gistfile1.txt

    public static P6any GetNumber(Variable v, P6any o, out int rank) {
        if (o.mo.num_rank >= 0) {
            rank = o.mo.num_rank;
        } else {
            if (o.Does(Kernel.RealMO)) { # new code starts here
                rank = NR_FLOAT;
                return MakeFloat(o.InvokeMethod(Kernel.GetInferiorRoot(), "Bridge", null, null));
            } else {                     # and ends here
                o = o.mo.mro_Numeric.Get(v).Fetch();
                rank = o.mo.num_rank;
                if (rank < 0)
                    throw new NieczaException("Not a valid primitive number " +
                            o.mo.name);
            }
        }
        if (rank == NR_FIXINT && o is BoxObject<BigInteger>)
            rank = NR_BIGINT;
        return o;
    }

<new Real type>.abs gets me

Unhandled exception: System.InvalidCastException: Cannot cast from source type to destination type.
  at Builtins.PromoteToFloat (Int32 rank, Niecza.P6any vret) [0x00000] in <filename unknown>:0 
  at Builtins.abs (Niecza.Variable a1) [0x00000] in <filename unknown>:0 
  at Run.CORE.C967prefix:<abs> (Niecza.Frame ) [0x00000] in <filename unknown>:0 
  at Niecza.Kernel.RunCore (Niecza.Frame& cur) [0x00000] in <filename unknown>:0 
  at /Users/colomon/tools/niecza/lib/CORE.setting line 0 (prefix:<abs> @ 1) 
  at /Users/colomon/tools/niecza/lib/CORE.setting line 364 (Cool.abs @ 3) 
  at /Users/colomon/tools/niecza/t/spec/S32-num/real-bridge.t line 44 (mainline @ 23)