- implementation of <var> <op> = <expr> type statements such as `x +=

5`
- implementation of logical and shift operations in parser and codegen.
- implementation of sizeof keyword as unary operator

in progress (non functional)
- implementation of prefix and postfix inc/dec operators

- array access by index (implemented, untested as arrays aren't
  implemented yet). essentially just a pointer write with offset.
- struct/member access (parsing implemented, untested.)

compiler/src/model.rs

@@ -11,6 +11,7 @@ pub enum CompilerError {
     Generic(String),
     UnknownType,
     TypeMismatch(TypeId, TypeId),
+    Unimplemented(String),
 }
 
 #[derive(Debug, PartialEq, Eq, Clone)]
@@ -130,6 +131,7 @@ pub enum Statement {
     },
     Assign {
         varname: String,
+        operator: AssignmentOperator,
         value: Expression,
     },
     PtrWrite {
@@ -308,6 +310,21 @@ impl Expression {
     }
 }
 
+#[derive(Debug, Clone, PartialEq)]
+pub enum AssignmentOperator {
+    Assign,
+    AddAssign,
+    SubAssign,
+    MulAssign,
+    DivAssign,
+    ModAssign,
+    AndAssign,
+    OrAssign,
+    XorAssign,
+    LeftShiftAssign,
+    RightShiftAssign,
+}
+
 #[allow(unused)]
 #[derive(Debug, Clone, PartialEq)]
 pub enum BinaryOperator {
@@ -371,7 +388,6 @@ pub enum UnaryOperator {
     Minus,
     AddressOf,
     Dereference,
-    CastAs,
     BitwiseNot,
     LogicalNot,
     Increment,
@@ -388,7 +404,6 @@ impl fmt::Display for UnaryOperator {
             Self::Minus => write!(f, "-"),
             Self::Dereference => write!(f, "*"),
             Self::AddressOf => write!(f, "&"),
-            Self::CastAs => write!(f, "as"),
             Self::BitwiseNot => write!(f, "~"),
             Self::LogicalNot => write!(f, "!"),
             Self::SizeOf => write!(f, "sizeof"),