work

src/parser/v3/token/cursor.rs

@@ -0,0 +1,68 @@
+use std::{iter::Peekable, str::Chars};
+
+use super::super::ParserError;
+use super::FilePos;
+
+pub struct CharCursor<'a> {
+    chars: Peekable<Chars<'a>>,
+    next_pos: FilePos,
+    prev_pos: FilePos,
+}
+
+impl CharCursor<'_> {
+    pub fn next(&mut self) -> Option<char> {
+        let res = self.peek()?;
+        self.advance();
+        Some(res)
+    }
+    pub fn expect(&mut self, c: char) -> Result<(), ParserError> {
+        let next = self.expect_next()?;
+        if next == c {
+            Ok(())
+        } else {
+            Err(ParserError::at(
+                self.prev_pos,
+                format!("unexpected char '{next}'; expected '{c}'"),
+            ))
+        }
+    }
+    pub fn skip_whitespace(&mut self) {
+        while self.peek().is_some_and(|c| c.is_whitespace()) {
+            self.advance();
+        }
+    }
+    pub fn peek(&mut self) -> Option<char> {
+        self.chars.peek().copied()
+    }
+    pub fn advance(&mut self) {
+        let Some(next) = self.chars.next() else {
+            return;
+        };
+        self.prev_pos = self.next_pos;
+        if next == '\n' {
+            self.next_pos.col = 0;
+            self.next_pos.line += 1;
+        } else {
+            self.next_pos.col += 1;
+        }
+    }
+    pub fn expect_next(&mut self) -> Result<char, ParserError> {
+        self.next().ok_or(ParserError::unexpected_end())
+    }
+    pub fn next_pos(&self) -> FilePos {
+        self.next_pos
+    }
+    pub fn prev_pos(&self) -> FilePos {
+        self.prev_pos
+    }
+}
+
+impl<'a> From<&'a str> for CharCursor<'a> {
+    fn from(value: &'a str) -> Self {
+        Self {
+            chars: value.chars().peekable(),
+            next_pos: FilePos::start(),
+            prev_pos: FilePos::start(),
+        }
+    }
+}