Type Reflection

[ffi] subr [bool] isnull(val x);
[ffi] subr [bool] islong(val x);
[ffi] subr [bool] isulong(val x);
[ffi] subr [bool] isdouble(val x);
[ffi] subr [bool] isobj(val x, val proto);

The functions isnull, islong, isulong, isdouble, determines whether the value is the special value null, of type long, type ulong, or type double respectively. The function isobj determines whether the value is an object, if proto is not null, then it further determines whether the __proto__ member of the object is equal to proto.