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ScriptLang

This is a simple scripting language written in C++17. This project was a way to improve my knowledge on developing programming languages, stack-based virtual machines and even C++. In fact, the goal of this project is not to create a fast and efficient scripting programming language, but to learn how to parse and compile source code and how to output detailed error messages when one of these steps fails.

defun fib(n) {
      if n <= 1 { return 1; }
      return fib(n - 1) + fib(n - 2);
}

print fib(9);

// Output: 34

For this project I took inspiration from these projects:

Features

  • Global and local variables

  • If statements

  • While loop

  • Functions

  • Print statement

  • All classical binary operations + exponentiation

Data Types

  • Nil

  • Booleans

  • Strings

  • Numbers

Warning

This language don't have structs or similar construcuts and don't support closures.

Grammar

declaration ::= function-decl
            | variable-decl

variable-decl ::= 'let' IDENTIFIER '=' expression ';'

function-parameters ::= '(' IDENTIFIER (',' IDENTIFIER)* ')'
function-decl ::= 'defun' IDENTIFIER function-parameters block

block ::= '{' declaration* '}'

statement ::= if-statement
          | expression-statement
          | while-statement
          | for-statement
          | break-statement
          | continue-statement
          | return-statement
          | block

print-statement ::= 'print' expression ';'
if-statement ::= 'if' expression block ('else' block)*
while-statement ::= 'while' expression block
break-statement ::= 'break' ';'
continue-statement ::= 'continue' ';'
return-statement ::= 'return' expression? ';'

expression-statement ::= expression ';'

expression ::= assignment 
assignment ::= IDENTIFIER '=' assignment | logic-or
logic-or ::= logic-and ('or' logic-and)*
logic-and ::= equality ('and' equality)*
equality ::= comparison (('==' | '!=') comparison)*
comparison ::= term (('>' | '<' | '<=' | '>=') term)*
term ::= factor (('+' | '-' factor)*
factor ::= unary (('*' | '/' unary)*
unary ::= ('-' | '+' | 'not') unary | exponent
exponent ::= call ('**' factor)*

call-arguments ::= expression (',' expression)*
call ::= primary ( '(' call-arguments+ ')'
primary ::= NUMBER_LITERAL 
        | STRING_LITERAL 
        | IDENTIFIER
        | 'true'
        | 'false'
        | 'nil'
        | '(' expression ')'