Nonoverloadable builtins

The following built-in procs cannot be overloaded for reasons of implementation simplicity (they require specialized semantic checking):

declared, defined, definedInScope, compiles, sizeof,
is, shallowCopy, getAst, astToStr, spawn, procCall

Thus, they act more like keywords than like ordinary identifiers; unlike a keyword however, a redefinition may shadow the definition in the system module. From this list the following should not be written in dot notation x.f since x cannot be type-checked before it gets passed to f:

declared, defined, definedInScope, compiles, getAst, astToStr