4 files changed, 139 insertions, 0 deletions
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..e2a3069
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/target
+*~
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..f04a31e
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "rusteqn"
+version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..e96d941
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "rusteqn"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..0bb1740
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,124 @@
+#[derive(Debug, PartialEq)]
+enum Token {
+    Number(f64),
+    Operator(char),
+    Function(String),
+    Variable(String),
+    RightParen,
+    LeftParen
+}
+
+#[derive(Debug, PartialEq)]
+enum TokenizerError {
+    TooManyDots(String),
+    ConstantNotFound(String),
+    BadCharacter(char)
+}
+
+fn str_to_const(s: &str) -> Option<f64> {
+    match s {
+	"PI" => Some(std::f64::consts::PI),
+	"E" => Some(std::f64::consts::E),
+	_ => None
+    }
+}
+
+fn tokenize(input: &str) -> Result<Vec<Token>, TokenizerError> {
+    let mut tokens = Vec::new();
+    let mut chars = input.chars().peekable();
+
+    while let Some(&ch) = chars.peek() {
+	match ch {
+	    '0'..='9' => {
+		let mut num = String::new();
+		let mut has_dot = false;
+		while let Some(&c) = chars.peek() {
+		    if c.is_ascii_digit() || (c == '.' && !has_dot) {
+			num.push(c);
+			chars.next();
+			has_dot |= c == '.';
+		    } else if c == '.' && has_dot {
+			return Err(TokenizerError::TooManyDots(num));
+		    } else {
+			break;
+		    }
+		}
+		tokens.push(Token::Number(num.parse().unwrap()));
+	    }
+
+	    '+' | '-' | '*' | '/' | '%' | '^' => {
+		chars.next();
+		tokens.push(Token::Operator(ch));
+	    }
+
+	    'a'..='z' | '_' => {
+		let mut pt: Option<Token> = None;
+		let mut s = String::new();
+		while let Some(&c) = chars.peek() {
+		    match c {
+			'a'..='z' | 'A'..='Z' | '0'..='9' | '_' => {
+			    s.push(c);
+			    chars.next();
+			}
+
+			'(' => {
+			    pt = Some(Token::Function(s.clone()));
+			    break;
+			}
+
+			_ => {
+			    break;
+			}
+		    }
+		}
+		tokens.push(match pt {
+		    Some(token) => token,
+		    None => Token::Variable(s.clone())
+		});
+	    }
+
+	    'A'..='Z' => {
+		let mut s = String::new();
+		while let Some(&c @ ('A'..='Z' | '_')) = chars.peek() {
+		    s.push(c);
+		    chars.next();
+		}
+		let n = str_to_const(&s).ok_or(TokenizerError::ConstantNotFound(s))?;
+		tokens.push(Token::Number(n));
+	    }
+	    
+	    c if c.is_whitespace() || c == ',' => {
+		while let Some(&c) = chars.peek() {
+		    if c.is_whitespace() {
+			chars.next();
+		    } else {
+			break;
+		    }
+		}
+	    }
+
+	    '(' => {
+		chars.next();
+		tokens.push(Token::RightParen);
+	    }
+
+	    ')' => {
+		chars.next();
+		tokens.push(Token::LeftParen);
+	    }
+
+	    _ => {
+		return Err(TokenizerError::BadCharacter(ch));
+	    }
+	}
+    }
+
+    Ok(tokens)
+}
+
+fn main() {
+    let input = "x + 4 * (3 - sin((y+PI)) / 2.123)^2";
+    println!("{}", input);
+    let tokens = tokenize(input).unwrap();
+    println!("{:#?}", tokens);
+}