Cannot assign to a readonly variable or a value

gistfile1.txt

[melezhik@e23f8de28e56 Sparrow6]$ perl6 -MSparrow6 -e 'Sparrow6::Runner.new( root => "/home/melezhik/sparrow/plugins/public/templater/", debug =>
True ).task-run' --ll-exception
[load plugin configuration] >>> [/home/melezhik/sparrow/plugins/public/templater//suite.yaml]
[parse plugin configuration] >>> [${:foo(${:bar($["a", "b", "c", "d"])}), :mode(644)}]
[input parameters] >>> [Hash]
Cannot assign to a readonly variable or a value
  in method task-run at /home/melezhik/.perl6/sources/58A2D16AF627CCE8CC3EBB21DDEBA29E2E38F9D9 (Sparrow6) line 37
  in block <unit> at -e line 1


/home/melezhik/.perl6/sources/58A2D16AF627CCE8CC3EBB21DDEBA29E2E38F9D9 :



      1 #!perl6
      2
      3 use v6;
      4
      5 unit module Sparrow6:ver<0.0.1>;
      6 use File::Directory::Tree;
      7 use Hash::Merge;
      8 use YAMLish;
      9
     10 class Runner {
     11
     12   has Str $.root;
     13   has Str $.sparrow-root;
     14   has Bool $.debug;
     15   has Hash $.parameters;
     16   has Hash $.task-config is rw;
     17
     18   method !cache-root-dir {
     19
     20     my $cache-root-dir = $.sparrow-root       ??
     21     $.sparrow-root ~ "/tmp/" ~ $*PID          !!
     22     %*ENV<HOME> ~ "/.sparrow6/tmp/" ~ $*PID;
     23
     24   }
     25
     26   method task-run() {
     27
     28     if self!cache-root-dir.IO ~~ :e {
     29       empty-directory self!cache-root-dir
     30     }
     31
     32     if "{$.root}/suite.yaml".IO ~~ :e {
     33       self!log("load plugin configuration","{$.root}/suite.yaml");
     34       my $plugin-config = load-yaml(slurp "{$.root}/suite.yaml");
     35       self!log("parse plugin configuration",$plugin-config.perl);
     36       self!log("input parameters",$.parameters.perl);
     37       $.task-config = %( foo => 100 );
     38       merge-hash $plugin-config, $.parameters;
     39       self!log("merged task config",$.task-config.perl);