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https://github.com/chermehdi/comet

A programming language implementation in Go.
https://github.com/chermehdi/comet

educational golang interpreter programming-language

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A programming language implementation in Go.

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README 

        
![Comet build status](https://github.com/chermehdi/comet/workflows/Go/badge.svg?branch=master)



# Comet programming language 



![comet programming language](./comet.png)



- A simple programming language aimed to be used for educational purposes, and to teach how programming language interpreters

can be made.



- Since it's made for educational purposes, all the parts that make a lexer are made from scratch `lexer`, `parser` and `evaluator`.



## Language Example 



- The language is a `C` derived language, with the ability to create `structs` as complex types, and declare functions as First class values.

- The language is dynamically typed, to make it easier to implement



```

// variable declarations

var a = 10

var c = "some string"

var arrayValue = [1, 2, 3]



func add(a, b) {

    return a + b

}



func isBigger(a, b) {

    return a > b

}



struct Data { 

    func init(a, b, c) {

        this.a = a

        this.c = a + b

    }

    

    func doSomething() {

        return a + c 

    } 

}

// STRUCT_DECL: struct Identifier BLOCK

// BLOCK: { functions* } 



// 

// var data = new Data(a, b, c)



// data.doSomething()



// Object declaration

var object = new()

object.field = "field value"



object.method = func(a) {

    return a * 2

}



var value = object.call()



var loopConstruct = func(a, b) {

    var sum = 0

    for i = 1; i < 10; i += 1 {

        sum += i

    }

    return sum

}



var conditional = func(a, b) {

}

// a program entrypoint

func main() {

    var c = a + add(1, 4)

    // builtin functions

    println(c)

}

```



## Grammar



- Below are the grammar rules for the language (it can be left recursive, we will deal with it at some point)



```

// Parser rules

grammar Comet;



comet:

    function_declaration+ EOF

    ;



function_declaration:

    'func' IDENTIFIER'('parameterless')' '{' statements '}' # functionDeclaration

    ;



parameterless:

    parameters*

    ;



parameters:

    IDENTIFIER(','IDENTIFIER)* | expression (','expression)*

    ;



statements:

    statement*

    ;



statement:

    assignment_statement                      # assignment

    | if_statement                            # ifStatement

    | return_statement                        # returnStatement

    | for_loop                                # forLoop

    ;



assignment_statement:

    IDENTIFIER '=' expression

    ;



if_statement:

    'if' '('expression')' '{' statements '}' ('else' '{' statements '}')?

    ;



return_statement:

    'return' expression

    ;



for_loop:

    'for' '('expression')' '{' statements '}'

    ;



# struct and object declaration to be defined later

# struct_statement:

#    'struct' IDENTIFIER '{' FIELD* '}'



expression:

    function_call

    | IDENTIFIER

    | STRING 

    | NUMBER 

    | BOOL 

    | string_concat

    | math_expression

    | array_declaration

    ;



array_declaration:

    '['(expression (','expression)*)?']'



function_call:

    IDENTIFIER '('parameterless')'

    ;



string_concat:

    STRING ('+' STRING)*

    ;



math_expression:

    term (('+' | '-') term)*

    ;



term:

    factor (('*' | '/') factor)*

    ;



factor:

    IDENTIFIER

    | string

    | number

    | '('expression')'

    ;



// Lexer rules



WS : [ \t\r\n\u000C]+ -> skip;

COMMENT : '/*' .*? '*/' -> skip;

LINE_COMMENT : '//' ~[\r\n]* -> skip;

IDENTIFIER: ('_'|LETTER)(LETTER|DIGIT|'_')*;

NUMBER: ('-' | '+')? (([1-9][0-9]*) | ([0-9]));

OPERATOR: '+' | '-' | '*' | '/' | '%' | '!';

fragment DIGIT: [0-9];

BOOL: 'true' | 'false';

LETTER: [a-zA-Z];

STRING: '"' ~('\r' | '\n' | '"')* '"' ;

```



## Tasks



These are the list of the tasks that I think should be done before having the first release:



- [x] Add variable declarations

- [x] Add conditionals

- [ ] Add Proper scoping

- [ ] Add support for loops 

- [ ] Add Arrays support

- [ ] Add Comments support

- [ ] Add Hash support

- [ ] Add import modules support

- [ ] Add testing framework 

- [ ] Add build system

- [ ] Add a standard library



## Contribution



- Feel free to submit new issues, or pull requests.