add lexer

src/main.rs

@@ -1,23 +1,59 @@
+#![allow(dead_code)]
+
+use std::str::Chars;
+
+#[derive(Debug)]
 enum TokenType {
     InvalidChar,
     MalformedString,
     MalformedComment,
+    Id,
     Int,
+    Decimal,
+    String,
+    False,
+    True,
+    If,
+    Else,
+    While,
+    For,
+    In,
+    Break,
+    Continue,
+    Function,
+    Return,
+    End,
+    Underscore,
     Plus,
     Minus,
     Asterisk,
     Slash,
     Percent,
+    PlusEqual,
+    MinusEqual,
+    AsteriskEqual,
+    SlashEqual,
+    PercentEqual,
     LParen,
     RParen,
+    LBrace,
+    RBrace,
+    LBracket,
+    RBracket,
+    Dot,
+    Comma,
+    Colon,
+    Semicolon,
 }
 
+#[derive(Debug)]
 struct Position {
     index: usize,
     line: i32,
     col: i32,
 }
 
+#[derive(Debug)]
 struct Token {
     token_type: TokenType,
     pos: Position,
@@ -26,12 +62,226 @@ struct Token {
 
 struct Lexer<'a> {
     text: &'a str,
-    i: i32,
+    chars: Chars<'a>,
+    current_char: Option<char>,
+    index: usize,
+    line: i32,
+    col: i32,
 }
 
 impl<'a> Lexer<'a> {
     pub fn new(text: &'a str) -> Self {
-        Self { text, i: 0 }
+        let mut chars = text.chars();
+        let first_char = chars.next();
+        Self {
+            text,
+            chars,
+            current_char: first_char,
+            index: 0,
+            line: 1,
+            col: 1,
+        }
+    }
+
+    fn next_token(&mut self) -> Option<Token> {
+        if self.done() {
+            return None;
+        }
+        match self.current() {
+            ' ' | '\t' | '\r' | '\n' => self.skip_whitespace(),
+            '1'..='9' => Some(self.int_token()),
+            'a'..='z' | 'A'..='Z' | '_' => Some(self.id_token()),
+            '"' => Some(self.string_token()),
+            '+' => {
+                Some(self.single_or_double_char_token(TokenType::Plus, '=', TokenType::PlusEqual))
+            }
+            '-' => {
+                Some(self.single_or_double_char_token(TokenType::Minus, '=', TokenType::MinusEqual))
+            }
+            '*' => Some(self.single_or_double_char_token(
+                TokenType::Asterisk,
+                '=',
+                TokenType::AsteriskEqual,
+            )),
+            '/' => self.slash_token(),
+            '%' => Some(self.single_or_double_char_token(
+                TokenType::Percent,
+                '=',
+                TokenType::PercentEqual,
+            )),
+            '(' => Some(self.step_and_token(TokenType::LParen, self.pos())),
+            ')' => Some(self.step_and_token(TokenType::LParen, self.pos())),
+            '.' => Some(self.dot_token()),
+            _ => Some(self.step_and_token(TokenType::InvalidChar, self.pos())),
+        }
+    }
+
+    fn skip_whitespace(&mut self) -> Option<Token> {
+        while !self.done() && matches!(self.current(), ' ' | '\t' | '\r' | '\n') {
+            self.step()
+        }
+        self.next_token()
+    }
+
+    fn int_token(&mut self) -> Token {
+        let start = self.pos();
+        self.step();
+        while !self.done() && matches!(self.current(), '0'..='9') {
+            self.step();
+        }
+        self.token(TokenType::Int, start)
+    }
+
+    fn string_token(&mut self) -> Token {
+        let start = self.pos();
+        self.step();
+        let mut escaped = false;
+        while !self.done() && (self.current() != '"' || escaped) {
+            escaped = self.current() == '\\' && !escaped;
+            self.step();
+        }
+        if self.done() || self.current() != '"' {
+            self.step_and_token(TokenType::MalformedString, start)
+        } else {
+            self.step_and_token(TokenType::String, start)
+        }
+    }
+
+    fn id_token(&mut self) -> Token {
+        let start = self.pos();
+        self.step();
+        while !self.done() && matches!(self.current(), 'a'..='z' | 'A'..='Z' | '0'..='9' | '_') {
+            self.step();
+        }
+        match &self.text[start.index..self.index] {
+            "false" => self.token(TokenType::False, start),
+            "true" => self.token(TokenType::True, start),
+            "if" => self.token(TokenType::True, start),
+            "else" => self.token(TokenType::True, start),
+            "while" => self.token(TokenType::True, start),
+            "for" => self.token(TokenType::True, start),
+            "in" => self.token(TokenType::True, start),
+            "break" => self.token(TokenType::True, start),
+            "continue" => self.token(TokenType::True, start),
+            "function" => self.token(TokenType::True, start),
+            "return" => self.token(TokenType::True, start),
+            "end" => self.token(TokenType::True, start),
+            "underscore" => self.token(TokenType::True, start),
+            _ => self.token(TokenType::Id, start),
+        }
+    }
+
+    fn single_or_double_char_token(
+        &mut self,
+        single_type: TokenType,
+        double_char: char,
+        double_type: TokenType,
+    ) -> Token {
+        let start = self.pos();
+        self.step();
+        if !self.done() && self.current() == double_char {
+            self.step_and_token(double_type, start)
+        } else {
+            self.token(single_type, start)
+        }
+    }
+
+    fn slash_token(&mut self) -> Option<Token> {
+        let start = self.pos();
+        self.step();
+        if !self.done() && self.current() == '/' {
+            self.step();
+            while !self.done() && self.current() != '\n' {
+                self.step();
+            }
+            self.next_token()
+        } else if !self.done() && self.current() == '*' {
+            self.step();
+            let mut depth = 1;
+            let mut last_char: Option<char> = None;
+            while !self.done() {
+                match (last_char, self.current()) {
+                    (Some('/'), '*') => {
+                        depth += 1;
+                    }
+                    (Some('*'), '/') => {
+                        depth -= 1;
+                        if depth == 0 {
+                            self.step();
+                            break;
+                        }
+                    }
+                    _ => {}
+                }
+                last_char = Some(self.current());
+                self.step();
+            }
+            if depth != 0 {
+                Some(self.token(TokenType::MalformedComment, start))
+            } else {
+                self.next_token()
+            }
+        } else if !self.done() && self.current() == '=' {
+            return Some(self.step_and_token(TokenType::SlashEqual, start));
+        } else {
+            return Some(self.token(TokenType::Slash, start));
+        }
+    }
+
+    fn dot_token(&mut self) -> Token {
+        let start = self.pos();
+        self.step();
+        if !self.done() && matches!(self.current(), '0'..='9') {
+            self.step();
+            while !self.done() && matches!(self.current(), '0'..='9') {
+                self.step();
+            }
+            self.token(TokenType::Decimal, start)
+        } else {
+            self.token(TokenType::Dot, start)
+        }
+    }
+
+    fn step_and_token(&mut self, token_type: TokenType, start: Position) -> Token {
+        self.step();
+        self.token(token_type, start)
+    }
+
+    fn token(&self, token_type: TokenType, start: Position) -> Token {
+        Token {
+            token_type,
+            length: self.index - start.index,
+            pos: start,
+        }
+    }
+
+    fn pos(&self) -> Position {
+        Position {
+            index: self.index,
+            line: self.line,
+            col: self.col,
+        }
+    }
+
+    fn done(&self) -> bool {
+        self.current_char.is_none()
+    }
+
+    fn current(&self) -> char {
+        self.current_char.expect("done() not checked")
+    }
+
+    fn step(&mut self) {
+        self.index += 1;
+        if !self.done() {
+            if self.current() == '\n' {
+                self.line += 1;
+                self.col = 1;
+            } else {
+                self.col += 1;
+            }
+        }
+        self.current_char = self.chars.next();
     }
 }
 
@@ -39,10 +289,21 @@ impl<'a> Iterator for Lexer<'a> {
     type Item = Token;
 
     fn next(&mut self) -> Option<Self::Item> {
-        todo!()
+        self.next_token()
     }
 }
 
-fn main() {
-    println!("Hello, world!");
+enum Expr {
+    Id(String),
+    Int(i64),
+    Float(f64),
+    String(String),
+}
+
+fn main() {
+    let text = "3.14 \"foo\" false true ( ) + += /* 1 /* 2 */ 3 */  // 4 \n 5";
+    let lexer = Lexer::new(text);
+    lexer.for_each(|token| {
+        println!("{:?}", token);
+    })
 }