cursor: refactor to only work on strings

src/error.rs

@@ -1,27 +1,27 @@
-use std::fmt;
-use std::fmt::Formatter;
+use std::{fmt, io};
+
 use crate::ast::tree::Type;
+use crate::lex::token::Position;
 
 /// This is just a wrapper for the actual error types.
 /// I have no idea whether this is good design (probably not),
 /// but idc for now.  Shouldn't be too hard to change the API
 /// later on bc each component of the compiler has its own
 /// wrappers for instantiating errors anyway.
-#[derive(Debug)]
 pub struct Error {
     e: Box<dyn ErrorDetails>,
 }
 
 impl Error {
-    pub fn syntax_error(file: String, line: usize, col: usize, msg: String) -> Error {
+    pub fn syntax_error(pos: Position, msg: String) -> Error {
         Error {
-            e: Box::new(SyntaxError::new(file, line, col, msg))
+            e: Box::new(SyntaxError::new(pos, msg)),
         }
     }
 
-    pub fn type_error(file: String, line: usize, col: usize, expected: Type, actual: Type) -> Error {
+    pub fn type_error(pos: Position, expected: Type, actual: Type) -> Error {
         Error {
-            e: Box::new(TypeError::new(file, line, col, expected, actual))
+            e: Box::new(TypeError::new(pos, expected, actual)),
         }
     }
 
@@ -56,13 +56,6 @@ trait ErrorDetails {
     fn name(&self) -> &str;
 }
 
-#[derive(Debug)]
-struct Position {
-    file: String,
-    line: usize,
-    col: usize,
-}
-
 #[derive(Debug)]
 pub struct SyntaxError {
     pos: Position,
@@ -72,31 +65,35 @@ pub struct SyntaxError {
 #[derive(Debug)]
 pub struct TypeError {
     pos: Position,
-    expected: Type,
-    actual: Type,
+    msg: String,
 }
 
-impl fmt::Display for dyn ErrorDetails {
-    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        write!(f, "{} in {}:{}:{}: {}", self.name(), self.file(), self.line(), self.col(), self.msg())
+impl fmt::Debug for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let e = &self.e;
+        write!(
+            f,
+            "{} in {}:{}:{}: {}",
+            e.name(),
+            e.file(),
+            e.line(),
+            e.col(),
+            e.msg()
+        )
     }
 }
 
 impl SyntaxError {
-    pub fn new(file: String, line: usize, col: usize, msg: String) -> SyntaxError {
-        SyntaxError {
-            pos: Position { file, line, col },
-            msg,
-        }
+    pub fn new(pos: Position, msg: String) -> SyntaxError {
+        SyntaxError { pos, msg }
     }
 }
 
 impl TypeError {
-    pub fn new(file: String, line: usize, col: usize, expected: Type, actual: Type) -> TypeError {
+    pub fn new(pos: Position, expected: Type, actual: Type) -> TypeError {
         TypeError {
-            pos: Position { file, line, col },
-            expected,
-            actual,
+            pos,
+            msg: format!("Expected type {}, got {} instead", expected, actual),
         }
     }
 }
@@ -137,7 +134,7 @@ impl ErrorDetails for TypeError {
     }
 
     fn msg(&self) -> &String {
-        &format!("Expected type {}, got {} instead", self.expected, self.actual)
+        &self.msg
     }
 
     fn name(&self) -> &str {

src/lex/cursor.rs

@@ -1,52 +1,41 @@
-use std::str::Chars;
-
-/// A cursor for iterating over individual characters in a stream.
-/// Supports backwards seeking.
-pub struct Cursor<'a> {
-    stream: Chars<'a>,
-    offset: usize,            // where we pull our characters from
-    history: Vec<char>, // how many chars we are behind the stream position (when seeking back)
-    line_lengths: Vec<usize>, // complete list of all characters we've read so far
-    line: usize,        // length of all previous lines (for seeking back)
-    col: usize,         // current line (starting from 1)
-    pos: usize,         // current column in line (starting from 1)
-    chop: usize,
-    current: Option<char>,
+/// Convenience helper for iterating over the characters in a string.
+/// Supports backwards seeking and tracks line/column numbers.
+pub struct Cursor {
+    raw: Vec<char>,           // array of all characters
+    pos: usize,               // index (in `raw`) of the *next* character to be read
+    line_lengths: Vec<usize>, // previous line lengths (for seeking back)
+    line: usize,              // current line (counting from 1)
+    col: usize,               // current column (counting from 1)
+    chop: usize,              // value of `pos` when `chop()` was called the last time
+    current: Option<char>,    // current character
 }
 
-impl Iterator for Cursor<'_> {
+impl Iterator for Cursor {
     type Item = char;
 
     fn next(&mut self) -> Option<char> {
-        let c = if self.offset > 0 {
-            let tmp = self.history[self.history.len() - self.offset];
-            self.offset -= 1;
-            tmp
-        } else {
-            let tmp = self.stream.next()?;
-            self.history.push(tmp);
-            tmp
-        };
+        if self.pos < self.raw.len() {
+            let c = self.raw[self.pos];
+            self.pos += 1;
 
-        self.current = Some(c);
+            if c == '\n' {
+                self.new_line();
+            } else {
+                self.col += 1;
+            }
 
-        if c == '\n' {
-            self.new_line();
+            self.current = Some(c);
+            Some(c)
         } else {
-            self.col += 1;
+            None
         }
-        self.pos += 1;
-
-        Some(c)
     }
 }
 
-impl<'a> Cursor<'a> {
-    pub fn new(stream: Chars<'a>) -> Cursor<'a> {
+impl Cursor {
+    pub fn new(raw: String) -> Cursor {
         Cursor {
-            stream,
-            offset: 0,
-            history: Vec::new(),
+            raw: Vec::from_iter(raw.chars()),
             line_lengths: Vec::new(),
             line: 1,
             col: 0, // increments in first call to next()
@@ -58,18 +47,20 @@ impl<'a> Cursor<'a> {
 
     /// Reverse the cursor by a single character.
     pub fn prev(&mut self) -> Option<char> {
-        if self.history.len() == 0 {
-            None
-        } else {
-            self.offset += 1;
-            let c = self.history[self.history.len() - self.offset];
+        if self.pos > 0 {
+            self.pos -= 1;
+            let c = self.raw[self.pos];
+
             if self.col == 0 {
                 self.prev_line();
             } else {
                 self.col -= 1;
             }
-            self.pos -= 1;
+
+            self.current = Some(c);
             Some(c)
+        } else {
+            None
         }
     }
 
@@ -103,22 +94,20 @@ impl<'a> Cursor<'a> {
 
     /// Return the next character without actually advancing the cursor.
     pub fn peek(&mut self) -> Option<char> {
-        if self.offset > 0 {
-            Some(self.history[self.history.len() - self.offset])
-        } else {
-            let c = self.next()?;
-            self.prev();
-            Some(c)
-        }
+        let c = self.next()?;
+        self.prev();
+        Some(c)
     }
 
     pub fn skip_whitespace(&mut self) {
         self.seek_while(|c| c.is_ascii_whitespace());
     }
 
+    /// Return a string of every character since
+    /// the last time this method was called.
     pub fn chop(&mut self) -> String {
         assert!(self.pos >= self.chop);
-        let s = String::from_iter(self.history[self.chop..self.pos].into_iter());
+        let s = String::from_iter(self.raw[self.chop..self.pos].into_iter());
         self.chop = self.pos;
         s
     }
@@ -149,7 +138,7 @@ impl<'a> Cursor<'a> {
 
     fn prev_line(&mut self) {
         assert!(self.line > 0);
-        assert!(self.col == 0);
+        assert_eq!(self.col, 0);
         self.col = self.line_lengths.pop().unwrap();
         self.line -= 1;
     }

src/lex/mod.rs

@@ -1,16 +1,14 @@
-use std::str::Chars;
-
 mod cursor;
 use cursor::Cursor;
 
 pub(crate) mod token;
-use token::Token;
+use token::{Position, Token};
 
 use crate::error::Error;
 
-pub struct Lexer<'a> {
+pub struct Lexer {
     file: String,
-    cursor: Cursor<'a>,
+    cursor: Cursor,
     history: Vec<Token>,
     offset: usize,
     token_line: usize,
@@ -27,6 +25,7 @@ struct KeywordMap {
 }
 
 const fn kw(raw: &'static str, kind: token::Kind) -> KeywordMap {
+    assert!(raw.len() >= 2);
     KeywordMap { raw, kind }
 }
 
@@ -39,7 +38,7 @@ static KEYWORDS: [KeywordMap; 6] = [
     kw("type", token::Kind::TypeKeyword),
 ];
 
-impl Iterator for Lexer<'_> {
+impl Iterator for Lexer {
     type Item = Result<Token, Error>;
 
     fn next(&mut self) -> Option<Result<Token, Error>> {
@@ -70,7 +69,8 @@ impl Iterator for Lexer<'_> {
             '%' => self.token_ok(token::Kind::Percent),
 
             '#' => {
-                self.read_comment().unwrap(); // this can't fail
+                // this can't fail
+                self.read_comment().unwrap();
                 // we don't need comments for now and they would
                 // only confuse the parser so let's just Not
                 self.next()?
@@ -90,11 +90,11 @@ impl Iterator for Lexer<'_> {
     }
 }
 
-impl<'a> Lexer<'a> {
-    pub fn new(file: String, stream: Chars<'a>) -> Lexer<'a> {
+impl Lexer {
+    pub fn new(filename: String, raw: String) -> Lexer {
         Lexer {
-            file,
-            cursor: Cursor::new(stream),
+            file: filename,
+            cursor: Cursor::new(raw),
             history: Vec::new(),
             offset: 0,
             token_line: 1,
@@ -123,12 +123,18 @@ impl<'a> Lexer<'a> {
     }
 
     pub fn expect_kind(&mut self, kind: token::Kind) -> Result<Token, Error> {
+        self.expect_kinds(&[kind])
+    }
+
+    pub fn expect_kinds(&mut self, kinds: &[token::Kind]) -> Result<Token, Error> {
         match self.next() {
-            Some(Ok(t)) => if t.kind == kind {
-                Ok(t)
-            } else {
-                self.syntax_error(format!("Expected {}, got {}", kind, t.kind))
-            },
+            Some(Ok(t)) => {
+                if kinds.contains(&t.kind) {
+                    Ok(t)
+                } else {
+                    self.syntax_error(format!("Expected one of {:?}, got {}", kinds, t.kind))
+                }
+            }
             Some(Err(e)) => Err(e),
             None => self.syntax_error(String::from("Unexpected EOF")),
         }
@@ -189,7 +195,7 @@ impl<'a> Lexer<'a> {
     }
 
     fn read_prefix_int_literal(&mut self) -> Result<Token, Error> {
-        assert_eq!(self.cursor.next(), Some('0'));
+        assert_eq!(self.cursor.current(), Some('0'));
         match self.cursor.next() {
             Some('x') => self.read_int_literal(16),
             Some('o') => self.read_int_literal(8),
@@ -215,8 +221,11 @@ impl<'a> Lexer<'a> {
     fn token(&mut self, kind: token::Kind, raw: String) -> Token {
         let t = Token {
             kind,
-            line: self.token_line,
-            col: self.token_col,
+            pos: Position {
+                file: self.file.clone(),
+                line: self.token_line,
+                col: self.token_col,
+            },
             raw,
         };
         self.token_line = self.cursor.line();
@@ -248,10 +257,12 @@ impl<'a> Lexer<'a> {
 
     fn syntax_error<T>(&mut self, msg: String) -> Result<T, Error> {
         Err(Error::syntax_error(
-            self.file.clone(),
-            self.cursor.line(),
-            self.cursor.col(),
-            msg
+            Position {
+                file: self.file.clone(),
+                line: self.cursor.line(),
+                col: self.cursor.col(),
+            },
+            msg,
         ))
     }
 }

src/lex/token.rs

@@ -4,14 +4,18 @@ use std::fmt;
 #[derive(Debug, Clone)]
 pub struct Token {
     pub kind: Kind,
-    /// line of the first character (starting from 1)
-    pub line: usize,
-    /// column of the first character (starting from 1)
-    pub col: usize,
+    pub pos: Position,
     /// raw text
     pub raw: String,
 }
 
+#[derive(Debug, Clone)]
+pub struct Position {
+    pub file: String,
+    pub line: usize,
+    pub col: usize,
+}
+
 impl fmt::Display for Token {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "{}: \"{}\"", self.kind, self.raw)

src/main.rs

@@ -7,7 +7,7 @@ mod error;
 
 fn main() {
     let s = fs::read_to_string("test.gaybuild").unwrap();
-    let lexer = Lexer::new(String::from("test.gaybuild"), s.chars());
+    let lexer = Lexer::new(String::from("test.gaybuild"), s);
     for token in lexer {
         println!("{}", token.unwrap());
     }