Great, redefinition of truth works as expected! I added a test to S04-declarations/constant.t with the following commit: https://github.com/perl6/roast/commit/c855d94be4
[perl #111734] [BUG] Can't locally redefine True in Rakudo
Christian Bartolomaeus via RT Tue, 14 Oct 2014 01:32:54 -0700