Add variable declarations

examples/hello_world.fx

@@ -1,8 +1,9 @@
 // This is a comment
 
 fn main() {
+    let x = 2;
+    let y;
     return 1;
-    
 }
 
 fn fib() {}

src/lexer/mod.rs

@@ -43,9 +43,9 @@ pub enum TokenKind {
     /// ";"
     SemiColon,
     /// "="
-    Equals,
+    Assign,
     /// "=="
-    DeepEquals,
+    Equals,
     /// "<"
     SmallerThen,
     /// ">"
@@ -147,8 +147,8 @@ impl Cursor<'_> {
                 _ => Slash,
             },
             '=' => match self.first() {
-                '=' => DeepEquals,
+                '=' => Equals,
-                _ => Equals,
+                _ => Assign,
             },
             ':' => Colon,
             ';' => SemiColon,

src/lexer/tests.rs

@@ -28,7 +28,7 @@ mod tests {
             tokens.nth(0).unwrap(),
             Token {
                 len: 1,
-                kind: TokenKind::Equals,
+                kind: TokenKind::Assign,
                 raw: "=".to_owned()
             }
         );
@@ -69,7 +69,7 @@ mod tests {
             tokens.nth(0).unwrap(),
             Token {
                 len: 1,
-                kind: TokenKind::Equals,
+                kind: TokenKind::Assign,
                 raw: "=".to_owned()
             }
         );

src/parser/mod.rs

@@ -146,6 +146,12 @@ impl Parser {
         let token = self.next_token();
         println!("parse_statement: {:?}", token);
         match token.kind {
+            TokenKind::Keyword(Keyword::Let) => {
+                let state = self.parse_declare();
+                self.match_token(TokenKind::SemiColon)?;
+
+                state
+            }
             TokenKind::Keyword(Keyword::Return) => {
                 let state = Statement::Return(self.parse_expression()?);
                 self.match_token(TokenKind::SemiColon)?;
@@ -166,6 +172,23 @@ impl Parser {
             other => Err(format!("Expected Expression, found {:?}", other)),
         }
     }
+
+    fn parse_declare(&mut self) -> Result<Statement, String> {
+        match (
+            self.next_token().kind,
+            self.peek().ok_or("Expected ; or =")?.kind,
+        ) {
+            (TokenKind::Identifier(name), TokenKind::SemiColon) => {
+                Ok(Statement::Declare(Variable { name }, None))
+            }
+            (TokenKind::Identifier(name), TokenKind::Assign) => {
+                self.drop(1);
+                let exp = self.parse_expression().ok();
+                Ok(Statement::Declare(Variable { name }, exp))
+            }
+            other => Err(format!("Expected identifier, found {:?}", other)),
+        }
+    }
 }
 
 pub fn parse(tokens: Vec<Token>) -> Result<node_type::Program, String> {