In DMD 2.051, std.functional, line 53:
enum testAsStmts = "{"~ElementType.stringof~" "~parmName~"; "~fun~"}()";

I think the line is missing a semicolon after "~fun~". Fixed:
enum testAsStmts = "{"~ElementType.stringof~" "~parmName~"; "~fun~";}()";

But the code that uses the enum is commented out for some reason.

Line 250, binaryReverseArgs:

Why not replace this complex return type:
    typeof({ ElementType1 a; ElementType2 b; return pred(b, a);}())
    binaryReverseArgs(ElementType1, ElementType2)(ElementType1 a,
            ElementType2 b)
    {
        return pred(b, a);
    }

with the simpler:
    auto binaryReverseArgs(ElementType1, ElementType2)(ElementType1 a,
            ElementType2 b)
    {
        return pred(b, a);
    }

unittests will still pass.