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|
use crate::errors::{Error, ErrorKind};
use crate::parser::{self, Declaration, Expr, Literal, Program, Statement};
use crate::scanner::TokenKind;
use std::collections::HashMap;
// Tree-walk interpreter
#[derive(Debug, Default)]
struct Environment {
values: HashMap<String, Literal>,
}
impl Environment {
fn define(&mut self, name: &str, value: Literal) {
self.values.insert(name.into(), value);
}
fn get(&self, name: &parser::Variable) -> Result<Literal, Error> {
if let TokenKind::Identifier(ident) = &name.0.kind {
return self
.values
.get(ident)
.map(Clone::clone)
.ok_or_else(|| Error {
line: name.0.line,
kind: ErrorKind::UndefinedVariable(ident.into()),
});
}
Err(Error {
line: name.0.line,
kind: ErrorKind::InternalError("unexpected identifier kind".into()),
})
}
}
#[derive(Debug, Default)]
pub struct Interpreter {
globals: Environment,
}
impl Interpreter {
fn interpret_stmt<'a>(&self, stmt: &Statement<'a>) -> Result<(), Error> {
match stmt {
Statement::Expr(expr) => {
self.eval(expr)?;
}
Statement::Print(expr) => {
let result = self.eval(expr)?;
println!("{:?}", result)
}
}
Ok(())
}
fn interpret_var<'a>(&mut self, var: &parser::Var<'a>) -> Result<(), Error> {
if let TokenKind::Identifier(ident) = &var.name.kind {
let init = var.initialiser.as_ref().ok_or_else(|| Error {
line: var.name.line,
kind: ErrorKind::InternalError("missing variable initialiser".into()),
})?;
self.globals.define(ident, self.eval(init)?);
return Ok(());
}
Err(Error {
line: var.name.line,
kind: ErrorKind::InternalError("unexpected identifier kind".into()),
})
}
pub fn interpret<'a>(&mut self, program: &Program<'a>) -> Result<(), Error> {
for decl in program {
match decl {
Declaration::Stmt(stmt) => self.interpret_stmt(stmt)?,
Declaration::Var(var) => self.interpret_var(var)?,
}
}
Ok(())
}
fn eval<'a>(&self, expr: &Expr<'a>) -> Result<Literal, Error> {
match expr {
Expr::Literal(lit) => Ok(lit.clone()),
Expr::Grouping(grouping) => self.eval(&*grouping.0),
Expr::Unary(unary) => self.eval_unary(unary),
Expr::Binary(binary) => self.eval_binary(binary),
Expr::Variable(var) => self.globals.get(var),
}
}
fn eval_unary<'a>(&self, expr: &parser::Unary<'a>) -> Result<Literal, Error> {
let right = self.eval(&*expr.right)?;
match (&expr.operator.kind, right) {
(TokenKind::Minus, Literal::Number(num)) => Ok(Literal::Number(-num)),
(TokenKind::Bang, right) => Ok(Literal::Boolean(!eval_truthy(&right))),
(op, right) => Err(Error {
line: expr.operator.line,
kind: ErrorKind::TypeError(format!(
"Operator '{:?}' can not be called with argument '{:?}'",
op, right
)),
}),
}
}
fn eval_binary<'a>(&self, expr: &parser::Binary<'a>) -> Result<Literal, Error> {
let left = self.eval(&*expr.left)?;
let right = self.eval(&*expr.right)?;
let result = 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),
(op, left, right) => {
return Err(Error {
line: expr.operator.line,
kind: ErrorKind::TypeError(format!(
"Operator '{:?}' can not be called with arguments '({:?}, {:?})'",
op, left, right
)),
})
}
};
Ok(result)
}
}
// Interpreter functions not dependent on interpreter-state.
fn eval_truthy(lit: &Literal) -> bool {
match lit {
Literal::Nil => false,
Literal::Boolean(b) => *b,
_ => true,
}
}
|
