Refactor Writer Interface

The existing approach made it hard to extend existing writers.
With this change, replacing individual methods of a writer is possible by
embedding it.

Sharing the WriteNodes function also removes some unnecesseray duplication, so
win win.

org/document.go

@@ -41,14 +41,6 @@ type Document struct {
 	Error          error
 }
 
-// Writer is the interface that is used to export a parsed document into a new format. See Document.Write().
-type Writer interface {
-	Before(*Document)   // Before is called before any nodes are passed to the writer.
-	After(*Document)    // After is called after all nodes have been passed to the writer.
-	WriteNodes(...Node) // WriteNodes is called with the nodes of the parsed document.
-	String() string     // String is called at the very end to retrieve the final output.
-}
-
 // Node represents a parsed node of the document. It's an empty interface and can be ignored.
 type Node interface{}
 
@@ -105,7 +97,7 @@ func (d *Document) Write(w Writer) (out string, err error) {
 		return "", fmt.Errorf("could not write output: parse was not called")
 	}
 	w.Before(d)
-	w.WriteNodes(d.Nodes...)
+	WriteNodes(w, d.Nodes...)
 	w.After(d)
 	return w.String(), err
 }

org/html_writer.go

@@ -63,87 +63,29 @@ func (w *HTMLWriter) emptyClone() *HTMLWriter {
 
 func (w *HTMLWriter) nodesAsString(nodes ...Node) string {
 	tmp := w.emptyClone()
-	tmp.WriteNodes(nodes...)
+	WriteNodes(tmp, nodes...)
 	return tmp.String()
 }
 
 func (w *HTMLWriter) Before(d *Document) {
 	w.document = d
 	w.log = d.Log
-	w.writeOutline(d)
+	w.WriteOutline(d)
 }
 
 func (w *HTMLWriter) After(d *Document) {
-	w.writeFootnotes(d)
+	w.WriteFootnotes(d)
 }
 
-func (w *HTMLWriter) WriteNodes(ns ...Node) {
+func (w *HTMLWriter) WriteComment(Comment)               {}
-	for _, n := range ns {
+func (w *HTMLWriter) WritePropertyDrawer(PropertyDrawer) {}
-		switch n := n.(type) {
-		case Keyword:
-			w.writeKeyword(n)
-		case Include:
-			w.writeInclude(n)
-		case Comment:
-			continue
-		case NodeWithMeta:
-			w.writeNodeWithMeta(n)
-		case Headline:
-			w.writeHeadline(n)
-		case Block:
-			w.writeBlock(n)
-		case Drawer:
-			w.writeDrawer(n)
-		case PropertyDrawer:
-			continue
 
-		case FootnoteDefinition:
+func (w *HTMLWriter) WriteBlock(b Block) {
-			continue
-
-		case List:
-			w.writeList(n)
-		case ListItem:
-			w.writeListItem(n)
-		case DescriptiveListItem:
-			w.writeDescriptiveListItem(n)
-
-		case Table:
-			w.writeTable(n)
-
-		case Paragraph:
-			w.writeParagraph(n)
-		case Example:
-			w.writeExample(n)
-		case HorizontalRule:
-			w.writeHorizontalRule(n)
-		case Text:
-			w.writeText(n)
-		case Emphasis:
-			w.writeEmphasis(n)
-		case StatisticToken:
-			w.writeStatisticToken(n)
-		case ExplicitLineBreak:
-			w.writeExplicitLineBreak(n)
-		case LineBreak:
-			w.writeLineBreak(n)
-		case RegularLink:
-			w.writeRegularLink(n)
-		case FootnoteLink:
-			w.writeFootnoteLink(n)
-		default:
-			if n != nil {
-				panic(fmt.Sprintf("bad node %#v", n))
-			}
-		}
-	}
-}
-
-func (w *HTMLWriter) writeBlock(b Block) {
 	content := ""
 	if isRawTextBlock(b.Name) {
 		exportWriter := w.emptyClone()
 		exportWriter.htmlEscape = false
-		exportWriter.WriteNodes(b.Children...)
+		WriteNodes(exportWriter, b.Children...)
 		content = strings.TrimRightFunc(exportWriter.String(), unicode.IsSpace)
 	} else {
 		content = w.nodesAsString(b.Children...)
@@ -170,30 +112,32 @@ func (w *HTMLWriter) writeBlock(b Block) {
 	}
 }
 
-func (w *HTMLWriter) writeDrawer(d Drawer) {
+func (w *HTMLWriter) WriteDrawer(d Drawer) {
-	w.WriteNodes(d.Children...)
+	WriteNodes(w, d.Children...)
 }
 
-func (w *HTMLWriter) writeKeyword(k Keyword) {
+func (w *HTMLWriter) WriteKeyword(k Keyword) {
 	if k.Key == "HTML" {
 		w.WriteString(k.Value + "\n")
 	}
 }
 
-func (w *HTMLWriter) writeInclude(i Include) {
+func (w *HTMLWriter) WriteInclude(i Include) {
-	w.WriteNodes(i.Resolve())
+	WriteNodes(w, i.Resolve())
 }
 
+func (w *HTMLWriter) WriteFootnoteDefinition(FootnoteDefinition) {}
+
 func (w *HTMLWriter) writeFootnoteDefinition(f FootnoteDefinition) {
 	n := f.Name
 	w.WriteString(`<div class="footnote-definition">` + "\n")
 	w.WriteString(fmt.Sprintf(`<sup id="footnote-%s"><a href="#footnote-reference-%s">%s</a></sup>`, n, n, n) + "\n")
 	w.WriteString(`<div class="footnote-body">` + "\n")
-	w.WriteNodes(f.Children...)
+	WriteNodes(w, f.Children...)
 	w.WriteString("</div>\n</div>\n")
 }
 
-func (w *HTMLWriter) writeFootnotes(d *Document) {
+func (w *HTMLWriter) WriteFootnotes(d *Document) {
 	if !w.document.GetOption("f") || len(d.Footnotes.Definitions) == 0 {
 		return
 	}
@@ -206,7 +150,7 @@ func (w *HTMLWriter) writeFootnotes(d *Document) {
 	w.WriteString("</div>\n</div>\n")
 }
 
-func (w *HTMLWriter) writeOutline(d *Document) {
+func (w *HTMLWriter) WriteOutline(d *Document) {
 	if w.document.GetOption("toc") && len(d.Outline.Children) != 0 {
 		w.WriteString("<nav>\n<ul>\n")
 		for _, section := range d.Outline.Children {
@@ -232,7 +176,7 @@ func (w *HTMLWriter) writeSection(section *Section) {
 	w.WriteString("</li>\n")
 }
 
-func (w *HTMLWriter) writeHeadline(h Headline) {
+func (w *HTMLWriter) WriteHeadline(h Headline) {
 	for _, excludeTag := range strings.Fields(w.document.Get("EXCLUDE_TAGS")) {
 		for _, tag := range h.Tags {
 			if excludeTag == tag {
@@ -249,7 +193,7 @@ func (w *HTMLWriter) writeHeadline(h Headline) {
 		w.WriteString(fmt.Sprintf(`<span class="priority">[%s]</span>`, h.Priority) + "\n")
 	}
 
-	w.WriteNodes(h.Title...)
+	WriteNodes(w, h.Title...)
 	if w.document.GetOption("tags") && len(h.Tags) != 0 {
 		tags := make([]string, len(h.Tags))
 		for i, tag := range h.Tags {
@@ -259,10 +203,10 @@ func (w *HTMLWriter) writeHeadline(h Headline) {
 		w.WriteString(fmt.Sprintf(`<span class="tags">%s</span>`, strings.Join(tags, "&#xa0;")))
 	}
 	w.WriteString(fmt.Sprintf("\n</h%d>\n", h.Lvl))
-	w.WriteNodes(h.Children...)
+	WriteNodes(w, h.Children...)
 }
 
-func (w *HTMLWriter) writeText(t Text) {
+func (w *HTMLWriter) WriteText(t Text) {
 	if !w.htmlEscape {
 		w.WriteString(t.Content)
 	} else if !w.document.GetOption("e") || t.IsRaw {
@@ -272,29 +216,29 @@ func (w *HTMLWriter) writeText(t Text) {
 	}
 }
 
-func (w *HTMLWriter) writeEmphasis(e Emphasis) {
+func (w *HTMLWriter) WriteEmphasis(e Emphasis) {
 	tags, ok := emphasisTags[e.Kind]
 	if !ok {
 		panic(fmt.Sprintf("bad emphasis %#v", e))
 	}
 	w.WriteString(tags[0])
-	w.WriteNodes(e.Content...)
+	WriteNodes(w, e.Content...)
 	w.WriteString(tags[1])
 }
 
-func (w *HTMLWriter) writeStatisticToken(s StatisticToken) {
+func (w *HTMLWriter) WriteStatisticToken(s StatisticToken) {
 	w.WriteString(fmt.Sprintf(`<code class="statistic">[%s]</code>`, s.Content))
 }
 
-func (w *HTMLWriter) writeLineBreak(l LineBreak) {
+func (w *HTMLWriter) WriteLineBreak(l LineBreak) {
 	w.WriteString(strings.Repeat("\n", l.Count))
 }
 
-func (w *HTMLWriter) writeExplicitLineBreak(l ExplicitLineBreak) {
+func (w *HTMLWriter) WriteExplicitLineBreak(l ExplicitLineBreak) {
 	w.WriteString("<br>\n")
 }
 
-func (w *HTMLWriter) writeFootnoteLink(l FootnoteLink) {
+func (w *HTMLWriter) WriteFootnoteLink(l FootnoteLink) {
 	if !w.document.GetOption("f") {
 		return
 	}
@@ -302,7 +246,7 @@ func (w *HTMLWriter) writeFootnoteLink(l FootnoteLink) {
 	w.WriteString(fmt.Sprintf(`<sup class="footnote-reference"><a id="footnote-reference-%s" href="#footnote-%s">%s</a></sup>`, n, n, n))
 }
 
-func (w *HTMLWriter) writeRegularLink(l RegularLink) {
+func (w *HTMLWriter) WriteRegularLink(l RegularLink) {
 	url := html.EscapeString(l.URL)
 	if l.Protocol == "file" {
 		url = url[len("file:"):]
@@ -321,27 +265,27 @@ func (w *HTMLWriter) writeRegularLink(l RegularLink) {
 	}
 }
 
-func (w *HTMLWriter) writeList(l List) {
+func (w *HTMLWriter) WriteList(l List) {
 	tags, ok := listTags[l.Kind]
 	if !ok {
 		panic(fmt.Sprintf("bad list kind %#v", l))
 	}
 	w.WriteString(tags[0] + "\n")
-	w.WriteNodes(l.Items...)
+	WriteNodes(w, l.Items...)
 	w.WriteString(tags[1] + "\n")
 }
 
-func (w *HTMLWriter) writeListItem(li ListItem) {
+func (w *HTMLWriter) WriteListItem(li ListItem) {
 	if li.Status != "" {
 		w.WriteString(fmt.Sprintf("<li class=\"%s\">\n", listItemStatuses[li.Status]))
 	} else {
 		w.WriteString("<li>\n")
 	}
-	w.WriteNodes(li.Children...)
+	WriteNodes(w, li.Children...)
 	w.WriteString("</li>\n")
 }
 
-func (w *HTMLWriter) writeDescriptiveListItem(di DescriptiveListItem) {
+func (w *HTMLWriter) WriteDescriptiveListItem(di DescriptiveListItem) {
 	if di.Status != "" {
 		w.WriteString(fmt.Sprintf("<dt class=\"%s\">\n", listItemStatuses[di.Status]))
 	} else {
@@ -349,16 +293,16 @@ func (w *HTMLWriter) writeDescriptiveListItem(di DescriptiveListItem) {
 	}
 
 	if len(di.Term) != 0 {
-		w.WriteNodes(di.Term...)
+		WriteNodes(w, di.Term...)
 	} else {
 		w.WriteString("?")
 	}
 	w.WriteString("<dd>\n")
-	w.WriteNodes(di.Details...)
+	WriteNodes(w, di.Details...)
 	w.WriteString("<dd>\n")
 }
 
-func (w *HTMLWriter) writeParagraph(p Paragraph) {
+func (w *HTMLWriter) WriteParagraph(p Paragraph) {
 	if len(p.Children) == 0 {
 		return
 	}
@@ -366,26 +310,26 @@ func (w *HTMLWriter) writeParagraph(p Paragraph) {
 	if _, ok := p.Children[0].(LineBreak); !ok {
 		w.WriteString("\n")
 	}
-	w.WriteNodes(p.Children...)
+	WriteNodes(w, p.Children...)
 	w.WriteString("\n</p>\n")
 }
 
-func (w *HTMLWriter) writeExample(e Example) {
+func (w *HTMLWriter) WriteExample(e Example) {
 	w.WriteString(`<pre class="example">` + "\n")
 	if len(e.Children) != 0 {
 		for _, n := range e.Children {
-			w.WriteNodes(n)
+			WriteNodes(w, n)
 			w.WriteString("\n")
 		}
 	}
 	w.WriteString("</pre>\n")
 }
 
-func (w *HTMLWriter) writeHorizontalRule(h HorizontalRule) {
+func (w *HTMLWriter) WriteHorizontalRule(h HorizontalRule) {
 	w.WriteString("<hr>\n")
 }
 
-func (w *HTMLWriter) writeNodeWithMeta(n NodeWithMeta) {
+func (w *HTMLWriter) WriteNodeWithMeta(n NodeWithMeta) {
 	out := w.nodesAsString(n.Node)
 	if p, ok := n.Node.(Paragraph); ok {
 		if len(p.Children) == 1 && isImageOrVideoLink(p.Children[0]) {
@@ -408,7 +352,7 @@ func (w *HTMLWriter) writeNodeWithMeta(n NodeWithMeta) {
 	w.WriteString(out)
 }
 
-func (w *HTMLWriter) writeTable(t Table) {
+func (w *HTMLWriter) WriteTable(t Table) {
 	w.WriteString("<table>\n")
 	beforeFirstContentRow := true
 	for i, row := range t.Rows {
@@ -439,7 +383,7 @@ func (w *HTMLWriter) writeTableColumns(columns []Column, tag string) {
 		} else {
 			w.WriteString(fmt.Sprintf(`<%s class="align-%s">`, tag, column.Align))
 		}
-		w.WriteNodes(column.Children...)
+		WriteNodes(w, column.Children...)
 		w.WriteString(fmt.Sprintf("</%s>\n", tag))
 	}
 	w.WriteString("</tr>\n")

org/org_writer.go

@@ -44,72 +44,11 @@ func (w *OrgWriter) emptyClone() *OrgWriter {
 
 func (w *OrgWriter) nodesAsString(nodes ...Node) string {
 	tmp := w.emptyClone()
-	tmp.WriteNodes(nodes...)
+	WriteNodes(tmp, nodes...)
 	return tmp.String()
 }
 
-func (w *OrgWriter) WriteNodes(ns ...Node) {
+func (w *OrgWriter) WriteHeadline(h Headline) {
-	for _, n := range ns {
-		switch n := n.(type) {
-		case Comment:
-			w.writeComment(n)
-		case Keyword:
-			w.writeKeyword(n)
-		case Include:
-			w.writeKeyword(n.Keyword)
-		case NodeWithMeta:
-			w.writeNodeWithMeta(n)
-		case Headline:
-			w.writeHeadline(n)
-		case Block:
-			w.writeBlock(n)
-		case Drawer:
-			w.writeDrawer(n)
-		case PropertyDrawer:
-			w.writePropertyDrawer(n)
-
-		case FootnoteDefinition:
-			w.writeFootnoteDefinition(n)
-
-		case List:
-			w.writeList(n)
-		case ListItem:
-			w.writeListItem(n)
-		case DescriptiveListItem:
-			w.writeDescriptiveListItem(n)
-
-		case Table:
-			w.writeTable(n)
-
-		case Paragraph:
-			w.writeParagraph(n)
-		case Example:
-			w.writeExample(n)
-		case HorizontalRule:
-			w.writeHorizontalRule(n)
-		case Text:
-			w.writeText(n)
-		case Emphasis:
-			w.writeEmphasis(n)
-		case StatisticToken:
-			w.writeStatisticToken(n)
-		case LineBreak:
-			w.writeLineBreak(n)
-		case ExplicitLineBreak:
-			w.writeExplicitLineBreak(n)
-		case RegularLink:
-			w.writeRegularLink(n)
-		case FootnoteLink:
-			w.writeFootnoteLink(n)
-		default:
-			if n != nil {
-				panic(fmt.Sprintf("bad node %#v", n))
-			}
-		}
-	}
-}
-
-func (w *OrgWriter) writeHeadline(h Headline) {
 	tmp := w.emptyClone()
 	tmp.WriteString(strings.Repeat("*", h.Lvl))
 	if h.Status != "" {
@@ -119,7 +58,7 @@ func (w *OrgWriter) writeHeadline(h Headline) {
 		tmp.WriteString(" [#" + h.Priority + "]")
 	}
 	tmp.WriteString(" ")
-	tmp.WriteNodes(h.Title...)
+	WriteNodes(tmp, h.Title...)
 	hString := tmp.String()
 	if len(h.Tags) != 0 {
 		tString := ":" + strings.Join(h.Tags, ":") + ":"
@@ -136,12 +75,12 @@ func (w *OrgWriter) writeHeadline(h Headline) {
 		w.WriteString(w.indent)
 	}
 	if h.Properties != nil {
-		w.WriteNodes(*h.Properties)
+		WriteNodes(w, *h.Properties)
 	}
-	w.WriteNodes(h.Children...)
+	WriteNodes(w, h.Children...)
 }
 
-func (w *OrgWriter) writeBlock(b Block) {
+func (w *OrgWriter) WriteBlock(b Block) {
 	w.WriteString(w.indent + "#+BEGIN_" + b.Name)
 	if len(b.Parameters) != 0 {
 		w.WriteString(" " + strings.Join(b.Parameters, " "))
@@ -150,20 +89,20 @@ func (w *OrgWriter) writeBlock(b Block) {
 	if isRawTextBlock(b.Name) {
 		w.WriteString(w.indent)
 	}
-	w.WriteNodes(b.Children...)
+	WriteNodes(w, b.Children...)
 	if !isRawTextBlock(b.Name) {
 		w.WriteString(w.indent)
 	}
 	w.WriteString("#+END_" + b.Name + "\n")
 }
 
-func (w *OrgWriter) writeDrawer(d Drawer) {
+func (w *OrgWriter) WriteDrawer(d Drawer) {
 	w.WriteString(w.indent + ":" + d.Name + ":\n")
-	w.WriteNodes(d.Children...)
+	WriteNodes(w, d.Children...)
 	w.WriteString(w.indent + ":END:\n")
 }
 
-func (w *OrgWriter) writePropertyDrawer(d PropertyDrawer) {
+func (w *OrgWriter) WritePropertyDrawer(d PropertyDrawer) {
 	w.WriteString(":PROPERTIES:\n")
 	for _, kvPair := range d.Properties {
 		k, v := kvPair[0], kvPair[1]
@@ -175,7 +114,7 @@ func (w *OrgWriter) writePropertyDrawer(d PropertyDrawer) {
 	w.WriteString(":END:\n")
 }
 
-func (w *OrgWriter) writeFootnoteDefinition(f FootnoteDefinition) {
+func (w *OrgWriter) WriteFootnoteDefinition(f FootnoteDefinition) {
 	w.WriteString(fmt.Sprintf("[fn:%s]", f.Name))
 	content := w.nodesAsString(f.Children...)
 	if content != "" && !unicode.IsSpace(rune(content[0])) {
@@ -184,7 +123,7 @@ func (w *OrgWriter) writeFootnoteDefinition(f FootnoteDefinition) {
 	w.WriteString(content)
 }
 
-func (w *OrgWriter) writeParagraph(p Paragraph) {
+func (w *OrgWriter) WriteParagraph(p Paragraph) {
 	content := w.nodesAsString(p.Children...)
 	if len(content) > 0 && content[0] != '\n' {
 		w.WriteString(w.indent)
@@ -192,7 +131,7 @@ func (w *OrgWriter) writeParagraph(p Paragraph) {
 	w.WriteString(content + "\n")
 }
 
-func (w *OrgWriter) writeExample(e Example) {
+func (w *OrgWriter) WriteExample(e Example) {
 	for _, n := range e.Children {
 		w.WriteString(w.indent + ":")
 		if content := w.nodesAsString(n); content != "" {
@@ -202,7 +141,7 @@ func (w *OrgWriter) writeExample(e Example) {
 	}
 }
 
-func (w *OrgWriter) writeKeyword(k Keyword) {
+func (w *OrgWriter) WriteKeyword(k Keyword) {
 	w.WriteString(w.indent + "#+" + k.Key + ":")
 	if k.Value != "" {
 		w.WriteString(" " + k.Value)
@@ -210,29 +149,33 @@ func (w *OrgWriter) writeKeyword(k Keyword) {
 	w.WriteString("\n")
 }
 
-func (w *OrgWriter) writeNodeWithMeta(n NodeWithMeta) {
+func (w *OrgWriter) WriteInclude(i Include) {
+	w.WriteKeyword(i.Keyword)
+}
+
+func (w *OrgWriter) WriteNodeWithMeta(n NodeWithMeta) {
 	for _, ns := range n.Meta.Caption {
 		w.WriteString("#+CAPTION: ")
-		w.WriteNodes(ns...)
+		WriteNodes(w, ns...)
 		w.WriteString("\n")
 	}
 	for _, attributes := range n.Meta.HTMLAttributes {
 		w.WriteString("#+ATTR_HTML: ")
 		w.WriteString(strings.Join(attributes, " ") + "\n")
 	}
-	w.WriteNodes(n.Node)
+	WriteNodes(w, n.Node)
 }
 
-func (w *OrgWriter) writeComment(c Comment) {
+func (w *OrgWriter) WriteComment(c Comment) {
 	w.WriteString(w.indent + "#" + c.Content + "\n")
 }
 
-func (w *OrgWriter) writeList(l List) { w.WriteNodes(l.Items...) }
+func (w *OrgWriter) WriteList(l List) { WriteNodes(w, l.Items...) }
 
-func (w *OrgWriter) writeListItem(li ListItem) {
+func (w *OrgWriter) WriteListItem(li ListItem) {
 	liWriter := w.emptyClone()
 	liWriter.indent = w.indent + strings.Repeat(" ", len(li.Bullet)+1)
-	liWriter.WriteNodes(li.Children...)
+	WriteNodes(liWriter, li.Children...)
 	content := strings.TrimPrefix(liWriter.String(), liWriter.indent)
 	w.WriteString(w.indent + li.Bullet)
 	if li.Status != "" {
@@ -245,7 +188,7 @@ func (w *OrgWriter) writeListItem(li ListItem) {
 	}
 }
 
-func (w *OrgWriter) writeDescriptiveListItem(di DescriptiveListItem) {
+func (w *OrgWriter) WriteDescriptiveListItem(di DescriptiveListItem) {
 	w.WriteString(w.indent + di.Bullet)
 	if di.Status != "" {
 		w.WriteString(fmt.Sprintf(" [%s]", di.Status))
@@ -258,7 +201,7 @@ func (w *OrgWriter) writeDescriptiveListItem(di DescriptiveListItem) {
 	}
 	diWriter := w.emptyClone()
 	diWriter.indent = indent
-	diWriter.WriteNodes(di.Details...)
+	WriteNodes(diWriter, di.Details...)
 	details := strings.TrimPrefix(diWriter.String(), diWriter.indent)
 	if len(details) > 0 && details[0] == '\n' {
 		w.WriteString(details)
@@ -267,7 +210,7 @@ func (w *OrgWriter) writeDescriptiveListItem(di DescriptiveListItem) {
 	}
 }
 
-func (w *OrgWriter) writeTable(t Table) {
+func (w *OrgWriter) WriteTable(t Table) {
 	for _, row := range t.Rows {
 		w.WriteString(w.indent)
 		if len(row.Columns) == 0 {
@@ -309,51 +252,51 @@ func (w *OrgWriter) writeTable(t Table) {
 	}
 }
 
-func (w *OrgWriter) writeHorizontalRule(hr HorizontalRule) {
+func (w *OrgWriter) WriteHorizontalRule(hr HorizontalRule) {
 	w.WriteString(w.indent + "-----\n")
 }
 
-func (w *OrgWriter) writeText(t Text) { w.WriteString(t.Content) }
+func (w *OrgWriter) WriteText(t Text) { w.WriteString(t.Content) }
 
-func (w *OrgWriter) writeEmphasis(e Emphasis) {
+func (w *OrgWriter) WriteEmphasis(e Emphasis) {
 	borders, ok := emphasisOrgBorders[e.Kind]
 	if !ok {
 		panic(fmt.Sprintf("bad emphasis %#v", e))
 	}
 	w.WriteString(borders[0])
-	w.WriteNodes(e.Content...)
+	WriteNodes(w, e.Content...)
 	w.WriteString(borders[1])
 }
 
-func (w *OrgWriter) writeStatisticToken(s StatisticToken) {
+func (w *OrgWriter) WriteStatisticToken(s StatisticToken) {
 	w.WriteString(fmt.Sprintf("[%s]", s.Content))
 }
 
-func (w *OrgWriter) writeLineBreak(l LineBreak) {
+func (w *OrgWriter) WriteLineBreak(l LineBreak) {
 	w.WriteString(strings.Repeat("\n"+w.indent, l.Count))
 }
 
-func (w *OrgWriter) writeExplicitLineBreak(l ExplicitLineBreak) {
+func (w *OrgWriter) WriteExplicitLineBreak(l ExplicitLineBreak) {
 	w.WriteString(`\\` + "\n" + w.indent)
 }
 
-func (w *OrgWriter) writeFootnoteLink(l FootnoteLink) {
+func (w *OrgWriter) WriteFootnoteLink(l FootnoteLink) {
 	w.WriteString("[fn:" + l.Name)
 	if l.Definition != nil {
 		w.WriteString(":")
-		w.WriteNodes(l.Definition.Children[0].(Paragraph).Children...)
+		WriteNodes(w, l.Definition.Children[0].(Paragraph).Children...)
 	}
 	w.WriteString("]")
 }
 
-func (w *OrgWriter) writeRegularLink(l RegularLink) {
+func (w *OrgWriter) WriteRegularLink(l RegularLink) {
 	if l.AutoLink {
 		w.WriteString(l.URL)
 	} else if l.Description == nil {
 		w.WriteString(fmt.Sprintf("[[%s]]", l.URL))
 	} else {
 		descriptionWriter := w.emptyClone()
-		descriptionWriter.WriteNodes(l.Description...)
+		WriteNodes(descriptionWriter, l.Description...)
 		description := descriptionWriter.String()
 		w.WriteString(fmt.Sprintf("[[%s][%s]]", l.URL, description))
 	}

org/writer.go

@@ -0,0 +1,91 @@
+package org
+
+import "fmt"
+
+// Writer is the interface that is used to export a parsed document into a new format. See Document.Write().
+type Writer interface {
+	Before(*Document) // Before is called before any nodes are passed to the writer.
+	After(*Document)  // After is called after all nodes have been passed to the writer.
+	String() string   // String is called at the very end to retrieve the final output.
+
+	WriteKeyword(Keyword)
+	WriteInclude(Include)
+	WriteComment(Comment)
+	WriteNodeWithMeta(NodeWithMeta)
+	WriteHeadline(Headline)
+	WriteBlock(Block)
+	WriteExample(Example)
+	WriteDrawer(Drawer)
+	WritePropertyDrawer(PropertyDrawer)
+	WriteList(List)
+	WriteListItem(ListItem)
+	WriteDescriptiveListItem(DescriptiveListItem)
+	WriteTable(Table)
+	WriteHorizontalRule(HorizontalRule)
+	WriteParagraph(Paragraph)
+	WriteText(Text)
+	WriteEmphasis(Emphasis)
+	WriteStatisticToken(StatisticToken)
+	WriteExplicitLineBreak(ExplicitLineBreak)
+	WriteLineBreak(LineBreak)
+	WriteRegularLink(RegularLink)
+	WriteFootnoteLink(FootnoteLink)
+	WriteFootnoteDefinition(FootnoteDefinition)
+}
+
+func WriteNodes(w Writer, nodes ...Node) {
+	for _, n := range nodes {
+		switch n := n.(type) {
+		case Keyword:
+			w.WriteKeyword(n)
+		case Include:
+			w.WriteInclude(n)
+		case Comment:
+			w.WriteComment(n)
+		case NodeWithMeta:
+			w.WriteNodeWithMeta(n)
+		case Headline:
+			w.WriteHeadline(n)
+		case Block:
+			w.WriteBlock(n)
+		case Example:
+			w.WriteExample(n)
+		case Drawer:
+			w.WriteDrawer(n)
+		case PropertyDrawer:
+			w.WritePropertyDrawer(n)
+		case List:
+			w.WriteList(n)
+		case ListItem:
+			w.WriteListItem(n)
+		case DescriptiveListItem:
+			w.WriteDescriptiveListItem(n)
+		case Table:
+			w.WriteTable(n)
+		case HorizontalRule:
+			w.WriteHorizontalRule(n)
+		case Paragraph:
+			w.WriteParagraph(n)
+		case Text:
+			w.WriteText(n)
+		case Emphasis:
+			w.WriteEmphasis(n)
+		case StatisticToken:
+			w.WriteStatisticToken(n)
+		case ExplicitLineBreak:
+			w.WriteExplicitLineBreak(n)
+		case LineBreak:
+			w.WriteLineBreak(n)
+		case RegularLink:
+			w.WriteRegularLink(n)
+		case FootnoteLink:
+			w.WriteFootnoteLink(n)
+		case FootnoteDefinition:
+			w.WriteFootnoteDefinition(n)
+		default:
+			if n != nil {
+				panic(fmt.Sprintf("bad node %#v", n))
+			}
+		}
+	}
+}