implement reference link (first step: currently not resolved)

src/Compiler.pir

@@ -239,6 +239,28 @@ Return generated HTML for all of its children.
     .return (code)
 .end
 
+=item html(Markdown::RefLink node)
+
+=cut
+
+.sub 'html' :method :multi(_,['Markdown';'RefLink'])
+    .param pmc node
+    .local pmc code
+    new code, 'CodeString'
+    $S0 = "<a href=\"\">"
+    $S1 = self.'html_children'(node)
+    if $S1 goto L1
+    $S1 = node.'key'()
+    $I0 = length $S1
+    $I0 -= 2
+    $S1 = substr $S1, 1, $I0
+  L1:
+    $S0 .= $S1
+    $S0 .= "</a>"
+    set code, $S0
+    .return (code)
+.end
+
 =item html(Markdown::Email node)
 
 =cut

src/Node.pir

@@ -30,6 +30,7 @@ for Markdown.
     p6meta.'new_class'('Markdown::ListItem', 'parent'=>base)
     p6meta.'new_class'('Markdown::OrderedList', 'parent'=>base)
     p6meta.'new_class'('Markdown::Para', 'parent'=>base)
+    p6meta.'new_class'('Markdown::RefLink', 'parent'=>base)
     p6meta.'new_class'('Markdown::Space', 'parent'=>base)
     p6meta.'new_class'('Markdown::Strong', 'parent'=>base)
     p6meta.'new_class'('Markdown::Title', 'parent'=>base)
@@ -59,6 +60,15 @@ for Markdown.
 .end
 
 
+.namespace [ 'Markdown';'RefLink' ]
+
+.sub 'key' :method
+    .param pmc value           :optional
+    .param int has_value       :opt_flag
+    .tailcall self.'attr'('key', value, has_value)
+.end
+
+
 .namespace [ 'Markdown';'Title' ]
 
 .sub 'level' :method

src/parser/actions.pm

@@ -216,6 +216,22 @@ method Link($/, $key) {
     make $( $/{$key} );
 }
 
+method ReferenceLink($/, $key) {
+    make $( $/{$key} );
+}
+
+method ReferenceLinkDouble($/) {
+    my $mast := Markdown::RefLink.new( :key( ~$<Label>[1].text() ) );
+    for $<Label>[0]<Inline> {
+        $mast.push( $( $_ ) );
+    }
+    make $mast;
+}
+
+method ReferenceLinkSingle($/) {
+    make Markdown::RefLink.new( :key( ~$<Label>.text() ) );
+}
+
 method ExplicitLink($/) {
     my $mast := Markdown::Link.new( :title( ~$<Title>.text() ),
                                     :url( ~$<Source><SourceContents>.text() ) );

src/parser/grammar.pg

@@ -292,6 +292,24 @@ token StrongUI {
 token Link {
     | <AutoLink> {*}            #= AutoLink
     | <ExplicitLink> {*}        #= ExplicitLink
+    | <ReferenceLink> {*}       #= ReferenceLink
+}
+
+token ReferenceLink {
+    | <ReferenceLinkDouble> {*} #= ReferenceLinkDouble
+    | <ReferenceLinkSingle> {*} #= ReferenceLinkSingle
+}
+
+token _EmptyLabel { '[]' }
+
+token ReferenceLinkDouble {
+    <Label> <.Spnl> <!_EmptyLabel> <Label>
+    {*}
+}
+
+token ReferenceLinkSingle {
+    <Label> [ <.Spnl> <._EmptyLabel> ]?
+    {*}
 }
 
 token ExplicitLink {