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use crate::errors::{report, Error};
use crate::parser::{self, Expr, Literal};
use crate::scanner::{self, Token, TokenKind};
// Run some Lox code and print it to stdout
pub fn run(code: &str) {
let chars: Vec<char> = code.chars().collect();
match scanner::scan(&chars) {
Ok(tokens) => {
print_tokens(&tokens);
match parser::parse(tokens) {
Ok(expr) => {
println!("Expression:\n{:?}", expr);
println!("Result: {:?}", eval(&expr));
}
Err(errors) => report_errors(errors),
}
}
Err(errors) => report_errors(errors),
}
}
fn print_tokens<'a>(tokens: &Vec<Token<'a>>) {
println!("Tokens:");
for token in tokens {
println!("{:?}", token);
}
}
fn report_errors(errors: Vec<Error>) {
for error in errors {
report(&error);
}
}
// Tree-walk interpreter
fn eval_truthy(lit: &Literal) -> bool {
match lit {
Literal::Nil => false,
Literal::Boolean(b) => *b,
_ => true,
}
}
fn eval_unary<'a>(expr: &parser::Unary<'a>) -> Literal {
let right = eval(&*expr.right);
match (&expr.operator.kind, right) {
(TokenKind::Minus, Literal::Number(num)) => Literal::Number(-num),
(TokenKind::Bang, right) => Literal::Boolean(!eval_truthy(&right)),
_ => unimplemented!("no handling of type errors"),
}
}
fn eval_binary<'a>(expr: &parser::Binary<'a>) -> Literal {
let left = eval(&*expr.left);
let right = eval(&*expr.right);
match (&expr.operator.kind, left, right) {
// Numeric
(TokenKind::Minus, Literal::Number(l), Literal::Number(r)) => Literal::Number(l - r),
(TokenKind::Slash, Literal::Number(l), Literal::Number(r)) => Literal::Number(l / r),
(TokenKind::Star, Literal::Number(l), Literal::Number(r)) => Literal::Number(l * r),
(TokenKind::Plus, Literal::Number(l), Literal::Number(r)) => Literal::Number(l + r),
// Strings
(TokenKind::Plus, Literal::String(l), Literal::String(r)) => {
Literal::String(format!("{}{}", l, r))
}
// Comparators (on numbers only?)
(TokenKind::Greater, Literal::Number(l), Literal::Number(r)) => Literal::Boolean(l > r),
(TokenKind::GreaterEqual, Literal::Number(l), Literal::Number(r)) => {
Literal::Boolean(l >= r)
}
(TokenKind::Less, Literal::Number(l), Literal::Number(r)) => Literal::Boolean(l < r),
(TokenKind::LessEqual, Literal::Number(l), Literal::Number(r)) => Literal::Boolean(l <= r),
// Equality
(TokenKind::Equal, l, r) => Literal::Boolean(l == r),
(TokenKind::BangEqual, l, r) => Literal::Boolean(l != r),
_ => unimplemented!("type errors unhandled"),
}
}
fn eval<'a>(expr: &Expr<'a>) -> Literal {
match expr {
Expr::Literal(lit) => lit.clone(),
Expr::Grouping(grouping) => eval(&*grouping.0),
Expr::Unary(unary) => eval_unary(unary),
Expr::Binary(binary) => eval_binary(binary),
}
}
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