -> '2'
Token: Mult        	    -> '*'
Token: LeftParenthesis	-> '('
Token: Number      	    -> '2'
Token: Mult        	    -> '*'
Token: Number      	    -> '1'
Token: RightParenthesis	-> ')'
Token: Mult        	    -> '*'
Token: LeftParenthesis	-> '('
Token: Number      	    -> '5'
Token: Mult        	    -> '*'
Token: Number      	    -> '1'
Token: RightParenthesis	-> ')'
Token: Number      	    -> '20'
Token: Keyword     	    -> 'PRINT'
Token: Identifier  	    -> 'A'

Parser Output (AST)

LetStmt: A=
  BinaryExpr: +
    Literal: 5
    BinaryExpr: *
      BinaryExpr: *
        Literal: 2
        BinaryExpr: *
          Literal: 2
          Literal: 1
      BinaryExpr: *
        Literal: 5
        Literal: 1

PrintStmt: 
  Variable: A

Program Execution

Execute: 
25
11
End of program.

Quick Start

git clone https://github.com/varvarian1/Tiny-BASIC.git
cd Tiny-BASIC
mkdir build && cd build
cmake ..
cmake --build .
cd ../output
./basic ../examples/test.bas