Small poll

[Kostis Sagonas]

Robert Virding wrote a mail quoting my mail, and he finished it as
follows:

 > ... deleted ...
 >
 > Sorry for getting worked up about this but I wish people would think
 > through their suggestions a bit more and consider the deeper
 > implications of them.
 > 
 > Finally one definite reason not to outlaw a+42 is that it is one of my
 > standard ways of generating an error in code, being much shorter to
 > write than exit(some_bogus_exit_value).

I will try to avoid the temptation of replying directly to the first
statement above, and instead reply to the following question of Robert.

 > 3. What is the point is the compiler transforming it to
 >    exit({badarith,...})? What are you exactly gaining by doing it?
 >    Not saving code anyway, and hardly runtime either. 


Ah, Robert, you seem to have very limited imagination... let me help
you here.  Consider the code:

	-module(a42).
	-export([test/0]).

	test() ->
	  catch f(),
	  ok.
	
	f() when a+42 == 0 ->
	  %% extremely long sequence of code here
	  ok_1;
	f() ->
	  Y = ackerman(), % very long computation here
			  % (without side-effects)
	  X = a+42,
	  mod:funct(X,Y),
	  %% possibly lots more other code here
	  ok_2.

	ackerman() -> .... 


QUESTION 1
----------
Do the "semantics" of Erlang (BTW, I would really like to see them
formally specified before people use this term again) allow a compiler
to transform the code above to just:

	-module(a42).
        -export([test/0]).

        test() ->
	  ok.

QUESTION 2
----------
Can the savings in time and code space be made arbitrarily big, or not?

QUESTIONS 3-N
-------------
 - Do the two occurrences of "a+42" need to be treated differently
   by the compiler in the above example, or not?
 - Is "a+42" an expression that always generates an error in Erlang?
	(as far as the user is concerned)
 - Is it just me that finds this Erlang-ism confusing to say
   the least?  (I.e., is this a user-friendly language design?)


Kostis.

PS. I am very well aware that the subject has shifted from
    warnings vs. errors to something else now, but I could
    not resist.  Apologies.