init: Add Token definition and Tokenizer logic.

.gitignore

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+/target
+
+
+# Added by cargo
+#
+# already existing elements were commented out
+
+#/target

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "bucky"
+version = "0.1.0"
+dependencies = [
+ "multipeek",
+ "unicode-xid",
+]
+
+[[package]]
+name = "multipeek"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1d6b1cf1c2ae7c8c3898cbf8354ee836bc7037e35592d3739a9901d53c97b6a2"
+
+[[package]]
+name = "unicode-xid"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ebc1c04c71510c7f702b52b7c350734c9ff1295c464a03335b00bb84fc54f853"

Cargo.toml

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+[package]
+name = "bucky"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+multipeek = "0.1.2"
+unicode-xid = "0.2.6"

example/main.bky

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+/// This function computes the n-th value of the fibbonacci sequence.
+fn fib(n: u64): u64 {
+    if n < 2 {
+        return n;
+    }
+
+    return fib(n - 1) + fib(n - 2);
+}

src/main.rs

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+use crate::token::Tokenizer;
+
+pub mod token;
+
+fn main() {
+    let input = include_str!("../example/main.bky");
+
+    for token in Tokenizer::new(input) {
+        println!("{token:?}");
+    }
+}

src/token.rs

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+use std::str::Chars;
+
+use multipeek::{IteratorExt, MultiPeek};
+use unicode_xid::UnicodeXID;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Span {
+    pub start: usize,
+    pub end: usize,
+}
+
+impl Span {
+    pub const fn new(start: usize, end: usize) -> Self {
+        Self { start, end }
+    }
+
+    pub const fn from_offset_and_length(start: usize, length: usize) -> Self {
+        Self {
+            start,
+            end: start + length,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Token<'src> {
+    pub kind: TokenKind,
+    pub span: Span,
+    pub text: &'src str,
+}
+
+impl<'src> Token<'src> {
+    pub const fn new(kind: TokenKind, span: Span, text: &'src str) -> Self {
+        Self { kind, span, text }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum TokenKind {
+    InvalidCharacter,
+
+    KwFn,
+    KwIf,
+    KwLet,
+    KwLoop,
+    KwWhile,
+    KwBreak,
+    KwReturn,
+
+    Identifier,
+    Integer,
+    Boolean,
+
+    Plus,
+    Minus,
+    Asterisk,
+    Slash,
+    Percent,
+    Ampersand,
+    Pipe,
+    Caret,
+    Bang,
+
+    Equal,
+    Unequal,
+    LessThan,
+    LessThanOrEqual,
+    GreaterThan,
+    GreaterThanOrEqual,
+
+    Assign,
+    Dot,
+    Comma,
+    Colon,
+    Semicolon,
+
+    LeftParen,
+    RightParen,
+    LeftBrace,
+    RightBrace,
+    LeftBracket,
+    RightBracket,
+}
+
+pub struct Tokenizer<'src> {
+    input: &'src str,
+    chars: MultiPeek<Chars<'src>>,
+    position: usize,
+}
+
+impl<'src> Tokenizer<'src> {
+    pub fn new(input: &'src str) -> Self {
+        Self {
+            input,
+            chars: input.chars().multipeek(),
+            position: 0,
+        }
+    }
+
+    fn span(&self, start: usize) -> Span {
+        Span::new(start, self.position)
+    }
+
+    fn text(&self, span: Span) -> &'src str {
+        &self.input[span.start..span.end]
+    }
+
+    fn peek(&mut self) -> Option<char> {
+        self.chars.peek().copied()
+    }
+
+    fn peek_nth(&mut self, n: usize) -> Option<char> {
+        self.chars.peek_nth(n).copied()
+    }
+
+    fn consume(&mut self) -> Option<char> {
+        let ch = self.chars.next()?;
+        self.position += 1;
+        Some(ch)
+    }
+
+    fn skip_whitespace(&mut self) {
+        while self.peek().is_some_and(char::is_whitespace) {
+            self.consume();
+        }
+    }
+
+    fn skip_line(&mut self) {
+        while self.peek().is_some_and(|ch| ch != '\n') {
+            self.consume();
+        }
+
+        self.consume();
+    }
+
+    fn skip_block_comment(&mut self) {
+        let mut indent = 1;
+
+        self.consume();
+        self.consume();
+
+        while indent > 0 {
+            let Some(peek_1st) = self.peek() else {
+                break;
+            };
+
+            let peek_2nd = self.peek_nth(1).unwrap_or('\0');
+
+            match (peek_1st, peek_2nd) {
+                ('/', '*') => {
+                    indent += 1;
+                    self.consume();
+                    self.consume();
+                }
+                ('*', '/') => {
+                    indent -= 1;
+                    self.consume();
+                    self.consume();
+                }
+                _ => {
+                    self.consume();
+                }
+            }
+        }
+    }
+
+    fn next_identifier(&mut self) -> Token<'src> {
+        let start = self.position;
+
+        self.consume();
+        while self.peek().is_some_and(|ch| ch.is_xid_continue()) {
+            self.consume();
+        }
+
+        let span = self.span(start);
+        let text = self.text(span);
+
+        let kind = match text {
+            "fn" => TokenKind::KwFn,
+            "if" => TokenKind::KwIf,
+            "let" => TokenKind::KwLet,
+            "loop" => TokenKind::KwLoop,
+            "while" => TokenKind::KwWhile,
+            "break" => TokenKind::KwBreak,
+            "return" => TokenKind::KwReturn,
+
+            _ => TokenKind::Identifier,
+        };
+
+        Token::new(kind, span, text)
+    }
+
+    fn next_integer(&mut self) -> Token<'src> {
+        let start = self.position;
+
+        self.consume();
+        while self.peek().is_some_and(|ch| ch.is_ascii_digit()) {
+            self.consume();
+        }
+
+        let span = self.span(start);
+        let text = self.text(span);
+
+        Token::new(TokenKind::Integer, span, text)
+    }
+
+    fn next_punctuation(&mut self) -> Token<'src> {
+        let start = self.position;
+
+        macro_rules! single {
+            ($kind:expr) => {{
+                self.consume();
+                $kind
+            }};
+        }
+
+        let kind = match self.peek().unwrap() {
+            '+' => single!(TokenKind::Plus),
+            '-' => single!(TokenKind::Minus),
+            '*' => single!(TokenKind::Asterisk),
+            '/' => single!(TokenKind::Slash),
+            '%' => single!(TokenKind::Percent),
+            '&' => single!(TokenKind::Ampersand),
+            '|' => single!(TokenKind::Pipe),
+            '^' => single!(TokenKind::Caret),
+
+            '.' => single!(TokenKind::Dot),
+            ',' => single!(TokenKind::Comma),
+            ':' => single!(TokenKind::Colon),
+            ';' => single!(TokenKind::Semicolon),
+
+            '=' => {
+                if self.peek() == Some('=') {
+                    self.consume();
+                    self.consume();
+                    TokenKind::Equal
+                } else {
+                    self.consume();
+                    TokenKind::Assign
+                }
+            }
+            '!' => {
+                if self.peek() == Some('=') {
+                    self.consume();
+                    self.consume();
+                    TokenKind::Unequal
+                } else {
+                    self.consume();
+                    TokenKind::Bang
+                }
+            }
+            '<' => {
+                if self.peek() == Some('=') {
+                    self.consume();
+                    self.consume();
+                    TokenKind::LessThanOrEqual
+                } else {
+                    self.consume();
+                    TokenKind::LessThan
+                }
+            }
+            '>' => {
+                if self.peek() == Some('=') {
+                    self.consume();
+                    self.consume();
+                    TokenKind::GreaterThanOrEqual
+                } else {
+                    self.consume();
+                    TokenKind::GreaterThan
+                }
+            }
+
+            '(' => single!(TokenKind::LeftParen),
+            ')' => single!(TokenKind::RightParen),
+            '{' => single!(TokenKind::LeftBrace),
+            '}' => single!(TokenKind::RightBrace),
+            '[' => single!(TokenKind::LeftBracket),
+            ']' => single!(TokenKind::RightBracket),
+
+            _ => single!(TokenKind::InvalidCharacter),
+        };
+
+        let span = self.span(start);
+        let text = self.text(span);
+
+        Token::new(kind, span, text)
+    }
+}
+
+impl<'src> Iterator for Tokenizer<'src> {
+    type Item = Token<'src>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            self.skip_whitespace();
+
+            if self.peek() == Some('/') && self.peek_nth(1) == Some('/') {
+                self.skip_line();
+                continue;
+            }
+
+            if self.peek() == Some('/') && self.peek_nth(1) == Some('*') {
+                self.skip_block_comment();
+                continue;
+            }
+
+            let ch = self.peek()?;
+
+            if ch.is_xid_start() || ch == '_' {
+                return Some(self.next_identifier());
+            }
+
+            if ch.is_ascii_digit() {
+                return Some(self.next_integer());
+            }
+
+            return Some(self.next_punctuation());
+        }
+    }
+}