Rhelper=function(topic)
{
	## Window and containers
	window.main=gtkWindow("toplevel",show=FALSE);
	window.main$setTitle("Rhelper");
	window.main$setDefaultSize(800,600);
	hbox.main=gtkHBoxNew(homogeneous=FALSE);
	vbox.left=gtkVBoxNew(homogeneous=FALSE);
	sw1.main=gtkScrolledWindowNew(show=TRUE);
	sw2.main=gtkScrolledWindowNew(show=TRUE);
	sw1.main$setPolicy(GtkPolicyType["automatic"],GtkPolicyType["automatic"]);
	sw2.main$setPolicy(GtkPolicyType["automatic"],GtkPolicyType["automatic"]);
	sw1.main$setSizeRequest(200,-1);
	## Font style
	font.style=pangoFontDescriptionNew();
	#font.style$setSize(10);
	font.style$setFamily("sans");
	## ComboBox
	combo.label=gtkLabelNew("Select package:");
	gtkMiscSetAlignment(combo.label,0,0.5);
	gtkWidgetModifyFont(combo.label,font.style);
	combo.label$setSizeRequest(-1,25);
	combo.main=gtkComboBoxNewText();
	pkgs=.packages(TRUE);
	for(pkg in pkgs)
	{
		gtkComboBoxAppendText(combo.main,pkg);
	}
	## Filter
	filter.label=gtkLabelNew("Filter:");
	gtkMiscSetAlignment(filter.label,0,0.5);
	gtkWidgetModifyFont(filter.label,font.style);
	filter.label$setSizeRequest(-1,25);
	filter.main=gtkEntryNew();
	## Listbox
	model.main=gtkListStoreNew("gchararray");
	listbox.main=gtkTreeViewNewWithModel(model.main);
	renderer.main=gtkCellRendererTextNew();
	column.main=gtkTreeViewColumnNewWithAttributes("",renderer.main,text=0);
	column.header=gtkLabelNew();
	gtkWidgetModifyFont(column.header,font.style);
	column.header$setSizeRequest(-1,25);
	column.main$setWidget(column.header);
	listbox.main$appendColumn(column.main);
	selection.main=gtkTreeViewGetSelection(listbox.main);
	selection.main$setMode(GtkSelectionMode["single"]);
	setListbox=function(topic,widget,pattern=NULL)
	{
		model=widget$getModel();
		column=widget$getColumn(0);
		selection=widget$getSelection();
		
		helpfile=as.character(help(topic))[1];
		pkgname=basename(dirname(dirname(helpfile)));
		indexfile=file.path(dirname(helpfile),"AnIndex");
		fun.name=readLines(indexfile);
		fun.name=gsub("\t.*","",fun.name);
		reload=(pkgname!=gsub("Package: ","",column$getWidget()$getText()));
		if(!is.null(pattern))
		{
			fun.name=grep(pattern,fun.name,value=TRUE,fixed=TRUE);
			if(!length(fun.name)) 
			{
				model$clear();
				return(FALSE);
			}
			if(!(topic %in% fun.name)) topic=fun.name[1];
			reload=TRUE;
		}
		if(reload)
		{
			model$clear();
			for(fname in fun.name)
			{
				.RGtkCall("S_gtk_list_store_set_value",model,
								gtkListStoreAppend(model)$iter,
								0L,fname,PACKAGE="RGtk2");
			}
			column$getWidget()$setText(paste("Package:",pkgname));
		}
		index=which(fun.name==topic)[1]-1;
		list.path=gtkTreePathNewFromIndices(index);
		selection$selectPath(list.path);
		widget$scrollToCell(list.path,NULL,FALSE,NULL,NULL);
	}
	## TextView
	buffer.main=gtkTextBufferNew();
	textview.main=gtkTextView(buffer=buffer.main,show=TRUE);
	textview.main$setEditable(FALSE);
	textview.main$setWrapMode(GtkWrapMode["word"]);
	textview.main$setLeftMargin(10);
	textview.main$setRightMargin(10);
	## Tags
	tag.title=buffer.main$createTag("title",
			family="serif",scale=PANGO_SCALE_XX_LARGE,
			weight=PangoWeight["bold"],justification="center",
			pixels_above_lines=20,pixels_below_lines=20);
	tag.section=buffer.main$createTag("section",
			family="serif",scale=PANGO_SCALE_X_LARGE,
			weight=PangoWeight["bold"],pixels_above_lines=15,
			pixels_below_lines=12);
	tag.text=buffer.main$createTag("text",scale=PANGO_SCALE_LARGE,
			family="sans",pixels_above_lines=8,pixels_below_lines=8);
	tag.code=buffer.main$createTag("code",foreground="#666666",
			scale=PANGO_SCALE_LARGE,weight=PangoWeight["bold"],
			family="monospace",pixels_above_lines=8,
			pixels_below_lines=8);
	tag.pre=buffer.main$createTag("pre",scale=PANGO_SCALE_LARGE,
			family="monospace");
	tag.emph=buffer.main$createTag("emph",style="italic",
			scale=PANGO_SCALE_LARGE,left_margin=50,
			pixels_above_lines=8,pixels_below_lines=8);
	tag.bold=buffer.main$createTag("bold",family="sans",scale=PANGO_SCALE_LARGE,
			weight=PangoWeight["bold"],pixels_above_lines=8,
			pixels_below_lines=8);
	tag.arg=buffer.main$createTag("arg",foreground="#666666",
			scale=PANGO_SCALE_LARGE,weight=PangoWeight["bold"],
			family="monospace");
	tag.discrip=buffer.main$createTag("discrip",left_margin=50);
	tags.available=c("title","section","text","code","pre","emph",
				 	"bold","arg","discrip","link");
	## Rd parser
	parser=function(topic)
	{
		helpfile=as.character(help(topic))[1];
		pkgname=basename(dirname(dirname(helpfile)));
		docname=basename(helpfile);
		RdDB=file.path(dirname(helpfile),pkgname);
		Rdobj=tools:::fetchRdDB(RdDB,docname);
		
		doc=as.character(Rdobj);
		# symbols
		src=c("\\R","\\dots","\\ldots","\\sqrt","\\ge","\\le",
				"\\alpha","\\beta","\\gamma","\\delta","\\epsilon","\\zeta",
				"\\eta","\\theta","\\iota","\\kappa","\\lambda","\\mu","\\nv",
				"\\xi","\\omicron","\\pi","\\rho","\\sigma","\\tau","\\upsilon",
				"\\phi","\\chi","\\psi","\\omega","\\Alpha","\\Beta","\\Gamma",
				"\\Delta","\\Epsilon","\\Zeta","\\Eta","\\Theta","\\Iota",
				"\\Kappa","\\Lambda","\\Mu","\\Nv","\\Xi","\\Omicron","\\Pi",
				"\\Rho","\\Sigma","\\Tau","\\Upsilon","\\Phi","\\Chi","\\Psi",
				"\\Omega");
		target=c("R","...","...","√","≥","≤","α","β","γ","δ","ε","ζ","η","θ",
				"ι","κ","λ","μ","ν","ξ","ο","π","ρ","σ","τ","υ","φ","χ","ψ","ω",
				"Α","Β","Γ","Δ","Ε","Ζ","Η","Θ","Ι","Κ","Λ","Μ","Ν","Ξ","Ο","Π",
				"Ρ","Σ","Τ","Υ","Φ","Χ","Ψ","Ω");
		for(i in 1:length(src))
		{
			doc=gsub(src[i],target[i],doc,fixed=TRUE);
		}
		# Remove null string.
		doc=doc[doc!=""];
		# Remove the NL in the beginning and at the end of a section.
		left=(1:length(doc))[doc=="{"];
		right=(1:length(doc))[doc=="}"];
		doc[left+1]=gsub("^\n","",doc[left+1]);
		doc[right-1]=gsub("\n$","",doc[right-1]);
		# attributes of tags
		square.br=(1:length(doc))[doc=="["];
		if(length(square.br))
		{
			for(index in square.br)
			{
				if(grepl("^\\\\",doc[index-1]))
				{
					doc[index-1]=paste(doc[index-1],doc[index+1],sep="");
					doc[(index):(index+2)]="";
				}
			}
		}
		# brace
		brace.pair=function(doc)
		{
			left=(1:length(doc))[doc=="{"];
			right=(1:length(doc))[doc=="}"];
			s=rbind(cbind(left,1),cbind(right,-1));
			s=s[order(s[,1]),];
			n=dim(s)[1];
			left.pair=sapply(left,function(x){
				i=which(s[,1]==x)[1];
				index=which(cumsum(s[i:n,2])==0)[1]+i-1;
				return(s[index,1]);
			});
			return(cbind(left,left.pair));
		}
		# Add prefixes and suffixes to the content in {}.
		doc.add=as.list(doc);
		doc.add[doc=="{"]="PrEfIx";
		doc.add[doc!="{"]=list(NULL);
		doc=mapply(function(x,y) c(x,y),doc,doc.add,SIMPLIFY=FALSE,USE.NAMES=FALSE);
		doc.add[doc=="}"]="SuFfIx";
		doc.add[doc!="}"]=list(NULL);
		doc=mapply(function(x,y) c(x,y),doc.add,doc,SIMPLIFY=FALSE,USE.NAMES=FALSE);
		doc=unlist(doc);
		# selector
		selector=function(tag,doc,brace.pairs)
		{
			tag.name=paste("^\\\\",tag,sep="");
			header=grep(tag.name,doc);
			if(!length(header)) return(NULL);
			
			n=length(doc);
			left.all=(1:n)[doc=="{"];
			header0=intersect(header,left.all-1);
			if(!length(header0)) return(list("header"=header));
			
			header=header0;
			left1=header+1;
			right1=brace.pairs[match(left1,brace.pairs[,1]),2];
			prefix1=left1+1;
			suffix1=right1-1;
			content1=unlist(mapply(function(x,y) x:y,prefix1+1,suffix1-1),use.names=FALSE)
			
			left2=intersect(left.all,right1+1);
			if(!length(left2)) return(list("header"=header,"left1"=left1,
								"prefix1"=prefix1,"content1"=content1,
								"suffix1"=suffix1,"right1"=right1));
			right2=brace.pairs[match(left2,brace.pairs[,1]),2];
			prefix2=left2+1;
			suffix2=right2-1;
			content2=unlist(mapply(function(x,y) x:y,prefix2+1,suffix2-1),use.names=FALSE)
			return(list("header"=header,"left1"=left1,"prefix1"=prefix1,
								"content1"=content1,"suffix1"=suffix1,
								"right1"=right1,"left2"=left2,"prefix2"=prefix2,
								"content2"=content2,"suffix2"=suffix2,"right2"=right2));
		}
		doc=doc[doc!=""];
		brace.pairs=brace.pair(doc);
		# Find the space to be preserved.
		space.usage=selector("usage",doc,brace.pairs)$content1;
		space.examples=selector("examples",doc,brace.pairs)$content1;
		space.preformatted=selector("preformatted",doc,brace.pairs)$content1;
		space.pre=c(space.usage,space.examples,space.preformatted);
		doc[space.pre]=paste("SpAcEpReSeRvEd",doc[space.pre],sep="");
		doc=gsub("^  +","",doc);
		doc=gsub("SpAcEpReSeRvEd","",doc);
		# Find the NL to be preserved.
		doc=gsub("^ +\n$","\n",doc);
		NL.end=grep(".+\n$",doc);
		NL.arg=selector("arguments",doc,brace.pairs)$content1;
		NL.item=selector("item$",doc,brace.pairs);
		NL.item=c(NL.item$content1,NL.item$content2);
		NL.describe=selector("describe",doc,brace.pairs)$content1;
		NL.single=(1:length(doc))[doc=="\n"];
		NL.pre1=intersect(c(NL.end+1,NL.describe,setdiff(NL.arg,NL.item)),NL.single);
		NL.pre2=space.usage;
		NL.pre3=space.examples;
		NL.pre4=space.preformatted;
		NL.pre=unique(c(NL.pre1,NL.pre2,NL.pre3,NL.pre4));
		doc[NL.pre]=gsub("\n$","NlPrEsErVeD",doc[NL.pre]);
		# Convert unproteced NL to space.
		doc=gsub("\n$"," ",doc);
		doc=gsub("NlPrEsErVeD","\n",doc);
		# some replacements
		doc[doc=="\\special"]="";
		doc[doc=="\\itemize"]="\\enumerate";
		content=selector("sQuote",doc,brace.pairs);
			doc[c(content$prefix1,content$suffix1)]="\'";
			doc[c(content$header,content$left1,content$right1)]="";
		content=selector("dQuote",doc,brace.pairs);
			doc[c(content$prefix1,content$suffix1)]="\"";
			doc[c(content$header,content$left1,content$right1)]="";
		# Delete tags that will not be displayed.
		tags.delete=c("name","alias","concept","keyword","dontshow");
		for(tag in tags.delete)
		{
			content=selector(tag,doc,brace.pairs);
			doc[unlist(content,use.names=FALSE)]="";
		}
		# about the "section" tag
		content=selector("section",doc,brace.pairs);
		doc[content$header]=paste("\\section: ",doc[content$content1],sep="");
		doc[c(content$left1,content$prefix1,content$content1,content$suffix1,
						content$right1)]="";
		# about the "method" tag
		content=selector("method",doc,brace.pairs);
		fun=doc[content$content1];
		doc[content$content1]=paste("## S3 method for class \'",doc[content$content2],"\'\n",sep="");
		doc[content$content2]=fun;
		doc[c(content$header,content$left1,content$right1,
						content$prefix1,content$suffix1)]="";
		# about the "describe" tag
		content=selector("describe",doc,brace.pairs);
		doc[content$content1]=gsub("\\\\code","",doc[content$content1]);
		doc[c(content$header,content$left1,content$right1,content$suffix1)]="";
		doc[content$prefix1]="\n";
		# equations
		content=selector("d?eqn",doc,brace.pairs);
		has2parts=match(content$left2-1,content$right1);
		doc[c(content$left1[has2parts],content$prefix1[has2parts],
						content$content1[has2parts],content$suffix1[has2parts],
						content$right1[has2parts])]="";
		# deqn
		doc=doc[doc!=""];
		brace.pairs=brace.pair(doc);
		content=selector("deqn",doc,brace.pairs);
		doc[c(content$prefix1,content$suffix1)]="\n";
		doc[doc=="\\eqn"|doc=="\\deqn"]="\\emph";
		# Add NL to the head and tail of sections.
		doc[c(1:3,6)]="";
		doc[5]="\n";
		names(doc)[4]="title";
		doc=doc[doc!=""];
		brace.pairs=brace.pair(doc);
		sections=c("description","usage","arguments","details",
				"value","references","note","author","seealso","examples",
				"source","format");
		sections.name=c("Description","Usage","Arguments","Details",
				"Value","References","Note","Author(s)","See Also","Examples",
				"Source","Format");
		
		content=selector("usage",doc,brace.pairs);
		names(doc)[content$content1]="pre";
		content=selector("examples",doc,brace.pairs);
		names(doc)[content$content1]="pre";
		for(i in 1:length(sections))
		{
			content=selector(sections[i],doc,brace.pairs);
			doc[c(content$prefix1,content$suffix1)]="\n";
			doc[c(content$left1,content$right1)]="";
			doc[content$header]=sections.name[i];
			names(doc)[content$header]="section";
		}
		content=selector("section",doc,brace.pairs);
		doc[c(content$prefix1,content$suffix1)]="\n";
		doc[c(content$left1,content$right1)]="";
		doc[content$header]=gsub("\\\\section: ","",doc[content$header]);
		names(doc)[content$header]="section";
		
		content=selector("enumerate",doc,brace.pairs);
		doc[content$suffix1]="\n";
		
		content=selector("preformatted",doc,brace.pairs);
		doc[content$content1]=gsub("^ +$","",doc[content$content1]);
		doc[content$right1+1]=gsub("^ +$","",doc[content$right1+1]);
		doc[c(content$prefix1,content$suffix1)]="\n";
		# item
		content=selector("item",doc,brace.pairs);
		item.all=grep("^\\\\item",doc);
		item.nopar=setdiff(item.all,content$header);
		doc[item.nopar]="\n●";
		names(doc)[content$content1]="arg";
		doc[content$header-1]=gsub("^ +$","",doc[content$header-1]);
		doc[c(content$header,content$left1,content$right1)]="";
		names(doc)[content$content2]="discrip";
		doc[c(content$left2,content$right2)]="";
		doc[content$prefix2]="\n";
		# dontrun
		content=selector("dontrun",doc,brace.pairs);
		doc[content$prefix1]="## Not run:\n";
		doc[content$suffix1]="\n## End(Not run)\n";
		doc[c(content$header,content$left1,content$right1)]="";
		# Replace tags.
		# Fix: kbd, href, dfn, cite, acronym
		doc[doc=="\\env" | doc=="\\command" | doc=="\\preformatted" | doc=="\\option"]="\\pre";
		doc[doc=="\\strong" | doc=="\\pkg" | doc=="\\email"]="\\bold";
		doc[doc=="\\samp" | doc=="\\file" | doc=="\\verb"]="\\code";
		doc[doc=="\\enumerate"]="\\discrip";
		doc[doc=="\\var" | doc=="\\kbd"]="\\emph";
		doc[doc=="\\url"]="\\link";
		doc[doc=="\\donttest"]="";
		# Set the format of texts by tags.
		doc=doc[doc!=""];
		brace.pairs=brace.pair(doc);
		# discrip -> code -> emph -> link	The order is important.
		tags.format=c("discrip","pre","bold","code","emph","link");
		for(tag in tags.format)
		{
			content=selector(tag,doc,brace.pairs);
			names(doc)[content$content1]=paste(names(doc)[content$content1],tag,sep=".")
			doc[c(content$header,content$left1,content$right1,content$prefix1,content$suffix1)]="";
		}
		doc[doc=="{" | doc=="}" | doc=="PrEfIx" | doc=="SuFfIx"]="";
		doc=doc[doc!=""];
		names(doc)[is.na(names(doc))]="text";
		names(doc)=gsub("NA\\.","",names(doc));
		names(doc)=gsub("code\\.link","link",names(doc));
		names(doc)[names(doc)=="discrip"]="discrip.text";
		return(doc);
	}
    ## Write text
	writeText=function(topic,buf)
	{
		doc=parser(topic);
		
		buf$setText("");
		iter.t=buf$getIterAtOffset(0)$iter;
		for(i in 1:length(doc))
		{
			tags=unlist(strsplit(names(doc)[i],"\\."));
			tags=intersect(tags,tags.available);
			if("link" %in% tags)
			{
				tag.link=buf$createTag(NULL,foreground="blue",underline="single",
							scale=PANGO_SCALE_LARGE,weight=PangoWeight["bold"],
							family="monospace",pixels_above_lines=8,
							pixels_below_lines=8);
				tag.link$setData("link",doc[i]);
				buf$insertWithTags(iter.t,doc[i],tag.link);
			}else{
				.RGtkCall("S_gtk_text_buffer_insert_with_tags_by_name",
							buf,iter.t,doc[i],tags);
			}
		}
	}
	## Signal
	combo_changed=function(widget,param)
	{
		pkg=widget$getActiveText();
		if(!require(pkg,character.only=TRUE)) return(FALSE);
		topic=ls(paste("package:",pkg,sep=""))[1];
		setListbox(topic,param$listbox);
		return(FALSE);
	}
	selection_changed=function(widget,param)
	{
		if(!widget$getSelected()$retval) return(FALSE);
		iter=widget$getSelected()$iter;
		topic=param$model$getValue(iter,0)$value;
		writeText(topic,param$buffer);
		return(FALSE);
	}
	key_pressed=function(widget,event,param)
	{
		if(event$keyval!=65293) return(FALSE);
		pkg=param$listbox$getColumn(0)$getWidget()$getText();
		pkg=gsub("Package: ","",pkg);
		topic=ls(paste("package:",pkg,sep=""))[1];
		pattern=widget$getText();
		setListbox(topic,param$listbox,pattern);
		return(FALSE);
	}
	link_clicked=function(widget,event,param)
	{
		if(event$type!=GdkEventType['button-release']-1) return(FALSE);
		if(event$button!=1) return(FALSE);
		buffer=widget$getBuffer();
		iter.bounds=buffer$getSelectionBounds();
		if(iter.bounds$start$getOffset()!=iter.bounds$end$getOffset()) return(FALSE);
		buffer.coords=widget$windowToBufferCoords(GtkTextWindowType["widget"],event$x,event$y);
		iter=widget$getIterAtLocation(buffer.coords$buffer.x,buffer.coords$buffer.y)$iter;
		if(!length(iter$getTags())) return(FALSE);
		link=iter$getTags()[[1]]$getData("link");
		if(!is.null(link))
		{
			if(!grepl("^http",link))
			{
				setListbox(link,param$listbox);
			}else browseURL(link);
		}
		return(FALSE);
	}
	gSignalConnect(combo.main,"changed",combo_changed,list(listbox=listbox.main));
	gSignalConnect(selection.main,"changed",selection_changed,list(model=model.main,buffer=buffer.main));
	gSignalConnect(filter.main,"key-press-event",key_pressed,list(listbox=listbox.main));
	gSignalConnect(textview.main,"event-after",link_clicked,list(listbox=listbox.main));
	## Initialize
	setListbox(topic,listbox.main);
	## Show window
	window.main$add(hbox.main);
	hbox.main$packStart(vbox.left,FALSE,FALSE,2);
	hbox.main$packStart(sw2.main);
	vbox.left$packStart(combo.label,FALSE,FALSE);
	vbox.left$packStart(combo.main,FALSE,FALSE);
	vbox.left$packStart(filter.label,FALSE,FALSE);
	vbox.left$packStart(filter.main,FALSE,FALSE);
	vbox.left$packStart(sw1.main);
	sw1.main$add(listbox.main);
	sw2.main$add(textview.main);
	window.main$show();
}