feat: Add Expression definition and parsing logic.

src/ast.rs

@@ -0,0 +1,60 @@
+use crate::token::Span;
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct Expression {
+    pub kind: ExpressionKind,
+    pub span: Span,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum ExpressionKind {
+    Integer(u64),
+    Boolean(bool),
+    Identifier(Box<str>),
+
+    Unary {
+        op: UnaryOp,
+        op_span: Span,
+        expr: Box<Expression>,
+    },
+
+    Binary {
+        op: BinaryOp,
+        op_span: Span,
+        left: Box<Expression>,
+        right: Box<Expression>,
+    },
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum UnaryOp {
+    LogicalNot,
+    BitwiseNot,
+    Negate,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BinaryOp {
+    Add,
+    Subtract,
+    Multiply,
+    Divide,
+    Remainder,
+
+    BitwiseAnd,
+    BitwiseOr,
+    BitwiseXor,
+
+    LogicalAnd,
+    LogicalOr,
+
+    Equal,
+    Unequal,
+    LessThan,
+    LessThanOrEqual,
+    GreaterThan,
+    GreaterThanOrEqual,
+
+    Assign,
+    Member,
+}

src/main.rs

@@ -1,11 +1,11 @@
-use crate::token::Tokenizer;
+use crate::parser::Parser;
 
+pub mod ast;
+pub mod parser;
 pub mod token;
 
 fn main() {
-    let input = include_str!("../example/main.bky");
+    let mut parser = Parser::new("user.age >= 18");
 
-    for token in Tokenizer::new(input) {
-        println!("{token:?}");
-    }
+    println!("{:#?}", parser.parse_expression(0));
 }

src/parser.rs

@@ -0,0 +1,185 @@
+use multipeek::{IteratorExt, MultiPeek};
+
+use crate::{
+    ast::*,
+    token::{Span, Token, TokenKind, Tokenizer},
+};
+
+#[derive(Debug)]
+pub enum ParserError {
+    UnexpectedToken {
+        expected: &'static [TokenKind],
+        found: TokenKind,
+        span: Span,
+    },
+    UnexpectedEof,
+}
+
+pub type ParserResult<T> = std::result::Result<T, ParserError>;
+
+pub struct Parser<'src> {
+    tokens: MultiPeek<Tokenizer<'src>>,
+}
+
+impl<'src> Parser<'src> {
+    pub fn new(input: &'src str) -> Self {
+        Self {
+            tokens: Tokenizer::new(input).multipeek(),
+        }
+    }
+
+    fn peek(&mut self) -> Option<Token<'src>> {
+        self.tokens.peek().copied()
+    }
+
+    fn peek_no_eof(&mut self) -> ParserResult<Token<'src>> {
+        self.peek().ok_or(ParserError::UnexpectedEof)
+    }
+
+    fn consume(&mut self) -> Option<Token<'src>> {
+        self.tokens.next()
+    }
+
+    pub fn parse_expression(&mut self, min_binding_power: u8) -> ParserResult<Expression> {
+        let mut left = self.parse_leading_expression()?;
+
+        loop {
+            let Some(peek) = self.peek() else {
+                break;
+            };
+
+            if let Some((left_binding_power, right_binding_power, op)) =
+                infix_binding_power(peek.kind)
+            {
+                if left_binding_power < min_binding_power {
+                    break;
+                }
+
+                // consume operator token
+                self.consume();
+
+                let right = self.parse_expression(right_binding_power)?;
+                let span = Span::new(left.span.start, right.span.end);
+
+                left = Expression {
+                    kind: ExpressionKind::Binary {
+                        op,
+                        op_span: peek.span,
+                        left: Box::new(left),
+                        right: Box::new(right),
+                    },
+                    span,
+                };
+            }
+        }
+
+        Ok(left)
+    }
+
+    fn parse_leading_expression(&mut self) -> ParserResult<Expression> {
+        let peek = self.peek_no_eof()?;
+
+        match peek.kind {
+            TokenKind::Identifier => {
+                self.consume();
+
+                let text = peek.text.to_string().into_boxed_str();
+                Ok(Expression {
+                    kind: ExpressionKind::Identifier(text),
+                    span: peek.span,
+                })
+            }
+            TokenKind::Integer => {
+                self.consume();
+
+                let value = peek.text.parse::<u64>().unwrap();
+                Ok(Expression {
+                    kind: ExpressionKind::Integer(value),
+                    span: peek.span,
+                })
+            }
+            TokenKind::Boolean => {
+                self.consume();
+
+                let value = peek.text == "true";
+                Ok(Expression {
+                    kind: ExpressionKind::Boolean(value),
+                    span: peek.span,
+                })
+            }
+            _ => {
+                if let Some((right_binding_power, op)) = prefix_binding_power(peek.kind) {
+                    self.consume();
+
+                    let op_span = peek.span;
+                    let expr = self.parse_expression(right_binding_power)?;
+
+                    Ok(Expression {
+                        kind: ExpressionKind::Unary {
+                            op,
+                            op_span,
+                            expr: Box::new(expr),
+                        },
+                        span: peek.span,
+                    })
+                } else {
+                    Err(ParserError::UnexpectedToken {
+                        expected: &[
+                            TokenKind::Identifier,
+                            TokenKind::Integer,
+                            TokenKind::Boolean,
+                            TokenKind::KwNot,
+                            TokenKind::Tilde,
+                            TokenKind::Minus,
+                        ],
+                        found: peek.kind,
+                        span: peek.span,
+                    })
+                }
+            }
+        }
+    }
+}
+
+fn prefix_binding_power(kind: TokenKind) -> Option<(u8, UnaryOp)> {
+    // Update `parse_leading_expression` when adding more operators.
+    Some(match kind {
+        TokenKind::KwNot => (28, UnaryOp::LogicalNot),
+        TokenKind::Tilde => (28, UnaryOp::BitwiseNot),
+        TokenKind::Minus => (28, UnaryOp::Negate),
+
+        _ => return None,
+    })
+}
+
+fn infix_binding_power(kind: TokenKind) -> Option<(u8, u8, BinaryOp)> {
+    Some(match kind {
+        TokenKind::Dot => (30, 31, BinaryOp::Member),
+
+        TokenKind::Asterisk => (26, 27, BinaryOp::Multiply),
+        TokenKind::Slash => (26, 27, BinaryOp::Divide),
+        TokenKind::Percent => (26, 27, BinaryOp::Remainder),
+
+        TokenKind::Plus => (24, 25, BinaryOp::Add),
+        TokenKind::Minus => (24, 25, BinaryOp::Subtract),
+
+        TokenKind::LessThan => (20, 21, BinaryOp::LessThan),
+        TokenKind::LessThanOrEqual => (20, 21, BinaryOp::LessThanOrEqual),
+        TokenKind::GreaterThan => (20, 21, BinaryOp::GreaterThan),
+        TokenKind::GreaterThanOrEqual => (20, 21, BinaryOp::GreaterThanOrEqual),
+
+        TokenKind::Equal => (18, 19, BinaryOp::Equal),
+        TokenKind::Unequal => (18, 19, BinaryOp::Unequal),
+
+        TokenKind::Ampersand => (16, 17, BinaryOp::BitwiseAnd),
+        TokenKind::Caret => (14, 15, BinaryOp::BitwiseXor),
+        TokenKind::Pipe => (12, 13, BinaryOp::BitwiseOr),
+
+        TokenKind::KwAnd => (10, 11, BinaryOp::LogicalAnd),
+        TokenKind::KwOr => (8, 9, BinaryOp::LogicalOr),
+
+        TokenKind::Assign => (5, 4, BinaryOp::Assign),
+
+        _ => return None,
+    })
+}

src/token.rs

@@ -47,6 +47,10 @@ pub enum TokenKind {
     KwBreak,
     KwReturn,
 
+    KwNot,
+    KwAnd,
+    KwOr,
+
     Identifier,
     Integer,
     Boolean,
@@ -59,7 +63,7 @@ pub enum TokenKind {
     Ampersand,
     Pipe,
     Caret,
-    Bang,
+    Tilde,
 
     Equal,
     Unequal,
@@ -184,6 +188,10 @@ impl<'src> Tokenizer<'src> {
             "break" => TokenKind::KwBreak,
             "return" => TokenKind::KwReturn,
 
+            "or" => TokenKind::KwOr,
+            "and" => TokenKind::KwAnd,
+            "not" => TokenKind::KwNot,
+
             _ => TokenKind::Identifier,
         };
 
@@ -223,6 +231,7 @@ impl<'src> Tokenizer<'src> {
             '&' => single!(TokenKind::Ampersand),
             '|' => single!(TokenKind::Pipe),
             '^' => single!(TokenKind::Caret),
+            '~' => single!(TokenKind::Tilde),
 
             '.' => single!(TokenKind::Dot),
             ',' => single!(TokenKind::Comma),
@@ -230,42 +239,42 @@ impl<'src> Tokenizer<'src> {
             ';' => single!(TokenKind::Semicolon),
 
             '=' => {
+                self.consume();
+
                 if self.peek() == Some('=') {
-                    self.consume();
                     self.consume();
                     TokenKind::Equal
                 } else {
-                    self.consume();
                     TokenKind::Assign
                 }
             }
             '!' => {
+                self.consume();
+
                 if self.peek() == Some('=') {
-                    self.consume();
                     self.consume();
                     TokenKind::Unequal
                 } else {
-                    self.consume();
-                    TokenKind::Bang
+                    TokenKind::InvalidCharacter
                 }
             }
             '<' => {
+                self.consume();
+
                 if self.peek() == Some('=') {
-                    self.consume();
                     self.consume();
                     TokenKind::LessThanOrEqual
                 } else {
-                    self.consume();
                     TokenKind::LessThan
                 }
             }
             '>' => {
+                self.consume();
+
                 if self.peek() == Some('=') {
-                    self.consume();
                     self.consume();
                     TokenKind::GreaterThanOrEqual
                 } else {
-                    self.consume();
                     TokenKind::GreaterThan
                 }
             }