macro compile-time comparison with define-pragmas

[JohnAD]

Rather than explain at great length, a quick bit of source code showing what I 
want to do:
    
    
    #
    # program called with nim c -d:foo=bar test.nim
    #
    
    import std / macros
    
    const foo {.strdefine.} = "unknown"
    
    macro jerry(fooName: untyped): untyped =
      when defined(foo):
        when foo == fooName.strVal:
          result = quote do:
            echo "foo found with a matching value"
        else:
          result = quote do:
            echo "foo found but it does not match"
      else:
        result = quote do:
          echo "foo not found"
    
    
    jerry(bar)
    
    
    Run

It all works if I skip passing the value to the compiler: I get a "foo not 
found". But as soon as I try to examine the ident passed to `jerry`, I can't do 
a compile-time comparison. I get:
    
    
    /home/johnd/Projects/test/test.nim(11, 17) Error: cannot evaluate at 
compile time: fooName
    
    
    Run

I also tried passing in a string literal ( jerry("bar") ) but that didn't help 
any, though clearly the compiler does know the content of a string literal at 
compile-time.

In other words, I am trying to change the macro output by comparing a local 
source-code reference to a compiler switch.

Anyone one know of a way to do something like this?

Alternatively, is it possible to get the context of the current "source code 
filename" at compile time?