How to pass an InputRange of dchars to a function that wants an Input range of chars?

[realhet]

Hello,

The problematic line is at the very bottom.

I only managed to make it run by precedding the .byChar with 
.text, but that is unwanted because it would convert the whole 
InputRange.

How can I do this dchar->char conversion on only the required 
number of chars? (The kwSearch function will pop only a few 
chars, it doesn't whant a whole RandomAccessRange)

```D
import std;

struct KeywordSearchTree
{
	char ch/+root is always 0xff, it is there to hold subNodes.+/;
	int code;
	KeywordSearchTree[] subNodes;
	
	void addSubNode(string s, int scode)
	{
		if(s.length==0) return;
		
		auto idx = subNodes.map!"a.ch".countUntil(s[0]);
		if(idx<0) { idx = subNodes.length; subNodes ~= 
KeywordSearchTree(s[0]); }
		
		if(s.length==1)	subNodes[idx].code = scode;
		else	subNodes[idx].addSubNode(s[1..$], scode);
	}
	
	static KeywordSearchTree build(string[] keywords)
	{
		KeywordSearchTree root;
		foreach(i, act; keywords)
		root.addSubNode(act, (cast(int)(i+1)));
		return root;
	}
}

int kwSearch(KeywordSearchTree tree, R)(R s)
if(isInputRange!(R, immutable char))
{
	//pragma(msg, __FUNCTION__);
	
	if(s.empty) return 0;
	switch(s.front)
	{
		static foreach(sn; tree.subNodes)
		{
			case sn.ch: {
				s.popFront;
				if(!s.empty) if(const res = kwSearch!sn(s)) return res;
				return sn.code;
			}
		}
		default: return 0;
	}
}

int kwSearch(string[] keywords, R)(R s)
if(isInputRange!(R, immutable char))
{
	enum tree = KeywordSearchTree.build(keywords);
	return kwSearch!tree(s);
}

string[] keywords;

void main()
{
	enum ctKeywords = [
		"!", //Link: shebang https://dlang.org/spec/lex.html#source_text
		"version", "extension", "line", 	//Link: GLSL directives
		"pragma", "warning", "error", "assert", 	//Link: Opencl 
directives
		"include", "define", "undef", "ifdef", "ifndef", "if", "else", 
"elif", "endif",  	//Link: Arduino directives
	];
	keywords = ctKeywords;
	
	foreach(kw; keywords)
	{ (kw.dtext~" garbage"d).byChar.kwSearch!ctKeywords.writeln; }
}
```