Add token reader and access to last token in checker function

Signed-off-by: trivernis <trivernis@protonmail.com>

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "charred"
-version = "2.0.0"
+version = "2.1.0"
 authors = ["trivernis <trivernis@protonmail.com>"]
 edition = "2018"
 license-file = "LICENSE"

src/lexer.rs

@@ -1,6 +1,6 @@
 use crate::error::TapeResult;
 use crate::input_reader::InputReader;
-use crate::token::{Token, TokenCheckerFn, UnknownToken};
+use crate::token::{EOFToken, Token, TokenCheckerFn, UnknownToken};
 
 pub struct Lexer {
     reader: InputReader,
@@ -22,7 +22,7 @@ impl Lexer {
             let mut found = false;
 
             for checker_fn in &self.checkers {
-                if let Some(token) = checker_fn.as_ref()(&mut self.reader).await? {
+                if let Some(token) = checker_fn.as_ref()(&mut self.reader, tokens.last()).await? {
                     tokens.push(token);
                     found = true;
                     break;
@@ -34,6 +34,7 @@ impl Lexer {
                 tokens.push(Token::new(UnknownToken(self.reader.consume().await?)))
             }
         }
+        tokens.push(Token::new(EOFToken));
 
         Ok(tokens)
     }

src/lib.rs

@@ -2,6 +2,7 @@ pub mod error;
 pub mod input_reader;
 pub mod lexer;
 pub mod token;
+pub mod token_reader;
 
 #[cfg(test)]
 mod tests;

src/tests/mod.rs

@@ -1,3 +1,4 @@
 mod test_input;
 mod test_lexer;
 mod test_token;
+mod test_token_reader;

src/tests/test_lexer.rs

@@ -52,9 +52,9 @@ async fn parse_string_token(reader: &mut InputReader) -> TapeResult<Option<Token
 #[tokio::test]
 async fn it_scans() {
     let checkers: Vec<TokenCheckerFn> = vec![
-        Arc::new(|reader| Box::pin(parse_number_token(reader))),
+        Arc::new(|reader, _| Box::pin(parse_number_token(reader))),
-        Arc::new(|reader| Box::pin(parse_whitespace_token(reader))),
+        Arc::new(|reader, _| Box::pin(parse_whitespace_token(reader))),
-        Arc::new(|reader| Box::pin(parse_string_token(reader))),
+        Arc::new(|reader, _| Box::pin(parse_string_token(reader))),
     ];
     let input_reader = InputReader::new(Cursor::new("The Alphabet 12 ok"));
     let mut lexer = Lexer::new(input_reader, checkers);
@@ -75,8 +75,8 @@ async fn it_scans() {
 #[tokio::test]
 async fn it_falls_back_to_unknown() {
     let checkers: Vec<TokenCheckerFn> = vec![
-        Arc::new(|reader| Box::pin(parse_number_token(reader))),
+        Arc::new(|reader, _| Box::pin(parse_number_token(reader))),
-        Arc::new(|reader| Box::pin(parse_string_token(reader))),
+        Arc::new(|reader, _| Box::pin(parse_string_token(reader))),
     ];
     let input_reader = InputReader::new(Cursor::new("The Alphabet 12 ok"));
     let mut lexer = Lexer::new(input_reader, checkers);

src/tests/test_token_reader.rs

@@ -0,0 +1,57 @@
+use crate::token::{EOFToken, Token};
+use crate::token_reader::TokenReader;
+
+struct AToken;
+struct BToken;
+struct CToken;
+
+fn get_reader() -> TokenReader {
+    let tokens = vec![
+        Token::new(AToken),
+        Token::new(BToken),
+        Token::new(AToken),
+        Token::new(CToken),
+        Token::new(CToken),
+        Token::new(EOFToken),
+    ];
+
+    TokenReader::new(tokens)
+}
+
+#[test]
+fn peek_does_not_consume() {
+    let reader = get_reader();
+
+    assert!(reader.peek_is::<AToken>());
+    assert!(!reader.peek_is::<BToken>());
+    assert!(reader.peek_is::<AToken>());
+}
+
+#[test]
+fn consume_does_consume() {
+    let mut reader = get_reader();
+    assert!(reader.consume_as::<AToken>().is_some());
+    assert!(reader.consume_as::<BToken>().is_some());
+    assert!(reader.consume_as::<AToken>().is_some());
+    assert!(reader.consume_as::<CToken>().is_some());
+}
+
+#[test]
+fn check_eof_works() {
+    let mut reader = get_reader();
+    reader.seek(4);
+    assert!(!reader.check_eof());
+    reader.seek(5);
+    assert!(reader.check_eof());
+}
+#[test]
+fn peek_and_consume_returns_eof_on_input_end() {
+    let mut reader = get_reader();
+    reader.seek(4);
+    assert!(reader.consume_as::<EOFToken>().is_none());
+    assert!(reader.consume_as::<EOFToken>().is_some());
+    assert!(reader.consume_as::<EOFToken>().is_some());
+    assert!(reader.consume_as::<EOFToken>().is_some());
+    reader.seek(0);
+    assert!(reader.consume_as::<EOFToken>().is_none());
+}

src/token.rs

@@ -8,6 +8,7 @@ use std::sync::Arc;
 pub type TokenCheckerFn = Arc<
     dyn for<'a> Fn(
             &'a mut InputReader,
+            Option<&'a Token>, // last token
         ) -> Pin<Box<dyn Future<Output = TapeResult<Option<Token>>> + Send + 'a>>
         + Send
         + Sync,
@@ -45,3 +46,6 @@ impl Token {
 
 /// Parsed when no other matching token was found for the character
 pub struct UnknownToken(pub char);
+
+/// End Of File Token
+pub struct EOFToken;

src/token_reader.rs

@@ -0,0 +1,64 @@
+use crate::token::{EOFToken, Token};
+
+pub struct TokenReader {
+    tokens: Vec<Token>,
+    index: usize,
+    eof: Token,
+}
+
+impl TokenReader {
+    /// Creates a new token reader
+    pub fn new(mut tokens: Vec<Token>) -> Self {
+        if tokens.last().is_none() || !tokens.last().unwrap().is::<EOFToken>() {
+            // ensure that the last token always is an EOF Token
+            tokens.push(Token::new(EOFToken));
+        }
+        Self {
+            tokens,
+            index: 0,
+            eof: Token::new(EOFToken),
+        }
+    }
+
+    /// Peeks the next token
+    #[inline]
+    pub fn peek(&self) -> &Token {
+        self.tokens.get(self.index).unwrap_or(&self.eof)
+    }
+
+    /// Checks if the next token is of a specific type without consuming it
+    #[inline]
+    pub fn peek_is<T: 'static>(&self) -> bool {
+        self.peek().is::<T>()
+    }
+
+    /// Peeks the next token and tries to return is as a concrete type
+    #[inline]
+    pub fn peek_as<T: 'static>(&self) -> Option<&T> {
+        self.peek().try_as::<T>()
+    }
+
+    /// Consumes the next token and returns it
+    pub fn consume(&mut self) -> &Token {
+        self.index += 1;
+        self.tokens.get(self.index - 1).unwrap_or(&self.eof)
+    }
+
+    /// Consumes the next token and tries to return it as the specified type
+    #[inline]
+    pub fn consume_as<T: 'static>(&mut self) -> Option<&T> {
+        self.consume().try_as::<T>()
+    }
+
+    /// Seeks to the given index
+    #[inline]
+    pub fn seek(&mut self, to_index: usize) {
+        self.index = to_index
+    }
+
+    /// Returns if EOF has been reached
+    #[inline]
+    pub fn check_eof(&self) -> bool {
+        self.peek_is::<EOFToken>()
+    }
+}