D almost has concepts (lite)

[TommiT]

TDPL says:

"D defines a simple partial ordering relation for functions: if 
foo1 can be called with the parameter types of foo2, then foo1 ≤ 
foo2."

If you made the slightest change in the wording, you'd basically 
get the current C++ concepts-lite proposal in D:

"D defines a simple partial ordering relation for functions: if 
foo1 can be called with all the possible arguments that foo2 can 
be called with, then foo1 ≤ foo2."

At first, it almost sounds like the same statement, but now this 
would compile:

void fun(T)(T) if (T.sizeof >= 2) { }
void fun(T)(T) if (T.sizeof >= 4) { }

void main()
{
     fun(42); //calls the second one
}

I don't know if D would be better like that, but I just wanted 
point out how close the spec is to saying that.