gistfile1.txt

// Directives
#![allow(unused_must_use)]

// Imports
use std::slice::Iter;
use std::iter::Peekable;

/// Takes a string of chars and returns a vector of tokens.
fn tokenize(chars:&str) -> Vec<String> {

    chars.replace("(", " ( ")
        .replace(")", " ) ")
        .split_whitespace()
        .filter(|s| !(s.is_empty()))
        .map(|s| s.to_string())
        .collect()
}
/// Reads an expression from a sequence of tokens.
fn read_from_tokens(tokens: &mut Peekable<Iter<String>>) -> Data {
    
    if tokens.len() == 0 {
        panic!("Unexpected EOF while parsing.");
    }

    let token = tokens.next().unwrap();

    if token == "(" {
        let mut l = Nil;
        while *tokens.peek().expect("Syntax error! Expected ')'") != ")" {
            l = read_from_tokens(tokens).cons(l);
        }
        tokens.next();
        return l.nreverse();
    }
    
    match token.parse::<f32>() {
        Ok(f) => return Float(f),
        _ => {;}
    }
   
    return Symbol(token.to_string())
}

fn parse(program:&str) -> Data {
    return read_from_tokens(&mut tokenize(program).iter().peekable());
}