add assignment to struct fields

examples/hello.v

@@ -46,5 +46,7 @@ fn main(a int) int {
 		y: 20 
 	} 
 
+	p.x = 69
+
 	println(egg.scramble(3).with(cheddar)) 
 }

src/ast.zig

@@ -81,6 +81,7 @@ pub const ExprType = enum {
 
     Grouping,
     Get,
+    Set,
 };
 
 pub const VarDecl = struct {
@@ -111,6 +112,12 @@ pub const GetExpr = struct {
     name: Token,
 };
 
+pub const SetExpr = struct {
+    struc: *Expr,
+    field: Token,
+    value: *Expr,
+};
+
 pub const Expr = union(ExprType) {
     Assign: AssignExpr,
     VarDecl: VarDecl,
@@ -124,7 +131,9 @@ pub const Expr = union(ExprType) {
     Variable: Token,
     Grouping: *Expr,
     Call: CallExpr,
+
     Get: GetExpr,
+    Set: SetExpr,
 };
 
 pub const Block = std.ArrayList(*Stmt);

src/ast_printer.zig

@@ -185,6 +185,14 @@ pub fn printExpr(expr: *Expr) void {
             warn(".{})", get.name.lexeme);
         },
 
+        .Set => |set| {
+            warn("(set ");
+            printExpr(set.struc);
+            warn(" {} ", set.field.lexeme);
+            printExpr(set.value);
+            warn(")");
+        },
+
         else => std.debug.warn("UnknownExpr-{}", @tagName(expr.*)),
     }
 }

src/parser.zig

@@ -287,6 +287,19 @@ pub const Parser = struct {
         return expr;
     }
 
+    fn mkSet(self: *@This(), struc: *Expr, field: Token, value: *Expr) !*Expr {
+        var expr = try self.allocator.create(Expr);
+        expr.* = Expr{
+            .Set = ast.SetExpr{
+                .struc = struc,
+                .field = field,
+                .value = value,
+            },
+        };
+
+        return expr;
+    }
+
     fn mkBool(self: *Parser, val: bool) !*ast.Expr {
         var expr = try self.allocator.create(Expr);
         expr.* = Expr{
@@ -598,16 +611,29 @@ pub const Parser = struct {
             _ = try self.nextToken();
             value = try self.parseAssignment();
 
-            if (ast.ExprType(expr.*) != .Variable) {
-                self.doError("Invalid assignment target");
-                return Result.CompileError;
-            }
-
+            switch (expr.*) {
+                .Variable => {
                     switch (op.ttype) {
                         .ColonEqual => return try self.mkVarDecl(expr.Variable, value, mutable),
                         .Equal => return try self.mkAssign(expr.Variable, value),
                         else => unreachable,
                     }
+                },
+
+                .Get => |get| {
+                    if (op.ttype == .ColonEqual) {
+                        self.doError("can not initialize struct field");
+                        return Result.CompileError;
+                    }
+
+                    return try self.mkSet(get.struc, get.name, value);
+                },
+
+                else => |expr_typ| {
+                    self.doError("Invalid assignment target {}", expr_typ);
+                    return Result.CompileError;
+                },
+            }
         }
 
         return expr;