----- Original Message ----- From: "Frank Heckenbach" <ih8mj@fjf.gnu.de> To: <gpc@gnu.de> Sent: Thursday, April 06, 2006 18:25 Subject: Re: Out of range values in

Bart van den Broek wrote:

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If I (as an inactive observer) may comment / make a suggestion; when a constant of ByteBoole, WordBoole or LongBoole is evaluated, presumably at compile time, convert it to a value of type Boolean. As a consequence: type VeryTrue = ByteBool (10) .. ByteBool (42); means type VeryTrue = True..True; Also, in the test program fjf1102, (Ord (a) = 1) and (Ord (b) = 1) and (Ord (c) = 1) holds, and more specifically Ord( ByteBool(42) ) = 1.

Interesting idea, but if done only for constants (as I understand your suggestion), it would also lead to strange effects:

program foo;

var n: Integer = 42;

begin WriteLn (ByteBool (n) = ByteBool (42)) { => False } end.

Since the Borland Delphi 3 Object Pascal Language Guide mentions: "....Whenever a ByteBool, WordBool or LongBool value is used in a context where a Boolean value is expected, the compiler will automatically generate code that converts any nonzero value to the value True." If i interpret the expression ByteBool(n) = ByteBool(42) as "a context where a Boolean value is expected" then it is equivalent to (ByteBool(n) <> 0) = (ByteBool(42) <> 0), or (ByteBool(n) <> 0) = True, and foo would print True.

I don't think so (BTW, what does Delphi do?). The context here is `=' Since ByteBool is an ordinal type, and `=' allows the same ordinal type (among others) on both sides, ByteBool is valid. I.e., it's a context where Boolean is allowed, but not required. Contexts that require Boolean include the conditions in if, while, until, or assignments to Boolean variables, or Boolean value parameters.

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Besides, it probably wouldn't be 100% Delphi compatible, as Delphi documentation (as quoted by Adriaan) states that Ord of "True" of such types can be any value <> 0.

Well, 1 is such a value <> 0, so how do u think it is incompatible?

OK, but if it were always 1, then they'd probably say so, and not write:

: Boolean ByteBool, WordBool, LongBool : Ord( True) = 1 Ord( True) = any non-zero value

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I dont have Delphi available right now, but i vaguely remember Delphi does the following: ByteBool(True) = $FF WordBool(True) = $FFFF LongBool(True) = $FFFFFF If so (will check later) then this means my suggestion is different and maybe incompatible.

I don't either, but someone who does might want to check this (and the behaviour of my program above under Delphi). If really ByteBool(True) = $FF (I assume you mean Ord (ByteBool (True)) = $FF, or can you compare ByteBool and integers in Delphi?) that would complicate things, as normally (in BP and GPC) value type casts preserve ordinal values ...

Frank

-- Frank Heckenbach, frank@g-n-u.de, http://fjf.gnu.de/, 7977168E GPC To-Do list, latest features, fixed bugs: http://www.gnu-pascal.de/todo.html GPC download signing key: ACB3 79B2 7EB2 B7A7 EFDE D101 CD02 4C9D 0FE0 E5E8

Indeed I meant Ord(ByteBool(True)) = $FF and so on. When I run this program in Delphi v7.1 (7.0 + patch) program Project1; {$APPTYPE CONSOLE} procedure RunTest; var n : Integer; m : Integer; begin n := 42; m := 43; Writeln(ByteBool(n) = ByteBool(m)); Writeln(ByteBool(n) = ByteBool(42)); Writeln(ByteBool(n) = True); Writeln(Ord(ByteBool(True))); Writeln(WordBool(n) = WordBool(m)); Writeln(WordBool(n) = WordBool(42)); Writeln(WordBool(n) = True); Writeln(Ord(WordBool(True))); Writeln(LongBool(n) = LongBool(m)); Writeln(LongBool(n) = LongBool(42)); Writeln(LongBool(n) = True); Writeln(Ord(LongBool(True))); Writeln(Pred(Boolean(False))); Writeln(Pred(ByteBool(False))); Writeln(Pred(WordBool(False))); Writeln(Pred(LongBool(False))); end; begin RunTest; end. I get this output (ignore extra empty lines i put in): TRUE TRUE TRUE 255 TRUE TRUE TRUE 65535 TRUE TRUE TRUE -1 <gibberish> <gibberish> TRUE TRUE Note the signedness of the Ord(LongBool(True)), probably due to the fact that Ord function is 32 bits integer. I guess being completely compatible here is not simple. Bart