add cursor helper

src/lex/cursor.rs

@@ -0,0 +1,90 @@
+// See the end of this file for copyright and license terms.
+
+use std::str::Chars;
+
+pub(crate) struct Cursor<'a> {
+    stream: Chars<'a>,
+    line: usize,
+    col: usize,
+}
+
+impl<'a> Cursor<'a> {
+    pub const fn new(stream: Chars<'a>) -> Cursor<'a> {
+        Cursor {
+            stream: stream,
+            line: 1,
+            col: 1,
+        }
+    }
+
+    pub fn next(&mut self) -> Option<char> {
+        let c = self.stream.next();
+
+        self.col += 1;
+        if c == Some('\n') {
+            self.line += 1;
+            self.col = 0;
+        }
+
+        c
+    }
+
+    pub fn advance_by(&mut self, n: usize) -> Result<(), usize> {
+        for i in 0..n {
+            if self.next() == None {
+                return Err(i)
+            }
+        }
+
+        Ok(())
+    }
+
+    pub fn next_until(&mut self, test: fn (c: char) -> bool) -> String {
+        let mut s = String::new();
+    
+        for _ in 0.. {
+            match self.peek() {
+                Some(c) => if test(c) {
+                    break;
+                } else {
+                    s.push(c);
+                    self.next();
+                },
+                None => break,
+            }
+        }
+
+        s
+    }
+
+    pub fn peek(&self) -> Option<char> {
+        self.nth(1)
+    }
+
+    pub fn nth(&self, n: usize) -> Option<char> {
+        self.chars().nth(n)
+    }
+
+    pub fn line(&self) -> usize {
+        self.line
+    }
+
+    pub fn col(&self) -> usize {
+        self.col
+    }
+
+    pub fn chars(&self) -> Chars<'a> {
+        self.stream.clone()
+    }
+}
+
+// Copyright (C) 2021 Fefie <owo@fef.moe>
+// This file is part of gayconf.
+//
+// gayconf is ethical software: you can use, redistribute,
+// and/or modify it under the terms of the CNPLv5+ as found
+// in the LICENSE file in the source code root directory or
+// at <https://git.pixie.town/thufie/CNPL>.
+//
+// gayconf comes with ABSOLUTELY NO WARRANTY, to the extent
+// permitted by applicable law.  See the CNPL for details.