From 108ebfba69207e0a293a33f4af0a6ea9dfe4a923 Mon Sep 17 00:00:00 2001
From: Mahmoud Abumandour <ma.mandourr@gmail.com>
Date: Sat, 2 Sep 2023 18:29:02 -0700
Subject: [PATCH] Support lexing integer literals

---
 Cargo.toml   |  3 +-
 src/lexer.rs | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs  |  4 ++-
 3 files changed, 87 insertions(+), 3 deletions(-)
 create mode 100644 src/lexer.rs

diff --git a/Cargo.toml b/Cargo.toml
index 22429b2..bf2acca 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,6 +3,5 @@ name = "rustyc"
 version = "0.1.0"
 edition = "2021"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
-
 [dependencies]
+rstest = "0.18.2"
\ No newline at end of file
diff --git a/src/lexer.rs b/src/lexer.rs
new file mode 100644
index 0000000..370433a
--- /dev/null
+++ b/src/lexer.rs
@@ -0,0 +1,83 @@
+pub struct Lexer {
+    src: String,
+    pos: usize,
+}
+#[derive(Debug, PartialEq, Eq)]
+enum TokenType {
+    Identifier,
+    Type,
+    Keyword,
+    Equals,
+    Plus,
+    SemiColon,
+    IntegerLiteral,
+    Eof,
+}
+
+#[derive(Debug)]
+pub struct Token {
+    value: String,
+    token_type: TokenType,
+    pos: usize,
+}
+
+static EOF: char = '\0';
+impl Lexer {
+
+    pub fn new(src: String) -> Self {
+        Self { src, pos: 0 }
+    }
+    fn consume(&mut self) -> char {
+        let curr = self.current();
+        self.pos += 1;
+        curr
+    }
+
+    fn current(&self) -> char {
+        if self.pos >= self.src.len() {
+            return EOF;
+        }
+
+        self.src.chars().nth(self.pos).unwrap()
+    }
+
+    fn lex_integer(&mut self) -> Token {
+        let mut value = String::new();
+        let start = self.pos;
+        let mut c = self.consume();
+        while c.is_digit(10) {
+            value.push(c);
+            c = self.consume();
+        }
+
+        Token { value, token_type: TokenType::IntegerLiteral, pos: start }
+    }
+
+    pub fn lex(&mut self) -> Vec<Token> {
+        let mut result = Vec::new();
+        loop {
+            let c = self.current();
+            if c == EOF { break; }
+            if c.is_digit(10) {
+                result.push(self.lex_integer());
+            }
+        }
+        result
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[rstest::rstest]
+    #[case("0")]
+    #[case("1")]
+    #[case("123")]
+    fn test_lex_integer(#[case] test_case: String) {
+        let tokens = Lexer::new(test_case.clone()).lex();
+        assert_eq!(1, tokens.len());
+        assert_eq!(test_case, tokens[0].value);
+        assert_eq!(TokenType::IntegerLiteral, tokens[0].token_type);
+    }
+}
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index e7a11a9..07601e7 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,5 @@
+mod lexer;
+
 fn main() {
-    println!("Hello, world!");
 }
+