[nqp]: Add 'unless' statement.

src/NQP/Actions.pm

@@ -63,6 +63,12 @@ method statement_control:sym<if>($/) {
     make $past;
 }
 
+method statement_control:sym<unless>($/) {
+    my $past := $<xblock>.ast;
+    $past.pasttype('unless');
+    make $past;
+}
+
 ## Terms
 
 method term:sym<identifier>($/) {

src/NQP/Grammar.pm

@@ -60,6 +60,12 @@ token statement_control:sym<if> {
     [ 'else'\s <else=pblock> ]?
 }
 
+token statement_control:sym<unless> {
+    $<sym>=['unless'] :s
+    <xblock>
+    [ <!before 'else'> || <.panic: 'unless does not take "else", please rewrite using "if"'> ]
+}
+
 ## Terms
 
 proto token term { <...> }

t/nqp/03-unless.t

@@ -0,0 +1,18 @@
+#!./parrot nqp.pbc
+
+# check control structure 'unless'
+
+say('1..4');
+
+unless 0 { say("ok 1 # on one line"); }
+
+say("ok 2 # statements following unless are okay");
+
+unless 0 {
+    say("ok 3 # multi-line unless");
+}
+
+unless 1 {
+    print("not ");
+}
+say("ok 4 # testing conditional");