restructure parsing and typing modules

* parsing backend submodules
* move typing to its own module

src/ast/expr.rs

@@ -4,10 +4,15 @@ use crate::ast::*;
 pub enum Expr {
     BinaryExpression(Box<Expr>, BinaryOperator, Box<Expr>),
     Identifier(Identifier),
+    Call(Box<Call>),
+    // Literals
+    BooleanLiteral(bool),
     IntegerLiteral(i64),
     FloatLiteral(f64),
     StringLiteral(String),
-    Call(Box<Call>),
+    Block(Box<Block>),
+    /// Last field is either Expr::Block or Expr::IfExpr
+    IfExpr(Box<Expr>, Box<Block>, Box<Expr>),
 }
 
 #[derive(Debug, PartialEq, Clone)]
@@ -16,4 +21,7 @@ pub enum BinaryOperator {
     Sub,
     Mul,
     Div,
+    Modulo,
+    Equal,
+    NotEqual,
 }