666 lines
22 KiB
Rust
666 lines
22 KiB
Rust
//! Expression evaluator and statement interpreter.
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//!
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//! To interpret a piece of AbleScript code, you first need to
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//! construct an [ExecEnv], which is responsible for storing the stack
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//! of local variable and function definitions accessible from an
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//! AbleScript snippet. You can then call [ExecEnv::eval_stmts] to
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//! evaluate or execute any number of expressions or statements.
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#![deny(missing_docs)]
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use std::{
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cell::RefCell,
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collections::{HashMap, VecDeque},
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io::{stdin, stdout, Read, Write},
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ops::Range,
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process::exit,
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rc::Rc,
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};
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use rand::random;
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use crate::{
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ast::{Expr, ExprKind, Iden, Stmt, StmtKind},
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base_55,
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consts::{self, ablescript_consts},
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error::{Error, ErrorKind},
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variables::{Functio, Value, Variable},
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};
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/// An environment for executing AbleScript code.
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pub struct ExecEnv {
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/// The stack, ordered such that `stack[stack.len() - 1]` is the
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/// top-most (newest) stack frame, and `stack[0]` is the
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/// bottom-most (oldest) stack frame.
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stack: Vec<Scope>,
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/// The `read` statement maintains a buffer of up to 7 bits,
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/// because input comes from the operating system 8 bits at a time
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/// (via stdin) but gets delivered to AbleScript 3 bits at a time
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/// (via the `read` statement). We store each of those bits as
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/// booleans to facilitate easy manipulation.
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read_buf: VecDeque<bool>,
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}
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/// A set of visible variable and function definitions in a single
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/// stack frame.
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struct Scope {
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/// The mapping from variable names to values.
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variables: HashMap<String, Variable>,
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}
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impl Default for Scope {
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fn default() -> Self {
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Self {
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variables: ablescript_consts(),
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}
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}
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}
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/// The reason a successful series of statements halted.
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enum HaltStatus {
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/// We ran out of statements to execute.
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Finished,
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/// A `break` statement occurred at the given span, and was not
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/// caught by a `loop` statement up to this point.
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Break(Range<usize>),
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/// A `hopback` statement occurred at the given span, and was not
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/// caught by a `loop` statement up to this point.
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Hopback(Range<usize>),
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}
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/// The number of bits the `read` statement reads at once from
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/// standard input.
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pub const READ_BITS: u8 = 3;
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impl ExecEnv {
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/// Create a new Scope with no predefined variable definitions or
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/// other information.
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pub fn new() -> Self {
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Self {
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// We always need at least one stackframe.
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stack: vec![Default::default()],
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read_buf: Default::default(),
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}
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}
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/// Execute a set of Statements in the root stack frame. Return an
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/// error if one or more of the Stmts failed to evaluate, or if a
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/// `break` or `hopback` statement occurred at the top level.
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pub fn eval_stmts(&mut self, stmts: &[Stmt]) -> Result<(), Error> {
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match self.eval_stmts_hs(stmts, false)? {
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HaltStatus::Finished => Ok(()),
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HaltStatus::Break(span) | HaltStatus::Hopback(span) => Err(Error {
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// It's an error to issue a `break` outside of a
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// `loop` statement.
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kind: ErrorKind::TopLevelBreak,
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span,
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}),
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}
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}
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/// The same as `eval_stmts`, but report "break" and "hopback"
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/// exit codes as normal conditions in a HaltStatus enum, and
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/// create a new stack frame if `stackframe` is true.
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///
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/// `interpret`-internal code should typically prefer this
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/// function over `eval_stmts`.
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fn eval_stmts_hs(&mut self, stmts: &[Stmt], stackframe: bool) -> Result<HaltStatus, Error> {
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let init_depth = self.stack.len();
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if stackframe {
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self.stack.push(Default::default());
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}
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let mut final_result = Ok(HaltStatus::Finished);
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for stmt in stmts {
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final_result = self.eval_stmt(stmt);
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if !matches!(final_result, Ok(HaltStatus::Finished)) {
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break;
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}
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}
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if stackframe {
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self.stack.pop();
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}
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// Invariant: stack size must have net 0 change.
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debug_assert_eq!(self.stack.len(), init_depth);
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final_result
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}
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/// Evaluate an Expr, returning its value or an error.
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fn eval_expr(&self, expr: &Expr) -> Result<Value, Error> {
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use crate::ast::BinOpKind::*;
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use crate::ast::ExprKind::*;
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use Value::*;
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Ok(match &expr.kind {
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BinOp { lhs, rhs, kind } => {
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let lhs = self.eval_expr(lhs)?;
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let rhs = self.eval_expr(rhs)?;
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match kind {
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// Arithmetic operators.
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Add | Subtract | Multiply | Divide => {
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let lhs = lhs.to_i32();
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let rhs = rhs.to_i32();
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let res = match kind {
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Add => lhs.checked_add(rhs),
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Subtract => lhs.checked_sub(rhs),
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Multiply => lhs.checked_mul(rhs),
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Divide => lhs.checked_div(rhs),
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_ => unreachable!(),
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}
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.unwrap_or(consts::ANSWER);
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Int(res)
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}
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// Numeric comparisons.
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Less | Greater => {
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let lhs = lhs.to_i32();
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let rhs = rhs.to_i32();
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let res = match kind {
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Less => lhs < rhs,
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Greater => lhs > rhs,
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_ => unreachable!(),
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};
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Bool(res)
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}
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// General comparisons.
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Equal | NotEqual => {
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let res = match kind {
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Equal => lhs == rhs,
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NotEqual => lhs != rhs,
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_ => unreachable!(),
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};
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Bool(res)
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}
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// Logical connectives.
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And | Or => {
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let lhs = lhs.to_bool();
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let rhs = rhs.to_bool();
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let res = match kind {
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And => lhs && rhs,
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Or => lhs || rhs,
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_ => unreachable!(),
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};
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Bool(res)
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}
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}
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}
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Not(expr) => Bool(!self.eval_expr(expr)?.to_bool()),
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Literal(value) => value.clone(),
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ExprKind::Cart(members) => Value::Cart(
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members
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.iter()
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.map(|(value, key)| {
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self.eval_expr(value).and_then(|value| {
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self.eval_expr(key)
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.map(|key| (key, Rc::new(RefCell::new(value))))
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})
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})
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.collect::<Result<HashMap<_, _>, _>>()?,
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),
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Index { cart, index } => {
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let cart = self.eval_expr(cart)?;
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let index = self.eval_expr(index)?;
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// TODO: this probably shouldn't be cloned
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cart.index(&index).borrow().clone()
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}
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// TODO: not too happy with constructing an artificial
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// Iden here.
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Variable(name) => self.get_var(&Iden {
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iden: name.to_owned(),
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span: expr.span.clone(),
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})?,
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})
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}
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/// Perform the action indicated by a statement.
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fn eval_stmt(&mut self, stmt: &Stmt) -> Result<HaltStatus, Error> {
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match &stmt.kind {
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StmtKind::Print(expr) => {
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println!("{}", self.eval_expr(expr)?);
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}
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StmtKind::Var { iden, init } => {
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let init = match init {
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Some(e) => self.eval_expr(e)?,
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None => Value::Nul,
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};
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self.decl_var(&iden.iden, init);
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}
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StmtKind::Functio { iden, params, body } => {
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self.decl_var(
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&iden.iden,
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Value::Functio(Functio::AbleFunctio {
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params: params.iter().map(|iden| iden.iden.to_string()).collect(),
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body: body.block.to_owned(),
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}),
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);
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}
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StmtKind::BfFunctio {
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iden,
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tape_len,
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code,
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} => {
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self.decl_var(
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&iden.iden,
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Value::Functio(Functio::BfFunctio {
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instructions: code.to_owned(),
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tape_len: tape_len
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.as_ref()
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.map(|tape_len| self.eval_expr(tape_len).map(|v| v.to_i32() as usize))
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.unwrap_or(Ok(crate::brian::DEFAULT_TAPE_SIZE_LIMIT))?,
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}),
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);
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}
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StmtKind::If { cond, body } => {
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if self.eval_expr(cond)?.to_bool() {
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return self.eval_stmts_hs(&body.block, true);
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}
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}
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StmtKind::Call { expr, args } => {
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let func = self.eval_expr(expr)?;
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if let Value::Functio(func) = func {
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self.fn_call(func, args, &stmt.span)?;
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} else {
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// Fail silently for now.
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}
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}
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StmtKind::Loop { body } => loop {
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let res = self.eval_stmts_hs(&body.block, true)?;
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match res {
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HaltStatus::Finished => {}
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HaltStatus::Break(_) => break,
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HaltStatus::Hopback(_) => continue,
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}
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},
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StmtKind::Assign { iden, value } => {
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let value = self.eval_expr(value)?;
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self.get_var_mut(iden)?.value.replace(value);
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}
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StmtKind::Break => {
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return Ok(HaltStatus::Break(stmt.span.clone()));
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}
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StmtKind::HopBack => {
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return Ok(HaltStatus::Hopback(stmt.span.clone()));
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}
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StmtKind::Melo(iden) => {
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self.get_var_mut(iden)?.melo = true;
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}
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StmtKind::Rlyeh => {
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// Maybe print a creepy error message or something
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// here at some point. ~~Alex
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exit(random());
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}
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StmtKind::Rickroll => {
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stdout()
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.write_all(include_str!("rickroll").as_bytes())
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.expect("Failed to write to stdout");
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}
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StmtKind::Read(iden) => {
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let mut value = 0;
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for _ in 0..READ_BITS {
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value <<= 1;
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value += self.get_bit()? as i32;
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}
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self.get_var_mut(iden)?.value.replace(Value::Int(value));
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}
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}
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Ok(HaltStatus::Finished)
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}
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/// Call a function with the given arguments (i.e., actual
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/// parameters). If the function invocation fails for some reason,
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/// report the error at `span`.
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fn fn_call(&mut self, func: Functio, args: &[Expr], span: &Range<usize>) -> Result<(), Error> {
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// Arguments that are ExprKind::Variable are pass by
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// reference; all other expressions are pass by value.
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let args = args
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.iter()
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.map(|arg| {
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if let ExprKind::Variable(name) = &arg.kind {
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self.get_var_rc(&Iden {
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iden: name.to_owned(),
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span: arg.span.clone(),
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})
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} else {
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self.eval_expr(arg).map(|v| Rc::new(RefCell::new(v)))
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}
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})
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.collect::<Result<Vec<_>, Error>>()?;
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match func {
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Functio::BfFunctio {
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instructions,
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tape_len,
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} => {
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let mut input: Vec<u8> = vec![];
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for arg in args {
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arg.borrow().bf_write(&mut input);
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}
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let mut output = vec![];
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crate::brian::Interpreter::from_ascii_with_tape_limit(
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&instructions,
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&input as &[_],
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tape_len,
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)
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.interpret_with_output(&mut output)
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.map_err(|e| Error {
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kind: ErrorKind::BfInterpretError(e),
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span: span.to_owned(),
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})?;
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stdout()
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.write_all(&output)
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.expect("Failed to write to stdout");
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}
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Functio::AbleFunctio { params, body } => {
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if params.len() != args.len() {
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return Err(Error {
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kind: ErrorKind::MismatchedArgumentError,
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span: span.to_owned(),
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});
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}
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self.stack.push(Default::default());
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for (param, arg) in params.iter().zip(args.iter()) {
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self.decl_var_shared(param, arg.to_owned());
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}
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let res = self.eval_stmts_hs(&body, false);
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self.stack.pop();
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res?;
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}
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}
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Ok(())
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}
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/// Get a single bit from the bit buffer, or refill it from
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/// standard input if it is empty.
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fn get_bit(&mut self) -> Result<bool, Error> {
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const BITS_PER_BYTE: u8 = 8;
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if self.read_buf.is_empty() {
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let mut data = [0];
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stdin().read_exact(&mut data)?;
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for n in (0..BITS_PER_BYTE).rev() {
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self.read_buf.push_back(((data[0] >> n) & 1) != 0);
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}
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}
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Ok(self
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.read_buf
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.pop_front()
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.expect("We just pushed to the buffer if it was empty"))
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}
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/// Get the value of a variable. Throw an error if the variable is
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/// inaccessible or banned.
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fn get_var(&self, name: &Iden) -> Result<Value, Error> {
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// One-letter names are reserved as base55 numbers.
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let mut chars = name.iden.chars();
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if let (Some(first), None) = (chars.next(), chars.next()) {
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return Ok(Value::Int(base_55::char2num(first)));
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}
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// Otherwise, search for the name in the stack from top to
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// bottom.
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match self
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.stack
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.iter()
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.rev()
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.find_map(|scope| scope.variables.get(&name.iden))
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{
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Some(var) => {
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if !var.melo {
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Ok(var.value.borrow().clone())
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} else {
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Err(Error {
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kind: ErrorKind::MeloVariable(name.iden.to_owned()),
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span: name.span.clone(),
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})
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}
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}
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None => Err(Error {
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kind: ErrorKind::UnknownVariable(name.iden.to_owned()),
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span: name.span.clone(),
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}),
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}
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}
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/// Get a mutable reference to a variable. Throw an error if the
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/// variable is inaccessible or banned.
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fn get_var_mut(&mut self, name: &Iden) -> Result<&mut Variable, Error> {
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// This function has a lot of duplicated code with `get_var`,
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// which I feel like is a bad sign...
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match self
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.stack
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.iter_mut()
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.rev()
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.find_map(|scope| scope.variables.get_mut(&name.iden))
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{
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Some(var) => {
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if !var.melo {
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Ok(var)
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} else {
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Err(Error {
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kind: ErrorKind::MeloVariable(name.iden.to_owned()),
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span: name.span.clone(),
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})
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}
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}
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None => Err(Error {
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kind: ErrorKind::UnknownVariable(name.iden.to_owned()),
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span: name.span.clone(),
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}),
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}
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}
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/// Get an Rc'd pointer to the value of a variable. Throw an error
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/// if the variable is inaccessible or banned.
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fn get_var_rc(&mut self, name: &Iden) -> Result<Rc<RefCell<Value>>, Error> {
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Ok(self.get_var_mut(name)?.value.clone())
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}
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/// Declare a new variable, with the given initial value.
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fn decl_var(&mut self, name: &str, value: Value) {
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self.decl_var_shared(name, Rc::new(RefCell::new(value)));
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}
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|
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/// Declare a new variable, with the given shared initial value.
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fn decl_var_shared(&mut self, name: &str, value: Rc<RefCell<Value>>) {
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self.stack
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.iter_mut()
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.last()
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.expect("Declaring variable on empty stack")
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.variables
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.insert(name.to_owned(), Variable { melo: false, value });
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}
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}
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#[cfg(test)]
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mod tests {
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use crate::ast::ExprKind;
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|
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use super::*;
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|
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#[test]
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fn basic_expression_test() {
|
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// Check that 2 + 2 = 4.
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let env = ExecEnv::new();
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assert_eq!(
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env.eval_expr(&Expr {
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kind: ExprKind::BinOp {
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lhs: Box::new(Expr {
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kind: ExprKind::Literal(Value::Int(2)),
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span: 1..1,
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}),
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rhs: Box::new(Expr {
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kind: ExprKind::Literal(Value::Int(2)),
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span: 1..1,
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}),
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kind: crate::ast::BinOpKind::Add,
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},
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span: 1..1
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})
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.unwrap(),
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Value::Int(4)
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)
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}
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|
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#[test]
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fn type_coercions() {
|
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// The sum of an integer and a boolean causes a boolean
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// coercion.
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let env = ExecEnv::new();
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assert_eq!(
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env.eval_expr(&Expr {
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kind: ExprKind::BinOp {
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lhs: Box::new(Expr {
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kind: ExprKind::Literal(Value::Int(2)),
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span: 1..1,
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}),
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rhs: Box::new(Expr {
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kind: ExprKind::Literal(Value::Bool(true)),
|
|
span: 1..1,
|
|
}),
|
|
kind: crate::ast::BinOpKind::Add,
|
|
},
|
|
span: 1..1
|
|
})
|
|
.unwrap(),
|
|
Value::Int(3)
|
|
);
|
|
}
|
|
|
|
#[test]
|
|
fn overflow_should_not_panic() {
|
|
// Integer overflow should throw a recoverable error instead
|
|
// of panicking.
|
|
let env = ExecEnv::new();
|
|
assert_eq!(
|
|
env.eval_expr(&Expr {
|
|
kind: ExprKind::BinOp {
|
|
lhs: Box::new(Expr {
|
|
kind: ExprKind::Literal(Value::Int(i32::MAX)),
|
|
span: 1..1,
|
|
}),
|
|
rhs: Box::new(Expr {
|
|
kind: ExprKind::Literal(Value::Int(1)),
|
|
span: 1..1,
|
|
}),
|
|
kind: crate::ast::BinOpKind::Add,
|
|
},
|
|
span: 1..1
|
|
})
|
|
.unwrap(),
|
|
Value::Int(42)
|
|
);
|
|
|
|
// And the same for divide by zero.
|
|
assert_eq!(
|
|
env.eval_expr(&Expr {
|
|
kind: ExprKind::BinOp {
|
|
lhs: Box::new(Expr {
|
|
kind: ExprKind::Literal(Value::Int(1)),
|
|
span: 1..1,
|
|
}),
|
|
rhs: Box::new(Expr {
|
|
kind: ExprKind::Literal(Value::Int(0)),
|
|
span: 1..1,
|
|
}),
|
|
kind: crate::ast::BinOpKind::Divide,
|
|
},
|
|
span: 1..1
|
|
})
|
|
.unwrap(),
|
|
Value::Int(42)
|
|
);
|
|
}
|
|
|
|
// From here on out, I'll use this function to parse and run
|
|
// expressions, because writing out abstract syntax trees by hand
|
|
// takes forever and is error-prone.
|
|
fn eval(env: &mut ExecEnv, src: &str) -> Result<Value, Error> {
|
|
let mut parser = crate::parser::Parser::new(src);
|
|
|
|
// We can assume there won't be any syntax errors in the
|
|
// interpreter tests.
|
|
let ast = parser.init().unwrap();
|
|
env.eval_stmts(&ast).map(|()| Value::Nul)
|
|
}
|
|
|
|
#[test]
|
|
fn variable_decl_and_assignment() {
|
|
// Functions have no return values, so use some
|
|
// pass-by-reference hacks to detect the correct
|
|
// functionality.
|
|
let mut env = ExecEnv::new();
|
|
|
|
// Declaring and reading from a variable.
|
|
eval(&mut env, "var foo = 32; var bar = foo + 1;").unwrap();
|
|
assert_eq!(
|
|
env.get_var(&Iden {
|
|
iden: "bar".to_owned(),
|
|
span: 1..1,
|
|
})
|
|
.unwrap(),
|
|
Value::Int(33)
|
|
);
|
|
|
|
// Assigning an existing variable.
|
|
eval(&mut env, "foo = \"hi\";").unwrap();
|
|
assert_eq!(
|
|
env.get_var(&Iden {
|
|
iden: "foo".to_owned(),
|
|
span: 1..1,
|
|
})
|
|
.unwrap(),
|
|
Value::Str("hi".to_owned())
|
|
);
|
|
|
|
// But variable assignment should be illegal when the variable
|
|
// hasn't been declared in advance.
|
|
eval(&mut env, "invalid = bar + 1;").unwrap_err();
|
|
}
|
|
|
|
#[test]
|
|
fn scope_visibility_rules() {
|
|
// Declaration and assignment of variables declared in an `if`
|
|
// statement should have no effect on those declared outside
|
|
// of it.
|
|
let mut env = ExecEnv::new();
|
|
eval(
|
|
&mut env,
|
|
"var foo = 1; foo = 2; if (true) { var foo = 3; foo = 4; }",
|
|
)
|
|
.unwrap();
|
|
|
|
assert_eq!(
|
|
env.get_var(&Iden {
|
|
iden: "foo".to_owned(),
|
|
span: 1..1,
|
|
})
|
|
.unwrap(),
|
|
Value::Int(2)
|
|
);
|
|
}
|
|
}
|