D2 map trouble

[Nick Sabalausky]

Trying to convert some D1 code to D2:

On 2.047, I'm trying to do this:

import std.string;
void foo(string str)
{
str =
  std.algorithm.map!(
   (char a) { return inPattern(a, [digits, letters])? a : '_'; }
  )(str);
}

And I'm getting:

delegate std.algorithm.__dgliteral1 cannot access frame of function 
__dgliteral1

What's going on? How do I do it right? I figure I probably have some sort of 
problem with strings being immutable(char)[] instead of char[], but it 
doesn't look like that's the issue it's complaining about. Also, in this 
particular case, I'm not concerned about multi-unit UTF-8 characters.