gabelang 3.1.0

use std::io::{self, BufRead, Write};
use crate::evaluator::Runtime;
use crate::parser::Parser;

/// The repl text that greets the user
pub static REPLGREETING: &'static str = r"WELCOME TO
   _____       _          _                   
  / ____|     | |        | |                  
 | |  __  __ _| |__   ___| | __ _ _ __   __ _ 
 | | |_ |/ _` | '_ \ / _ \ |/ _` | '_ \ / _` |
 | |__| | (_| | |_) |  __/ | (_| | | | | (_| |
  \_____|\__,_|_.__/ \___|_|\__,_|_| |_|\__, |
                                         __/ |
                                        |___/ 
GABELANG IS A HIGH LEVEL, INTERPRETTED, GARBAGE COLLECTED, PROGRAMMING LANGUAGE THAT SUPPORTS
ARRAYS,OBJECTS, AND FIRST CLASS AND HIGHER ORDER FUNCTIONS

TRY DECLARING VARIABLES LIKE THIS
>> let i = { a: [5], b: 3 * 3 };

TRY DECLARING FUNCTIONS LIKE THIS
>> fn double_and_abs(num) {if num > 0 {return num * 2;} else {return num * -2;}}

TYPING AN EXPRESSION INSTEAD OF A STATEMENT WILL PRINT THE EVALUATION OF THE STATEMENT
>> double_and_abs(i.b)
18";

/// Starts the gabelang repl in an isolated environment, which greets the user and allows the user to run arbitrary gabelang code
///
/// The repl runs until forcefully terminated and prints to stdout and takes input from stdin.
pub fn start() {
    println!("{REPLGREETING}");
    print!(">> ");
    io::stdout().flush().unwrap();
    let stdin = io::stdin();
    let mut env = Runtime::new();
    for line in stdin.lock().lines() {
        let program_ast = Parser::new(&line.unwrap()).parse_program();
        let program = match program_ast {
            Ok(program) => program,
            Err(err_msg) => {
                println!("{err_msg}");
                print!(">> ");
                io::stdout().flush().unwrap();
                continue;
            }
        };
        match env.run_program(&program) {
            Ok(object) => {
                if object.is_some() {
                    println!("{object}");
                }
            },
            Err(err) => println!("{err}")
        };
        print!(">> ");
        io::stdout().flush().unwrap();
    }
}