Selector operator, multi-operand, added

operand-expr.go

@@ -4,7 +4,7 @@
 // operand-expr.go
 package expr
 
-import "errors"
+import "fmt"
 
 // -------- expr term
 func newExprTerm(tk *Token) *term {
@@ -25,7 +25,7 @@ func evalExpr(ctx exprContext, self *term) (v any, err error) {
 	if expr, ok := self.value().(Expr); ok {
 		v, err = expr.Eval(ctx, false)
 	} else {
-		err = errors.New("invalid body of function definition")
+		err = fmt.Errorf("expression expected, got %T", self.value())
 	}
 	return
 }