Re: Why are Ada compilers difficult to write ?

["Dan'l Miller" <optikos@verizon.net>]

On Thursday, June 21, 2018 at 12:42:44 PM UTC-5, Pascal Obry wrote:
> Freezing rules come to mind.

C++ has an analogous compiler-writing difficulty:  entities may be utilized in bodies of member functions prior to being declared later on in the same class declaration.  This requires effective postponement of compilation of member-function bodies until after the closing } of the class.

That said, Ada's freezing rules seem to be less uniform that C++'s, and thus more complex by some measure.  (It is remotely imaginable that Ada in some alternate universe could have had one simple freezing rule:  keep all the clay soft until the absolutely very last token (i.e., the semicolon) of the private part of the package declaration, and then freeze only there at the •closing/terminating end• of the private section of the package declaration.)

Pascal, what makes freezing rules difficult when writing Ada compilers? 
1) Is it that the freezing occurs later than what the compiler writer would find convenient, forcing the compiler writer to keep clay soft when it already seems to be in the kiln?
2) Is it that freezing occurs prematurely, requiring the compiler writer to expend effort enforcing the freezing too early for no good reason?
3) Is it that freezing rules are non-uniform/arbitrary/capricious across language constructs?
4) Something else?
5) All of the above?