Interpreter

Interpreter written in Bison, Flex and C++ for simple custom programming language.

Language Syntax

Instructions

• assignment - variable_name = equation
• Print
  • PRINT(equation)
  • PRINT("text")
• IF
  • IF(equation comparator equation) instruction
  • IF(equation comparator equation) { instructions }
• WHILE
  • WHILE(variable, assignment) instruction
  • WHILE(variable, assignment) { instructions }

Symbols Explanation

• equation
  • single number,
  • single variable,
  • +-*/ - addition, subtraction, multiplication and division of variables/numbers,
  • ^ - variable/number to the power of variable/number.
• text - character string (ASCII signs from 32 to 126)
• comparator - one of these words: ==, !=, > , >=, <, <=.
• instruction - single instruction.
• instructions - multiple instructions.

WHILE Explanation

• first argument - control variable for loop. Breaks the loop upon reaching the value of zero.
• second argument - assignment executed on first argument.

Mode Flags

This program uses flags to run in normal mode or debug mode. Possible run scenarios:

• INTERPRETER -n
• INTERPRETER -d
• INTERPRETER -flag < program.txt

-n - runs program in normal mode.
-d - runs program in debug mode.
-flag - any of above flags (used only for example).

Capabilities

• debug mode (enabled with flag),
• real numbers operations,
• print instruction working for numbers and texts,
• order of operations (eg. multiplication before addition),
• negative numbers and negated variables,
• nested instructions (IFs in WHILEs and conversely),
• single-line and multi-line comments (C/C++ style)
• error detection (undeclared variable, missing semi-colon, wrong WHILE second argument),
• line and column tracking (used in error detection).

Example Code

var_1 = 3^5;
var_2 = -var_1 + 3 + 120 + 4*5/3;

//This is a commnet (interpreter ignores it)
/*
	This is also ignored
*/

PRINT("If test");
a = 10.5^3;
b = 3 * 10^2/2 + 18/2*3 - 1;

IF ( a >= 10 ) { 
	IF( a < 10000 ){
		print( b );
	};
	print( a );
};
it = -10;
check = 1;

PRINT("MAIN LOOP");

WHILE ( it, it=it+1 ) { 
	IF( check < 128 ) {
		check = check * 2;
		it2 = 2;
		
		PRINT("");
		PRINT("INTERNAL LOOP");
		
		WHILE (it2, it2 = it2 - 1){ 
			PRINT(check);
			IF( it2 == 1 ){
				check = check + 1;
				PRINT(it2);
			};
		};
		IF( it2 == 0 ){
			it2 = it2 + 3*check;
			PRINT(it2);
		};
	};
	IF( check >= 128 ) {
		PRINT("");
		PRINT("IF false!");
	};
};

PRINT("");
PRINT("Print check:");
print(check);

*code written in language defined for the interpreter

Requirements

To compile this program you need:

• C++ compiler
• Flex binaries
• Bison binaries (may require additional binaries)

Software used for this project

• MinGW - Minimalist GNU for Windows
• Flex for Windows
• Bison for Windows
• Visual Studio Code with Lex Flex Yacc Bison plugin

Console commands (used by me on Windows)

1. bison.exe -dy interpreter.y
2. flex.exe interpreter.lex
3. g++.exe y.tab.c lex.yy.c -o "your_exe_name.exe"

Thanks

• SuddenlyPineapple gave the idea for using enums in switch in execute_instruction() function.