updated interpreter error and replaced parseExpr with the appropriate allowed expression

DEMO/Test/struct.ecla

@@ -67,3 +67,12 @@ p.printSelf(p);
 # access embedded struct fields
 console.println(p.test.test);
 
+# use a struct field in a binary operation
+var p2 int = p.x + p.y;
+console.println(p2);
+
+# use a field of a struct field in a binary operation
+var p3 string = p.test.test + p.test.test;
+console.println(p3);
+
+

interpreter/expr.go

@@ -572,7 +572,7 @@ func RunSelectorExpr(expr parser.SelectorExpr, env *Env, Struct eclaType.Type) [
 			}
 			return []*Bus{NewMainBus(*result)}
 		default:
-			env.ErrorHandle.HandleError(expr.StartLine(), expr.StartPos(), "struct cannot have filed of type "+prev.GetType(), errorHandler.LevelFatal)
+			env.ErrorHandle.HandleError(expr.StartLine(), expr.StartPos(), "struct cannot have field of type "+prev.GetType(), errorHandler.LevelFatal)
 		}
 	default:
 		env.ErrorHandle.HandleError(expr.StartLine(), expr.StartPos(), "type "+prev.GetType()+" has no fields", errorHandler.LevelFatal)

parser/Parser.go

@@ -951,7 +951,21 @@ func (p *Parser) ParseSelector(x Expr) Expr {
 		p.HandleFatal("Expected field name after '.'")
 		return nil
 	}
-	selector := p.ParseExpr()
+	// check if the field is a function call
+	var selector Expr
+	if p.Peek(1).TokenType == lexer.LPAREN {
+		selector = p.ParseFunctionCallExpr()
+	} else {
+		selector = p.ParseVariableAccess()
+		p.Step()
+	}
+	// check if there is a period after the selector to see if it is a selector
+	if p.CurrentToken.TokenType == lexer.PERIOD {
+		p.Step()
+		selectorDepth++
+		selector = p.ParseSelector(selector)
+		selectorDepth--
+	}
 	return SelectorExpr{Field: p.CurrentToken, Expr: x, Sel: selector}
 }
 

parser/Parser_test.go

@@ -1335,6 +1335,23 @@ func TestParser_ParseSelector(t *testing.T) {
 	}
 	ok = false
 
+	// selector with a function call
+	resetWithTokens(&par, lexer.Lexer("test.test()"))
+	par.MultiStep(2)
+	par.ParseSelector(nil)
+	if ok {
+		t.Errorf("ParseSelector() raised an error when it should not")
+	}
+	ok = false
+	// selector used in a binary expression
+	resetWithTokens(&par, lexer.Lexer("test.test + 1"))
+	par.MultiStep(2)
+	par.ParseSelector(nil)
+	if ok {
+		t.Errorf("ParseSelector() raised an error when it should not")
+	}
+	ok = false
+
 	e.RestoreExit()
 }