html: store the current insertion mode in the parser

Currently, the state transition functions in the HTML parser
return the next insertion mode and whether the token is consumed.
This works well except for when one insertion mode needs to use
the rules for another insertion mode. Then the useTheRulesFor
function needs to patch things up. This requires comparing functions
for equality, which is going to stop working.

Adding a field to the parser structure to store the current
insertion mode eliminates the need for useTheRulesFor;
one insertion mode function can now just call the other
directly. The insertion mode will be changed only if it needs to be.

This CL is an alternative to CL 5372078.

R=nigeltao, rsc
CC=golang-dev
https://golang.org/cl/5372079

src/pkg/html/parse.go

@@ -29,6 +29,8 @@ type parser struct {
 	head, form *Node
 	// Other parsing state flags (section 11.2.3.5).
 	scripting, framesetOK bool
+	// im is the current insertion mode.
+	im insertionMode
 	// originalIM is the insertion mode to go back to after completing a text
 	// or inTableText insertion mode.
 	originalIM insertionMode
@@ -265,37 +267,22 @@ func (p *parser) acknowledgeSelfClosingTag() {
 
 // An insertion mode (section 11.2.3.1) is the state transition function from
 // a particular state in the HTML5 parser's state machine. It updates the
-// parser's fields depending on parser.token (where ErrorToken means EOF). In
-// addition to returning the next insertionMode state, it also returns whether
-// the token was consumed.
-type insertionMode func(*parser) (insertionMode, bool)
-
-// useTheRulesFor runs the delegate insertionMode over p, returning the actual
-// insertionMode unless the delegate caused a state transition.
-// Section 11.2.3.1, "using the rules for".
-func useTheRulesFor(p *parser, actual, delegate insertionMode) (insertionMode, bool) {
-	im, consumed := delegate(p)
-	if p.originalIM == delegate {
-		p.originalIM = actual
-	}
-	if im != delegate {
-		return im, consumed
-	}
-	return actual, consumed
-}
+// parser's fields depending on parser.tok (where ErrorToken means EOF).
+// It returns whether the token was consumed.
+type insertionMode func(*parser) bool
 
 // setOriginalIM sets the insertion mode to return to after completing a text or
 // inTableText insertion mode.
 // Section 11.2.3.1, "using the rules for".
-func (p *parser) setOriginalIM(im insertionMode) {
+func (p *parser) setOriginalIM() {
 	if p.originalIM != nil {
 		panic("html: bad parser state: originalIM was set twice")
 	}
-	p.originalIM = im
+	p.originalIM = p.im
 }
 
 // Section 11.2.3.1, "reset the insertion mode".
-func (p *parser) resetInsertionMode() insertionMode {
+func (p *parser) resetInsertionMode() {
 	for i := len(p.oe) - 1; i >= 0; i-- {
 		n := p.oe[i]
 		if i == 0 {
@@ -303,60 +290,66 @@ func (p *parser) resetInsertionMode() insertionMode {
 		}
 		switch n.Data {
 		case "select":
-			return inSelectIM
+			p.im = inSelectIM
 		case "td", "th":
-			return inCellIM
+			p.im = inCellIM
 		case "tr":
-			return inRowIM
+			p.im = inRowIM
 		case "tbody", "thead", "tfoot":
-			return inTableBodyIM
+			p.im = inTableBodyIM
 		case "caption":
-			// TODO: return inCaptionIM
+			// TODO: p.im = inCaptionIM
 		case "colgroup":
-			return inColumnGroupIM
+			p.im = inColumnGroupIM
 		case "table":
-			return inTableIM
+			p.im = inTableIM
 		case "head":
-			return inBodyIM
+			p.im = inBodyIM
 		case "body":
-			return inBodyIM
+			p.im = inBodyIM
 		case "frameset":
-			return inFramesetIM
+			p.im = inFramesetIM
 		case "html":
-			return beforeHeadIM
+			p.im = beforeHeadIM
+		default:
+			continue
 		}
+		return
 	}
-	return inBodyIM
+	p.im = inBodyIM
 }
 
 // Section 11.2.5.4.1.
-func initialIM(p *parser) (insertionMode, bool) {
+func initialIM(p *parser) bool {
 	switch p.tok.Type {
 	case CommentToken:
 		p.doc.Add(&Node{
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return initialIM, true
+		return true
 	case DoctypeToken:
 		p.doc.Add(&Node{
 			Type: DoctypeNode,
 			Data: p.tok.Data,
 		})
-		return beforeHTMLIM, true
+		p.im = beforeHTMLIM
+		return true
 	}
 	// TODO: set "quirks mode"? It's defined in the DOM spec instead of HTML5 proper,
 	// and so switching on "quirks mode" might belong in a different package.
-	return beforeHTMLIM, false
+	p.im = beforeHTMLIM
+	return false
 }
 
 // Section 11.2.5.4.2.
-func beforeHTMLIM(p *parser) (insertionMode, bool) {
+func beforeHTMLIM(p *parser) bool {
 	switch p.tok.Type {
 	case StartTagToken:
 		if p.tok.Data == "html" {
 			p.addElement(p.tok.Data, p.tok.Attr)
-			return beforeHeadIM, true
+			p.im = beforeHeadIM
+			return true
 		}
 	case EndTagToken:
 		switch p.tok.Data {
@@ -364,22 +357,23 @@ func beforeHTMLIM(p *parser) (insertionMode, bool) {
 			// Drop down to creating an implied <html> tag.
 		default:
 			// Ignore the token.
-			return beforeHTMLIM, true
+			return true
 		}
 	case CommentToken:
 		p.doc.Add(&Node{
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return beforeHTMLIM, true
+		return true
 	}
 	// Create an implied <html> tag.
 	p.addElement("html", nil)
-	return beforeHeadIM, false
+	p.im = beforeHeadIM
+	return false
 }
 
 // Section 11.2.5.4.3.
-func beforeHeadIM(p *parser) (insertionMode, bool) {
+func beforeHeadIM(p *parser) bool {
 	var (
 		add     bool
 		attr    []Attribute
@@ -397,7 +391,7 @@ func beforeHeadIM(p *parser) (insertionMode, bool) {
 			add = true
 			attr = p.tok.Attr
 		case "html":
-			return useTheRulesFor(p, beforeHeadIM, inBodyIM)
+			return inBodyIM(p)
 		default:
 			implied = true
 		}
@@ -413,19 +407,20 @@ func beforeHeadIM(p *parser) (insertionMode, bool) {
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return beforeHeadIM, true
+		return true
 	}
 	if add || implied {
 		p.addElement("head", attr)
 		p.head = p.top()
 	}
-	return inHeadIM, !implied
+	p.im = inHeadIM
+	return !implied
 }
 
 const whitespace = " \t\r\n\f"
 
 // Section 11.2.5.4.4.
-func inHeadIM(p *parser) (insertionMode, bool) {
+func inHeadIM(p *parser) bool {
 	var (
 		pop     bool
 		implied bool
@@ -439,7 +434,7 @@ func inHeadIM(p *parser) (insertionMode, bool) {
 			// Add the initial whitespace to the current node.
 			p.addText(p.tok.Data[:len(p.tok.Data)-len(s)])
 			if s == "" {
-				return inHeadIM, true
+				return true
 			}
 			p.tok.Data = s
 		}
@@ -452,8 +447,9 @@ func inHeadIM(p *parser) (insertionMode, bool) {
 			p.acknowledgeSelfClosingTag()
 		case "script", "title", "noscript", "noframes", "style":
 			p.addElement(p.tok.Data, p.tok.Attr)
-			p.setOriginalIM(inHeadIM)
-			return textIM, true
+			p.setOriginalIM()
+			p.im = textIM
+			return true
 		default:
 			implied = true
 		}
@@ -465,27 +461,28 @@ func inHeadIM(p *parser) (insertionMode, bool) {
 			implied = true
 		default:
 			// Ignore the token.
-			return inHeadIM, true
+			return true
 		}
 	case CommentToken:
 		p.addChild(&Node{
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return inHeadIM, true
+		return true
 	}
 	if pop || implied {
 		n := p.oe.pop()
 		if n.Data != "head" {
 			panic("html: bad parser state: <head> element not found, in the in-head insertion mode")
 		}
-		return afterHeadIM, !implied
+		p.im = afterHeadIM
+		return !implied
 	}
-	return inHeadIM, true
+	return true
 }
 
 // Section 11.2.5.4.6.
-func afterHeadIM(p *parser) (insertionMode, bool) {
+func afterHeadIM(p *parser) bool {
 	var (
 		add        bool
 		attr       []Attribute
@@ -506,11 +503,12 @@ func afterHeadIM(p *parser) (insertionMode, bool) {
 			framesetOK = false
 		case "frameset":
 			p.addElement(p.tok.Data, p.tok.Attr)
-			return inFramesetIM, true
+			p.im = inFramesetIM
+			return true
 		case "base", "basefont", "bgsound", "link", "meta", "noframes", "script", "style", "title":
 			p.oe = append(p.oe, p.head)
 			defer p.oe.pop()
-			return useTheRulesFor(p, afterHeadIM, inHeadIM)
+			return inHeadIM(p)
 		case "head":
 			// TODO.
 		default:
@@ -524,20 +522,21 @@ func afterHeadIM(p *parser) (insertionMode, bool) {
 			framesetOK = true
 		default:
 			// Ignore the token.
-			return afterHeadIM, true
+			return true
 		}
 	case CommentToken:
 		p.addChild(&Node{
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return afterHeadIM, true
+		return true
 	}
 	if add || implied {
 		p.addElement("body", attr)
 		p.framesetOK = framesetOK
 	}
-	return inBodyIM, !implied
+	p.im = inBodyIM
+	return !implied
 }
 
 // copyAttributes copies attributes of src not found on dst to dst.
@@ -558,7 +557,7 @@ func copyAttributes(dst *Node, src Token) {
 }
 
 // Section 11.2.5.4.7.
-func inBodyIM(p *parser) (insertionMode, bool) {
+func inBodyIM(p *parser) bool {
 	switch p.tok.Type {
 	case TextToken:
 		p.reconstructActiveFormattingElements()
@@ -605,7 +604,8 @@ func inBodyIM(p *parser) (insertionMode, bool) {
 			p.popUntil(buttonScopeStopTags, "p") // TODO: skip this step in quirks mode.
 			p.addElement(p.tok.Data, p.tok.Attr)
 			p.framesetOK = false
-			return inTableIM, true
+			p.im = inTableIM
+			return true
 		case "hr":
 			p.popUntil(buttonScopeStopTags, "p")
 			p.addElement(p.tok.Data, p.tok.Attr)
@@ -617,7 +617,8 @@ func inBodyIM(p *parser) (insertionMode, bool) {
 			p.addElement(p.tok.Data, p.tok.Attr)
 			p.framesetOK = false
 			// TODO: detect <select> inside a table.
-			return inSelectIM, true
+			p.im = inSelectIM
+			return true
 		case "li":
 			p.framesetOK = false
 			for i := len(p.oe) - 1; i >= 0; i-- {
@@ -651,10 +652,10 @@ func inBodyIM(p *parser) (insertionMode, bool) {
 				}
 			}
 		case "base", "basefont", "bgsound", "command", "link", "meta", "noframes", "script", "style", "title":
-			return useTheRulesFor(p, inBodyIM, inHeadIM)
+			return inHeadIM(p)
 		case "image":
 			p.tok.Data = "img"
-			return inBodyIM, false
+			return false
 		case "caption", "col", "colgroup", "frame", "head", "tbody", "td", "tfoot", "th", "thead", "tr":
 			// Ignore the token.
 		default:
@@ -665,7 +666,8 @@ func inBodyIM(p *parser) (insertionMode, bool) {
 		switch p.tok.Data {
 		case "body":
 			// TODO: autoclose the stack of open elements.
-			return afterBodyIM, true
+			p.im = afterBodyIM
+			return true
 		case "p":
 			if !p.elementInScope(buttonScopeStopTags, "p") {
 				p.addElement("p", nil)
@@ -681,7 +683,7 @@ func inBodyIM(p *parser) (insertionMode, bool) {
 			}
 		case "br":
 			p.tok.Type = StartTagToken
-			return inBodyIM, false
+			return false
 		default:
 			p.inBodyEndTagOther(p.tok.Data)
 		}
@@ -692,7 +694,7 @@ func inBodyIM(p *parser) (insertionMode, bool) {
 		})
 	}
 
-	return inBodyIM, true
+	return true
 }
 
 func (p *parser) inBodyEndTagFormatting(tag string) {
@@ -833,27 +835,27 @@ func (p *parser) inBodyEndTagOther(tag string) {
 }
 
 // Section 11.2.5.4.8.
-func textIM(p *parser) (insertionMode, bool) {
+func textIM(p *parser) bool {
 	switch p.tok.Type {
 	case ErrorToken:
 		p.oe.pop()
 	case TextToken:
 		p.addText(p.tok.Data)
-		return textIM, true
+		return true
 	case EndTagToken:
 		p.oe.pop()
 	}
-	o := p.originalIM
+	p.im = p.originalIM
 	p.originalIM = nil
-	return o, p.tok.Type == EndTagToken
+	return p.tok.Type == EndTagToken
 }
 
 // Section 11.2.5.4.9.
-func inTableIM(p *parser) (insertionMode, bool) {
+func inTableIM(p *parser) bool {
 	switch p.tok.Type {
 	case ErrorToken:
 		// Stop parsing.
-		return nil, true
+		return true
 	case TextToken:
 		// TODO.
 	case StartTagToken:
@@ -861,25 +863,30 @@ func inTableIM(p *parser) (insertionMode, bool) {
 		case "tbody", "tfoot", "thead":
 			p.clearStackToContext(tableScopeStopTags)
 			p.addElement(p.tok.Data, p.tok.Attr)
-			return inTableBodyIM, true
+			p.im = inTableBodyIM
+			return true
 		case "td", "th", "tr":
 			p.clearStackToContext(tableScopeStopTags)
 			p.addElement("tbody", nil)
-			return inTableBodyIM, false
+			p.im = inTableBodyIM
+			return false
 		case "table":
 			if p.popUntil(tableScopeStopTags, "table") {
-				return p.resetInsertionMode(), false
+				p.resetInsertionMode()
+				return false
 			}
 			// Ignore the token.
-			return inTableIM, true
+			return true
 		case "colgroup":
 			p.clearStackToContext(tableScopeStopTags)
 			p.addElement(p.tok.Data, p.tok.Attr)
-			return inColumnGroupIM, true
+			p.im = inColumnGroupIM
+			return true
 		case "col":
 			p.clearStackToContext(tableScopeStopTags)
 			p.addElement("colgroup", p.tok.Attr)
-			return inColumnGroupIM, false
+			p.im = inColumnGroupIM
+			return false
 		default:
 			// TODO.
 		}
@@ -887,20 +894,21 @@ func inTableIM(p *parser) (insertionMode, bool) {
 		switch p.tok.Data {
 		case "table":
 			if p.popUntil(tableScopeStopTags, "table") {
-				return p.resetInsertionMode(), true
+				p.resetInsertionMode()
+				return true
 			}
 			// Ignore the token.
-			return inTableIM, true
+			return true
 		case "body", "caption", "col", "colgroup", "html", "tbody", "td", "tfoot", "th", "thead", "tr":
 			// Ignore the token.
-			return inTableIM, true
+			return true
 		}
 	case CommentToken:
 		p.addChild(&Node{
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return inTableIM, true
+		return true
 	}
 
 	switch p.top().Data {
@@ -909,7 +917,7 @@ func inTableIM(p *parser) (insertionMode, bool) {
 		defer func() { p.fosterParenting = false }()
 	}
 
-	return useTheRulesFor(p, inTableIM, inBodyIM)
+	return inBodyIM(p)
 }
 
 // clearStackToContext pops elements off the stack of open elements
@@ -926,26 +934,26 @@ func (p *parser) clearStackToContext(stopTags []string) {
 }
 
 // Section 11.2.5.4.12.
-func inColumnGroupIM(p *parser) (insertionMode, bool) {
+func inColumnGroupIM(p *parser) bool {
 	switch p.tok.Type {
 	case CommentToken:
 		p.addChild(&Node{
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return inColumnGroupIM, true
+		return true
 	case DoctypeToken:
 		// Ignore the token.
-		return inColumnGroupIM, true
+		return true
 	case StartTagToken:
 		switch p.tok.Data {
 		case "html":
-			return useTheRulesFor(p, inColumnGroupIM, inBodyIM)
+			return inBodyIM(p)
 		case "col":
 			p.addElement(p.tok.Data, p.tok.Attr)
 			p.oe.pop()
 			p.acknowledgeSelfClosingTag()
-			return inColumnGroupIM, true
+			return true
 		}
 	case EndTagToken:
 		switch p.tok.Data {
@@ -953,20 +961,22 @@ func inColumnGroupIM(p *parser) (insertionMode, bool) {
 			if p.oe.top().Data != "html" {
 				p.oe.pop()
 			}
-			return inTableIM, true
+			p.im = inTableIM
+			return true
 		case "col":
 			// Ignore the token.
-			return inColumnGroupIM, true
+			return true
 		}
 	}
 	if p.oe.top().Data != "html" {
 		p.oe.pop()
 	}
-	return inTableIM, false
+	p.im = inTableIM
+	return false
 }
 
 // Section 11.2.5.4.13.
-func inTableBodyIM(p *parser) (insertionMode, bool) {
+func inTableBodyIM(p *parser) bool {
 	var (
 		add      bool
 		data     string
@@ -996,31 +1006,33 @@ func inTableBodyIM(p *parser) (insertionMode, bool) {
 		switch p.tok.Data {
 		case "table":
 			if p.popUntil(tableScopeStopTags, "tbody", "thead", "tfoot") {
-				return inTableIM, false
+				p.im = inTableIM
+				return false
 			}
 			// Ignore the token.
-			return inTableBodyIM, true
+			return true
 		case "body", "caption", "col", "colgroup", "html", "td", "th", "tr":
 			// Ignore the token.
-			return inTableBodyIM, true
+			return true
 		}
 	case CommentToken:
 		p.addChild(&Node{
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return inTableBodyIM, true
+		return true
 	}
 	if add {
 		// TODO: clear the stack back to a table body context.
 		p.addElement(data, attr)
-		return inRowIM, consumed
+		p.im = inRowIM
+		return consumed
 	}
-	return useTheRulesFor(p, inTableBodyIM, inTableIM)
+	return inTableIM(p)
 }
 
 // Section 11.2.5.4.14.
-func inRowIM(p *parser) (insertionMode, bool) {
+func inRowIM(p *parser) bool {
 	switch p.tok.Type {
 	case ErrorToken:
 		// TODO.
@@ -1032,13 +1044,15 @@ func inRowIM(p *parser) (insertionMode, bool) {
 			p.clearStackToContext(tableRowContextStopTags)
 			p.addElement(p.tok.Data, p.tok.Attr)
 			p.afe = append(p.afe, &scopeMarker)
-			return inCellIM, true
+			p.im = inCellIM
+			return true
 		case "caption", "col", "colgroup", "tbody", "tfoot", "thead", "tr":
 			if p.popUntil(tableScopeStopTags, "tr") {
-				return inTableBodyIM, false
+				p.im = inTableBodyIM
+				return false
 			}
 			// Ignore the token.
-			return inRowIM, true
+			return true
 		default:
 			// TODO.
 		}
@@ -1046,21 +1060,23 @@ func inRowIM(p *parser) (insertionMode, bool) {
 		switch p.tok.Data {
 		case "tr":
 			if p.popUntil(tableScopeStopTags, "tr") {
-				return inTableBodyIM, true
+				p.im = inTableBodyIM
+				return true
 			}
 			// Ignore the token.
-			return inRowIM, true
+			return true
 		case "table":
 			if p.popUntil(tableScopeStopTags, "tr") {
-				return inTableBodyIM, false
+				p.im = inTableBodyIM
+				return false
 			}
 			// Ignore the token.
-			return inRowIM, true
+			return true
 		case "tbody", "tfoot", "thead":
 			// TODO.
 		case "body", "caption", "col", "colgroup", "html", "td", "th":
 			// Ignore the token.
-			return inRowIM, true
+			return true
 		default:
 			// TODO.
 		}
@@ -1069,13 +1085,13 @@ func inRowIM(p *parser) (insertionMode, bool) {
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return inRowIM, true
+		return true
 	}
-	return useTheRulesFor(p, inRowIM, inTableIM)
+	return inTableIM(p)
 }
 
 // Section 11.2.5.4.15.
-func inCellIM(p *parser) (insertionMode, bool) {
+func inCellIM(p *parser) bool {
 	var (
 		closeTheCellAndReprocess bool
 	)
@@ -1091,10 +1107,11 @@ func inCellIM(p *parser) (insertionMode, bool) {
 		case "td", "th":
 			if !p.popUntil(tableScopeStopTags, p.tok.Data) {
 				// Ignore the token.
-				return inCellIM, true
+				return true
 			}
 			p.clearActiveFormattingElements()
-			return inRowIM, true
+			p.im = inRowIM
+			return true
 		case "body", "caption", "col", "colgroup", "html":
 			// TODO.
 		case "table", "tbody", "tfoot", "thead", "tr":
@@ -1106,19 +1123,20 @@ func inCellIM(p *parser) (insertionMode, bool) {
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return inCellIM, true
+		return true
 	}
 	if closeTheCellAndReprocess {
 		if p.popUntil(tableScopeStopTags, "td") || p.popUntil(tableScopeStopTags, "th") {
 			p.clearActiveFormattingElements()
-			return inRowIM, false
+			p.im = inRowIM
+			return false
 		}
 	}
-	return useTheRulesFor(p, inCellIM, inBodyIM)
+	return inBodyIM(p)
 }
 
 // Section 11.2.5.4.16.
-func inSelectIM(p *parser) (insertionMode, bool) {
+func inSelectIM(p *parser) bool {
 	endSelect := false
 	switch p.tok.Type {
 	case ErrorToken:
@@ -1167,31 +1185,33 @@ func inSelectIM(p *parser) (insertionMode, bool) {
 			switch p.oe[i].Data {
 			case "select":
 				p.oe = p.oe[:i]
-				return p.resetInsertionMode(), true
+				p.resetInsertionMode()
+				return true
 			case "option", "optgroup":
 				continue
 			default:
 				// Ignore the token.
-				return inSelectIM, true
+				return true
 			}
 		}
 	}
-	return inSelectIM, true
+	return true
 }
 
 // Section 11.2.5.4.18.
-func afterBodyIM(p *parser) (insertionMode, bool) {
+func afterBodyIM(p *parser) bool {
 	switch p.tok.Type {
 	case ErrorToken:
 		// Stop parsing.
-		return nil, true
+		return true
 	case StartTagToken:
 		if p.tok.Data == "html" {
-			return useTheRulesFor(p, afterBodyIM, inBodyIM)
+			return inBodyIM(p)
 		}
 	case EndTagToken:
 		if p.tok.Data == "html" {
-			return afterAfterBodyIM, true
+			p.im = afterAfterBodyIM
+			return true
 		}
 	case CommentToken:
 		// The comment is attached to the <html> element.
@@ -1202,13 +1222,14 @@ func afterBodyIM(p *parser) (insertionMode, bool) {
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return afterBodyIM, true
+		return true
 	}
-	return inBodyIM, false
+	p.im = inBodyIM
+	return false
 }
 
 // Section 11.2.5.4.19.
-func inFramesetIM(p *parser) (insertionMode, bool) {
+func inFramesetIM(p *parser) bool {
 	switch p.tok.Type {
 	case CommentToken:
 		p.addChild(&Node{
@@ -1218,7 +1239,7 @@ func inFramesetIM(p *parser) (insertionMode, bool) {
 	case StartTagToken:
 		switch p.tok.Data {
 		case "html":
-			return useTheRulesFor(p, inFramesetIM, inBodyIM)
+			return inBodyIM(p)
 		case "frameset":
 			p.addElement(p.tok.Data, p.tok.Attr)
 		case "frame":
@@ -1226,7 +1247,7 @@ func inFramesetIM(p *parser) (insertionMode, bool) {
 			p.oe.pop()
 			p.acknowledgeSelfClosingTag()
 		case "noframes":
-			return useTheRulesFor(p, inFramesetIM, inHeadIM)
+			return inHeadIM(p)
 		}
 	case EndTagToken:
 		switch p.tok.Data {
@@ -1234,18 +1255,19 @@ func inFramesetIM(p *parser) (insertionMode, bool) {
 			if p.oe.top().Data != "html" {
 				p.oe.pop()
 				if p.oe.top().Data != "frameset" {
-					return afterFramesetIM, true
+					p.im = afterFramesetIM
+					return true
 				}
 			}
 		}
 	default:
 		// Ignore the token.
 	}
-	return inFramesetIM, true
+	return true
 }
 
 // Section 11.2.5.4.20.
-func afterFramesetIM(p *parser) (insertionMode, bool) {
+func afterFramesetIM(p *parser) bool {
 	switch p.tok.Type {
 	case CommentToken:
 		p.addChild(&Node{
@@ -1255,45 +1277,47 @@ func afterFramesetIM(p *parser) (insertionMode, bool) {
 	case StartTagToken:
 		switch p.tok.Data {
 		case "html":
-			return useTheRulesFor(p, inFramesetIM, inBodyIM)
+			return inBodyIM(p)
 		case "noframes":
-			return useTheRulesFor(p, inFramesetIM, inHeadIM)
+			return inHeadIM(p)
 		}
 	case EndTagToken:
 		switch p.tok.Data {
 		case "html":
-			return afterAfterFramesetIM, true
+			p.im = afterAfterFramesetIM
+			return true
 		}
 	default:
 		// Ignore the token.
 	}
-	return afterFramesetIM, true
+	return true
 }
 
 // Section 11.2.5.4.21.
-func afterAfterBodyIM(p *parser) (insertionMode, bool) {
+func afterAfterBodyIM(p *parser) bool {
 	switch p.tok.Type {
 	case ErrorToken:
 		// Stop parsing.
-		return nil, true
+		return true
 	case TextToken:
 		// TODO.
 	case StartTagToken:
 		if p.tok.Data == "html" {
-			return useTheRulesFor(p, afterAfterBodyIM, inBodyIM)
+			return inBodyIM(p)
 		}
 	case CommentToken:
 		p.doc.Add(&Node{
 			Type: CommentNode,
 			Data: p.tok.Data,
 		})
-		return afterAfterBodyIM, true
+		return true
 	}
-	return inBodyIM, false
+	p.im = inBodyIM
+	return false
 }
 
 // Section 11.2.5.4.22.
-func afterAfterFramesetIM(p *parser) (insertionMode, bool) {
+func afterAfterFramesetIM(p *parser) bool {
 	switch p.tok.Type {
 	case CommentToken:
 		p.addChild(&Node{
@@ -1303,14 +1327,14 @@ func afterAfterFramesetIM(p *parser) (insertionMode, bool) {
 	case StartTagToken:
 		switch p.tok.Data {
 		case "html":
-			return useTheRulesFor(p, afterAfterFramesetIM, inBodyIM)
+			return inBodyIM(p)
 		case "noframes":
-			return useTheRulesFor(p, afterAfterFramesetIM, inHeadIM)
+			return inHeadIM(p)
 		}
 	default:
 		// Ignore the token.
 	}
-	return afterAfterFramesetIM, true
+	return true
 }
 
 // Parse returns the parse tree for the HTML from the given Reader.
@@ -1323,9 +1347,10 @@ func Parse(r io.Reader) (*Node, error) {
 		},
 		scripting:  true,
 		framesetOK: true,
+		im:         initialIM,
 	}
 	// Iterate until EOF. Any other error will cause an early return.
-	im, consumed := initialIM, true
+	consumed := true
 	for {
 		if consumed {
 			if err := p.read(); err != nil {
@@ -1335,11 +1360,11 @@ func Parse(r io.Reader) (*Node, error) {
 				return nil, err
 			}
 		}
-		im, consumed = im(p)
+		consumed = p.im(p)
 	}
 	// Loop until the final token (the ErrorToken signifying EOF) is consumed.
 	for {
-		if im, consumed = im(p); consumed {
+		if consumed = p.im(p); consumed {
 			break
 		}
 	}