diff --git a/lib/Minilisp.pm b/lib/Minilisp.pm
index 2e575c2..57bbe83 100644
--- a/lib/Minilisp.pm
+++ b/lib/Minilisp.pm
@@ -102,6 +102,9 @@ my %stdctx = (
     print "$e\n";
     return undef;
   },
+  'null' => sub { my ($a) = @_; return ! defined $a; },
+  'evenp' => sub { my ($a) = @_; return ($a % 2 == 0); },
+  'oddp' => sub { my ($a) = @_; return ($a % 2 != 0); },
   'eq' => sub { my ($a, $b) = @_; return ($a eq $b); },
   'ne' => sub { my ($a, $b) = @_; return ($a ne $b); },
   '==' => sub { my ($a, $b) = @_; return ($a == $b); },