interpreter: Prototype interpreter

TODO: Type-checking, floats, variables & scope
TODO Later: A bytecode interpreter

libconlang/examples/interpret.rs

@@ -0,0 +1,77 @@
+//! This example grabs input from stdin or a file, lexes it, parses it, and interprets it
+use conlang::{interpreter::Interpreter, lexer::Lexer, parser::Parser};
+use std::{
+    error::Error,
+    io::{stdin, stdout, IsTerminal, Write},
+    path::{Path, PathBuf},
+};
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let conf = Config::new();
+    if conf.paths.is_empty() {
+        take_stdin()?;
+    } else {
+        for path in conf.paths.iter().map(PathBuf::as_path) {
+            parse(&std::fs::read_to_string(path)?, Some(path))?;
+        }
+    }
+    Ok(())
+}
+
+struct Config {
+    paths: Vec<PathBuf>,
+}
+
+impl Config {
+    fn new() -> Self {
+        Config { paths: std::env::args().skip(1).map(PathBuf::from).collect() }
+    }
+}
+
+fn take_stdin() -> Result<(), Box<dyn Error>> {
+    const PROMPT: &str = "> ";
+    if stdin().is_terminal() {
+        print!("{PROMPT}");
+        stdout().flush()?;
+        for line in stdin().lines() {
+            let line = line?;
+            if !line.is_empty() {
+                let _ = run(&line).map_err(|e| eprintln!("{e}"));
+                println!();
+            }
+            print!("{PROMPT}");
+            stdout().flush()?;
+        }
+    } else {
+        parse(&std::io::read_to_string(stdin())?, None)?
+    }
+    Ok(())
+}
+
+fn parse(file: &str, path: Option<&Path>) -> Result<(), Box<dyn Error>> {
+    match Parser::from(Lexer::new(file)).parse() {
+        Ok(ast) => Interpreter::new().interpret(&ast)?,
+        Err(e) if e.start().is_some() => print!("{:?}:{}", path.unwrap_or(Path::new("-")), e),
+        Err(e) => print!("{e}"),
+    }
+    println!();
+    Ok(())
+}
+
+fn run(file: &str) -> Result<(), Box<dyn Error>> {
+    let mut interpreter = Interpreter::new();
+    // If it parses successfully as a program, run the program
+    match Parser::from(Lexer::new(file)).parse() {
+        Ok(ast) => interpreter.interpret(&ast)?,
+        Err(e) => {
+            // If not, re-parse as an expression, and print the stack
+            let Ok(expr) = Parser::from(Lexer::new(file)).parse_expr() else {
+                Err(e)?
+            };
+            for value in interpreter.eval(&expr)? {
+                println!("{value}");
+            }
+        }
+    }
+    Ok(())
+}

libconlang/src/interpreter.rs

@@ -0,0 +1,504 @@
+//! Interprets an AST as a program
+
+use crate::ast::preamble::*;
+use error::{Error, IResult, Reason};
+use temp_type_impl::ConValue;
+
+pub mod temp_type_impl {
+    //! Temporary implementations of Conlang values until I'm able to
+    use super::error::{Error, IResult, Reason};
+    use std::ops::*;
+    /// A Conlang value
+    ///
+    /// This is a hack to work around the fact that Conlang doesn't have a functioning type system
+    /// yet :(
+    #[derive(Clone, Debug)]
+    pub enum ConValue {
+        /// The empty/unit `()` type
+        Empty,
+        /// An integer
+        Int(i128),
+        /// A boolean
+        Bool(bool),
+        /// A unicode character
+        Char(char),
+        /// A string
+        String(String),
+    }
+    impl ConValue {
+        /// Gets whether the current value is true or false
+        pub fn truthy(&self) -> IResult<bool> {
+            match self {
+                ConValue::Bool(v) => Ok(*v),
+                _ => Err(Error::with_reason(Reason::TypeError))?,
+            }
+        }
+        cmp! {
+            lt: false, <;
+            lt_eq: true, <=;
+            eq: true, ==;
+            neq: false, !=;
+            gt_eq: true, >=;
+            gt: false, >;
+        }
+    }
+    /// Templates comparison functions for [ConValue]
+    macro cmp ($($fn:ident: $empty:literal, $op:tt);*$(;)?) {$(
+        /// TODO: Remove when functions are implemented:
+        ///       Desugar into function calls
+        pub fn $fn(&self, other: &Self) -> IResult<Self> {
+            match (self, other) {
+                (Self::Empty, Self::Empty) => Ok(Self::Bool($empty)),
+                (Self::Int(a), Self::Int(b)) => Ok(Self::Bool(a $op b)),
+                (Self::Bool(a), Self::Bool(b)) => Ok(Self::Bool(a $op b)),
+                (Self::Char(a), Self::Char(b)) => Ok(Self::Bool(a $op b)),
+                (Self::String(a), Self::String(b)) => Ok(Self::Bool(a $op b)),
+                _ => Err(Error::with_reason(Reason::TypeError))
+            }
+        }
+    )*}
+    /// Implements [From] for an enum with 1-tuple variants
+    macro from ($($T:ty => $v:expr),*$(,)?) {
+        $(impl From<$T> for ConValue {
+            fn from(value: $T) -> Self { $v(value.into()) }
+        })*
+    }
+    from! {
+        i128 => ConValue::Int,
+        bool => ConValue::Bool,
+        char => ConValue::Char,
+        &str => ConValue::String,
+        String => ConValue::String,
+    }
+    impl From<()> for ConValue {
+        fn from(_: ()) -> Self {
+            Self::Empty
+        }
+    }
+
+    /// Implements binary [std::ops] traits for [ConValue]
+    ///
+    /// TODO: Desugar operators into function calls
+    macro ops($($trait:ty: $fn:ident = [$($match:tt)*])*) {
+        $(impl $trait for ConValue {
+            type Output = IResult<Self>;
+            /// TODO: Desugar operators into function calls
+            fn $fn(self, rhs: Self) -> Self::Output {Ok(match (self, rhs) {$($match)*})}
+        })*
+    }
+    ops! {
+        Add: add = [
+            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
+            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a + b),
+            (ConValue::String(a), ConValue::String(b)) => ConValue::String(a + &b),
+            _ => Err(Error::with_reason(Reason::TypeError))?
+            ]
+        BitAnd: bitand = [
+            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
+            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a & b),
+            (ConValue::Bool(a), ConValue::Bool(b)) => ConValue::Bool(a & b),
+            _ => Err(Error::with_reason(Reason::TypeError))?
+        ]
+        BitOr: bitor = [
+            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
+            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a | b),
+            (ConValue::Bool(a), ConValue::Bool(b)) => ConValue::Bool(a | b),
+            _ => Err(Error::with_reason(Reason::TypeError))?
+        ]
+        BitXor: bitxor = [
+            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
+            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a ^ b),
+            (ConValue::Bool(a), ConValue::Bool(b)) => ConValue::Bool(a ^ b),
+            _ => Err(Error::with_reason(Reason::TypeError))?
+        ]
+        Div: div = [
+            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
+            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a / b),
+            _ => Err(Error::with_reason(Reason::TypeError))?
+        ]
+        Mul: mul = [
+            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
+            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a * b),
+            _ => Err(Error::with_reason(Reason::TypeError))?
+        ]
+        Rem: rem = [
+            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
+            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a % b),
+            _ => Err(Error::with_reason(Reason::TypeError))?
+        ]
+        Shl: shl = [
+            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
+            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a << b),
+            _ => Err(Error::with_reason(Reason::TypeError))?
+        ]
+        Shr: shr = [
+            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
+            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a >> b),
+            _ => Err(Error::with_reason(Reason::TypeError))?
+        ]
+        Sub: sub = [
+            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
+            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a - b),
+            _ => Err(Error::with_reason(Reason::TypeError))?
+        ]
+    }
+    impl Neg for ConValue {
+        type Output = IResult<Self>;
+        fn neg(self) -> Self::Output {
+            Ok(match self {
+                ConValue::Empty => ConValue::Empty,
+                ConValue::Int(v) => ConValue::Int(-v),
+                _ => Err(Error::with_reason(Reason::TypeError))?,
+            })
+        }
+    }
+    impl Not for ConValue {
+        type Output = IResult<Self>;
+        fn not(self) -> Self::Output {
+            Ok(match self {
+                ConValue::Empty => ConValue::Empty,
+                ConValue::Int(v) => ConValue::Int(!v),
+                ConValue::Bool(v) => ConValue::Bool(!v),
+                _ => Err(Error::with_reason(Reason::TypeError))?,
+            })
+        }
+    }
+    impl std::fmt::Display for ConValue {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            match self {
+                ConValue::Empty => "Empty".fmt(f),
+                ConValue::Int(v) => v.fmt(f),
+                ConValue::Bool(v) => v.fmt(f),
+                ConValue::Char(v) => write!(f, "'{v}'"),
+                ConValue::String(v) => write!(f, "\"{v}\""),
+            }
+        }
+    }
+}
+
+/// A work-in-progress tree walk interpreter for Conlang
+#[derive(Clone, Debug, Default)]
+pub struct Interpreter {
+    stack: Vec<ConValue>,
+}
+
+impl Interpreter {
+    /// Creates a new [Interpreter]
+    pub fn new() -> Self {
+        Default::default()
+    }
+    /// Interprets the [Start] of a syntax tree
+    pub fn interpret(&mut self, start: &Start) -> IResult<()> {
+        self.visit(start)
+    }
+    /// Evaluates a single [Expression](expression::Expr)
+    pub fn eval(mut self, expr: &expression::Expr) -> IResult<Vec<ConValue>> {
+        self.visit_expr(expr)?;
+        Ok(self.stack)
+    }
+    fn push(&mut self, value: impl Into<ConValue>) {
+        self.stack.push(value.into())
+    }
+    fn peek(&mut self) -> IResult<&ConValue> {
+        self.stack
+            .last()
+            .ok_or(Error::with_reason(Reason::StackUnderflow))
+    }
+    fn pop(&mut self) -> IResult<ConValue> {
+        self.stack
+            .pop()
+            .ok_or(Error::with_reason(Reason::StackUnderflow))
+    }
+    fn pop_two(&mut self) -> IResult<(ConValue, ConValue)> {
+        Ok((self.pop()?, self.pop()?))
+    }
+}
+
+impl Visitor<IResult<()>> for Interpreter {
+    fn visit_program(&mut self, prog: &Program) -> IResult<()> {
+        for stmt in &prog.0 {
+            self.visit_statement(stmt)?;
+        }
+        Ok(())
+    }
+
+    fn visit_statement(&mut self, stmt: &Stmt) -> IResult<()> {
+        match stmt {
+            Stmt::Let { name, mutable, ty, init } => todo!(
+                "let{} {name:?}: {ty:?} = {init:?}",
+                if *mutable { " mut" } else { "" }
+            ),
+            Stmt::Expr(e) => {
+                self.visit_expr(e)?;
+                self.pop().map(drop)
+            }
+        }
+    }
+
+    fn visit_operation(&mut self, expr: &math::Operation) -> IResult<()> {
+        use math::Operation;
+        // TODO: the indentation depth here is driving me insane.
+        //       maybe refactor the ast to break binary and unary
+        //       operations into their own nodes, and use
+        //       Operation to unify them?
+        match expr {
+            Operation::Binary { first, other } => {
+                self.visit_operation(first)?;
+                for (op, other) in other {
+                    match op {
+                        operator::Binary::LogAnd => {
+                            if self.peek()?.truthy()? {
+                                self.pop()?;
+                                self.visit_operation(other)?;
+                            }
+                        }
+                        operator::Binary::LogOr => {
+                            if !self.peek()?.truthy()? {
+                                self.pop()?;
+                                self.visit_operation(other)?;
+                            }
+                        }
+                        operator::Binary::LogXor => {
+                            let first = self.pop()?.truthy()?;
+                            self.visit_operation(other)?;
+                            let second = self.pop()?.truthy()?;
+                            self.push(first ^ second);
+                        }
+                        _ => {
+                            self.visit_operation(other)?;
+                            self.visit_binary_op(op)?;
+                        }
+                    }
+                }
+                Ok(())
+            }
+            Operation::Unary { operators, operand } => {
+                self.visit_primary(operand)?;
+                for op in operators.iter().rev() {
+                    self.visit_unary_op(op)?;
+                }
+                Ok(())
+            }
+        }
+    }
+
+    fn visit_binary_op(&mut self, op: &operator::Binary) -> IResult<()> {
+        use operator::Binary;
+        let (second, first) = self.pop_two()?;
+        self.push(match op {
+            Binary::Mul => first * second,
+            Binary::Div => first / second,
+            Binary::Rem => first % second,
+            Binary::Add => first + second,
+            Binary::Sub => first - second,
+            Binary::Lsh => first << second,
+            Binary::Rsh => first >> second,
+            Binary::BitAnd => first & second,
+            Binary::BitOr => first | second,
+            Binary::BitXor => first ^ second,
+            Binary::LogAnd | Binary::LogOr | Binary::LogXor => {
+                unimplemented!("Implemented in visit_operation")
+            }
+            Binary::RangeExc => todo!("Range expressions"),
+            Binary::RangeInc => todo!("Range expressions"),
+            Binary::Less => first.lt(&second),
+            Binary::LessEq => first.lt_eq(&second),
+            Binary::Equal => first.eq(&second),
+            Binary::NotEq => first.neq(&second),
+            Binary::GreaterEq => first.gt_eq(&second),
+            Binary::Greater => first.gt(&second),
+            Binary::Assign => todo!("Assignment"),
+            Binary::AddAssign => todo!("Assignment"),
+            Binary::SubAssign => todo!("Assignment"),
+            Binary::MulAssign => todo!("Assignment"),
+            Binary::DivAssign => todo!("Assignment"),
+            Binary::RemAssign => todo!("Assignment"),
+            Binary::BitAndAssign => todo!("Assignment"),
+            Binary::BitOrAssign => todo!("Assignment"),
+            Binary::BitXorAssign => todo!("Assignment"),
+            Binary::ShlAssign => todo!("Assignment"),
+            Binary::ShrAssign => todo!("Assignment"),
+        }?);
+        Ok(())
+    }
+
+    fn visit_unary_op(&mut self, op: &operator::Unary) -> IResult<()> {
+        let operand = self.pop()?;
+        self.push(match op {
+            operator::Unary::RefRef => todo!(),
+            operator::Unary::Ref => todo!(),
+            operator::Unary::Deref => todo!(),
+            operator::Unary::Neg => (-operand)?,
+            operator::Unary::Not => (!operand)?,
+            operator::Unary::At => todo!(),
+            operator::Unary::Hash => {
+                println!("{operand}");
+                operand
+            }
+            operator::Unary::Tilde => todo!(),
+        });
+        Ok(())
+    }
+
+    fn visit_if(&mut self, expr: &control::If) -> IResult<()> {
+        self.visit_expr(&expr.cond)?;
+        if self.pop()?.truthy()? {
+            self.visit_block(&expr.body)?;
+        } else if let Some(block) = &expr.else_ {
+            self.visit_else(block)?;
+        }
+        Ok(())
+    }
+
+    fn visit_while(&mut self, expr: &control::While) -> IResult<()> {
+        let mut broke = false;
+        while {
+            self.visit_expr(&expr.cond)?;
+            self.pop()?.truthy()?
+        } {
+            let Err(out) = self.visit_block(&expr.body) else {
+                continue;
+            };
+            match out.reason() {
+                Reason::Continue => continue,
+                Reason::Break(value) => {
+                    self.push(value);
+                    broke = true;
+                    break;
+                }
+                r => Err(Error::with_reason(r))?,
+            }
+        }
+        if let (Some(r#else), false) = (&expr.else_, broke) {
+            self.visit_else(r#else)?;
+        }
+        Ok(())
+    }
+
+    fn visit_for(&mut self, expr: &control::For) -> IResult<()> {
+        todo!("Visit for: {expr:?}")
+    }
+
+    fn visit_else(&mut self, else_: &control::Else) -> IResult<()> {
+        self.visit_block(&else_.block)
+    }
+
+    fn visit_continue(&mut self, _: &control::Continue) -> IResult<()> {
+        Err(Error::cnt())
+    }
+
+    fn visit_break(&mut self, brk: &control::Break) -> IResult<()> {
+        Err(Error::brk({
+            self.visit_expr(&brk.expr)?;
+            self.pop()?
+        }))
+    }
+
+    fn visit_return(&mut self, ret: &control::Return) -> IResult<()> {
+        Err(Error::ret({
+            self.visit_expr(&ret.expr)?;
+            self.pop()?
+        }))
+    }
+
+    fn visit_identifier(&mut self, ident: &Identifier) -> IResult<()> {
+        todo!("Identifier lookup and scoping rules: {ident:?}")
+    }
+
+    fn visit_string_literal(&mut self, string: &str) -> IResult<()> {
+        self.push(string);
+        Ok(())
+    }
+
+    fn visit_char_literal(&mut self, char: &char) -> IResult<()> {
+        self.push(*char);
+        Ok(())
+    }
+
+    fn visit_bool_literal(&mut self, bool: &bool) -> IResult<()> {
+        self.push(*bool);
+        Ok(())
+    }
+
+    fn visit_float_literal(&mut self, float: &literal::Float) -> IResult<()> {
+        todo!("visit floats in interpreter: {float:?}")
+    }
+
+    fn visit_int_literal(&mut self, int: &u128) -> IResult<()> {
+        self.push((*int) as i128);
+        Ok(())
+    }
+
+    fn visit_empty(&mut self) -> IResult<()> {
+        self.push(());
+        Ok(())
+    }
+}
+
+pub mod error {
+    //! The [Error] type represents any error thrown by the [Interpreter](super::Interpreter)
+    use super::temp_type_impl::ConValue;
+
+    pub type IResult<T> = Result<T, Error>;
+    /// Represents any error thrown by the [Interpreter](super::Interpreter)
+    #[derive(Clone, Debug)]
+    pub struct Error {
+        reason: Reason,
+    }
+    impl Error {
+        /// Returns the [Reason] for this error
+        pub fn reason(self) -> Reason {
+            self.reason
+        }
+        /// Creates an error with a given [Reason]
+        pub(crate) fn with_reason(reason: Reason) -> Self {
+            Self { reason }
+        }
+        /// Creates a [Return](Reason::Return) error, with the given [value](ConValue)
+        pub fn ret(value: ConValue) -> Self {
+            Self { reason: Reason::Return(value) }
+        }
+        /// Creates a [Break](Reason::Break) error, with the given [value](ConValue)
+        pub fn brk(value: ConValue) -> Self {
+            Self { reason: Reason::Break(value) }
+        }
+        /// Creates a [Continue](Reason::Continue) error
+        pub fn cnt() -> Self {
+            Self { reason: Reason::Continue }
+        }
+    }
+
+    /// The reason for the [Error]
+    #[derive(Clone, Debug)]
+    pub enum Reason {
+        /// Propagate a Return value
+        Return(ConValue),
+        /// Propagate a Break value
+        Break(ConValue),
+        /// Continue to the next iteration of a loop
+        Continue,
+        /// Underflowed the stack
+        StackUnderflow,
+        /// Type incompatibility
+        // TODO: store the type information in this error
+        TypeError,
+    }
+
+    impl std::error::Error for Error {}
+    impl std::fmt::Display for Error {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            self.reason.fmt(f)
+        }
+    }
+    impl std::fmt::Display for Reason {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            match self {
+                Reason::Return(value) => write!(f, "return {value:?}"),
+                Reason::Break(value) => write!(f, "break {value:?}"),
+                Reason::Continue => "continue".fmt(f),
+                Reason::StackUnderflow => "Stack underflow".fmt(f),
+                Reason::TypeError => "Type error".fmt(f),
+            }
+        }
+    }
+}

libconlang/src/lib.rs

@@ -1,4 +1,4 @@
-//! Conlang is an expression-based programming language with similarities to Rust
+//! Conlang is an expression-based programming language with similarities to Rust and Python
 #![warn(clippy::all)]
 #![feature(decl_macro)]
 
@@ -12,9 +12,7 @@ pub mod parser;
 
 pub mod pretty_printer;
 
-pub mod interpreter {
-    //! Interprets an AST as a program
-}
+pub mod interpreter;
 
 #[cfg(test)]
 mod tests;

libconlang/src/parser.rs

@@ -69,7 +69,7 @@ pub mod error {
         reason: Reason,
         start: Option<Token>,
     }
-
+    impl std::error::Error for Error {}
     impl Display for Error {
         fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
             if let Some(token) = &self.start {