Add parser, token stream, successfully parse let statement

src/lexer.rs

@@ -7,7 +7,7 @@ pub static EASIEST: &str = include_str!("../easiest.reid");
 
 static DECIMAL_NUMERICS: &[char] = &['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'];
 
-pub fn tokenize<T: Into<String>>(to_tokenize: T) -> Result<Vec<Token>, String> {
+pub fn tokenize<T: Into<String>>(to_tokenize: T) -> Result<Vec<FullToken>, String> {
     let to_tokenize = to_tokenize.into();
     let mut position = (0, 1);
     let mut cursor = Cursor {
@@ -17,7 +17,7 @@ pub fn tokenize<T: Into<String>>(to_tokenize: T) -> Result<Vec<Token>, String> {
 
     let mut tokens = Vec::new();
 
-    while let Some(character) = &cursor.consume() {
+    while let Some(character) = &cursor.next() {
         position.0 += 1;
         if *character == '\n' {
             position.1 += 1;
@@ -32,7 +32,7 @@ pub fn tokenize<T: Into<String>>(to_tokenize: T) -> Result<Vec<Token>, String> {
             // Comments
             '/' if peek == Some(&'/') => {
                 while !matches!(&cursor.peek(), Some('\n')) {
-                    cursor.consume();
+                    cursor.next();
                 }
                 continue;
             }
@@ -44,13 +44,13 @@ pub fn tokenize<T: Into<String>>(to_tokenize: T) -> Result<Vec<Token>, String> {
                         break;
                     }
                     value += &c.to_string();
-                    cursor.consume();
+                    cursor.next();
                 }
 
                 // Check for keywords
                 let variant = match value.as_str() {
-                    "let" => TokenVariant::LetKeyword,
-                    _ => TokenVariant::Identifier(value),
+                    "let" => Token::LetKeyword,
+                    _ => Token::Identifier(value),
                 };
                 variant
             }
@@ -62,13 +62,13 @@ pub fn tokenize<T: Into<String>>(to_tokenize: T) -> Result<Vec<Token>, String> {
                         break;
                     }
                     value += &c.to_string();
-                    cursor.consume();
+                    cursor.next();
                 }
-                TokenVariant::DecimalValue(value)
+                Token::DecimalValue(value)
             }
             // Single character tokens
-            '=' => TokenVariant::Equals,
-            ';' => TokenVariant::Semicolon,
+            '=' => Token::Equals,
+            ';' => Token::Semicolon,
             // Invalid token
             _ => Err(format!(
                 "Unknown token '{}' at {}, {}",
@@ -76,37 +76,40 @@ pub fn tokenize<T: Into<String>>(to_tokenize: T) -> Result<Vec<Token>, String> {
             ))?,
         };
 
-        tokens.push(Token { variant, position });
+        tokens.push(FullToken {
+            token: variant,
+            position,
+        });
     }
 
     position.0 += 1;
 
-    tokens.push(Token {
-        variant: TokenVariant::Eof,
+    tokens.push(FullToken {
+        token: Token::Eof,
         position,
     });
 
     Ok(tokens)
 }
 
-pub struct Token {
-    variant: TokenVariant,
+pub struct FullToken {
+    pub token: Token,
     position: Position,
 }
 
-impl Debug for Token {
+impl Debug for FullToken {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         f.write_fmt(format_args!(
             "{:?} (Ln {}, Col {})",
-            self.variant, self.position.1, self.position.0
+            self.token, self.position.1, self.position.0
         ))
     }
 }
 
 pub type Position = (u32, u32);
 
-#[derive(Debug)]
-pub enum TokenVariant {
+#[derive(Debug, Eq, PartialEq, Clone)]
+pub enum Token {
     LetKeyword,
     Semicolon,
     Equals,
@@ -122,7 +125,7 @@ pub struct Cursor<'a> {
 }
 
 impl<'a> Cursor<'a> {
-    fn consume(&mut self) -> Option<char> {
+    fn next(&mut self) -> Option<char> {
         let next = self.char_stream.next();
         self.position.0 += 1;
         if let Some('\n') = next {

src/main.rs

@@ -1,9 +1,13 @@
-use crate::lexer::EASIEST;
+use crate::{lexer::EASIEST, parser::LetStatement, token_stream::TokenStream};
 
 mod lexer;
+mod parser;
+mod token_stream;
 
 fn main() {
-    let token_stream = lexer::tokenize(EASIEST).unwrap();
+    let tokens = lexer::tokenize(EASIEST).unwrap();
+    let mut token_stream = TokenStream::from(&tokens);
 
-    dbg!(&token_stream);
+    dbg!(token_stream.parse::<LetStatement>().ok());
+    dbg!(token_stream.parse::<LetStatement>().ok());
 }

src/parser.rs

@@ -0,0 +1,47 @@
+use crate::{lexer::Token, token_stream::TokenStream};
+
+pub trait Parseable
+where
+    Self: std::marker::Sized,
+{
+    fn parse(stream: TokenStream) -> Result<Self, ()>;
+}
+
+#[derive(Debug)]
+pub enum Expression {
+    VariableName(String),
+    ContantI32(i32),
+}
+
+impl Parseable for Expression {
+    fn parse(mut stream: TokenStream) -> Result<Expression, ()> {
+        if let Some(token) = stream.next() {
+            Ok(match &token {
+                Token::Identifier(v) => Expression::VariableName(v.clone()),
+                Token::DecimalValue(v) => Expression::ContantI32(v.parse().unwrap()),
+                _ => Err(())?,
+            })
+        } else {
+            Err(())
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct LetStatement(String, Expression);
+
+impl Parseable for LetStatement {
+    fn parse(mut stream: TokenStream) -> Result<LetStatement, ()> {
+        stream.expect(Token::LetKeyword)?;
+
+        if let Some(Token::Identifier(variable)) = stream.next() {
+            stream.expect(Token::Equals)?;
+
+            let expression = stream.parse()?;
+            stream.expect(Token::Semicolon)?;
+            Ok(LetStatement(variable, expression))
+        } else {
+            Err(())
+        }
+    }
+}

src/token_stream.rs

@@ -0,0 +1,78 @@
+use crate::{
+    lexer::{FullToken, Token},
+    parser::Parseable,
+};
+
+pub struct TokenStream<'a, 'b> {
+    ref_position: Option<&'b mut usize>,
+    tokens: &'a [FullToken],
+    pub position: usize,
+}
+
+impl<'a, 'b> TokenStream<'a, 'b> {
+    pub fn from(tokens: &'a [FullToken]) -> Self {
+        TokenStream {
+            ref_position: None,
+            tokens,
+            position: 0,
+        }
+    }
+
+    pub fn expect(&mut self, token: Token) -> Result<(), ()> {
+        if let Some(peeked) = self.peek() {
+            if token == *peeked {
+                self.position += 1;
+                Ok(())
+            } else {
+                Err(())
+            }
+        } else {
+            Err(())
+        }
+    }
+
+    pub fn next(&mut self) -> Option<Token> {
+        let value = if self.tokens.len() < self.position {
+            None
+        } else {
+            Some(self.tokens[self.position].token.clone())
+        };
+        self.position += 1;
+        value
+    }
+
+    pub fn peek(&mut self) -> Option<&Token> {
+        if self.tokens.len() < self.position {
+            None
+        } else {
+            Some(&self.tokens[self.position].token)
+        }
+    }
+
+    pub fn parse<T: Parseable>(&mut self) -> Result<T, ()> {
+        let mut ref_pos = self.position;
+
+        let position = self.position;
+        let clone = TokenStream {
+            ref_position: Some(&mut ref_pos),
+            tokens: self.tokens,
+            position,
+        };
+
+        match T::parse(clone) {
+            Ok(res) => {
+                self.position = ref_pos.max(self.position);
+                Ok(res)
+            }
+            Err(e) => Err(e),
+        }
+    }
+}
+
+impl Drop for TokenStream<'_, '_> {
+    fn drop(&mut self) {
+        if let Some(ref_pos) = &mut self.ref_position {
+            **ref_pos = self.position;
+        }
+    }
+}