[fpc-pascal] precedence "is" and "and"
Hi,
According to the docs, the "is" operator is fourth level, the "and" is
second level, so the "and" must be computed before the "is". But it
seems fpc treats "is" and "and" as same level:
{$mode objfpc}
uses Classes;
var
b: boolean;
o: TObject;
begin
// this compiles, but should fail:
if o is TComponent and b then ;
// this fails, correct
if b and o is TComponent then ;
// for completeness, this fails:
if TComponent and b then ;
end.
The strange thing, is that the Delphi compiler works as fpc and the
Delphi docs says the same as the fpc docs:
http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Expressions_(Delphi)#Operator_Precedence
Mattias
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Re: [fpc-pascal] precedence "is" and "and"
On Sat, 8 Dec 2018 20:38:23 +0100 Mattias Gaertner via fpc-pascal wrote: >[...] > According to the docs, the "is" operator is fourth level, the "and" is > second level, so the "and" must be computed before the "is". But it > seems fpc treats "is" and "and" as same level: >[...] Btw, there is a difference between fpc and delphi treating "is" and "or" precedence. The following compiles in fpc, but not in Delphi: if b or o is TComponent then ; Same with "xor". This compiles in fpc and Delphi: if o is TComponent or b then ; It seems under Delphi "is", "and", "or", "xor" have the same precedence level and the Delphi docs are wrong. Mattias ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] precedence "is" and "and"
On Sat, 8 Dec 2018 20:38:23 +0100 Mattias Gaertner via fpc-pascal wrote: > Hi, > > According to the docs, the "is" operator is fourth level, the "and" is > second level, so the "and" must be computed before the "is". Link: https://www.freepascal.org/docs-html/ref/refch12.html Mattias ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] precedence "is" and "and"
Op 2018-12-08 om 20:38 schreef Mattias Gaertner via fpc-pascal: According to the docs, the "is" operator is fourth level, the "and" is second level, so the "and" must be computed before the "is". But it seems fpc treats "is" and "and" as same level: logical (boolean) vs bitwise AND difference? ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] precedence "is" and "and"
On Sat, 8 Dec 2018 21:23:57 +0100 Marco van de Voort wrote: > Op 2018-12-08 om 20:38 schreef Mattias Gaertner via fpc-pascal: > > According to the docs, the "is" operator is fourth level, the "and" > > is second level, so the "and" must be computed before the "is". But > > it seems fpc treats "is" and "and" as same level: > > logical (boolean) vs bitwise AND difference? I don't see where the bitwise should be involved here. There is no integer. The docs do not mention a different precedence lvl for logical/bitwise "and". It does not explain difference between "and" and "or". Mattias ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] precedence "is" and "and"
On Sat, 8 Dec 2018, Mattias Gaertner via fpc-pascal wrote: On Sat, 8 Dec 2018 21:23:57 +0100 Marco van de Voort wrote: Op 2018-12-08 om 20:38 schreef Mattias Gaertner via fpc-pascal: > According to the docs, the "is" operator is fourth level, the "and" > is second level, so the "and" must be computed before the "is". But > it seems fpc treats "is" and "and" as same level: Hm. In delphi, AS is second level, and 'is' is fourth level. http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Expressions_(Delphi) If FPC does this differently, then I think this is an incompatibility. logical (boolean) vs bitwise AND difference? I don't see where the bitwise should be involved here. There is no integer. The docs do not mention a different precedence lvl for logical/bitwise "and". Because to the best of my knowledge, here isn't any difference in precedence, so there is nothing to explain. It does not explain difference between "and" and "or". Of course it does. See section on Logical operators https://www.freepascal.org/docs-html/current/ref/refsu46.html or boolean operators https://www.freepascal.org/docs-html/current/ref/refsu47.html I must confess it assumes that the reader knows what logical 'and' and 'or' means, but someone who does not know that will probably not read the docs. (although, he will also not understand "not" either and maybe read the docs...) Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] precedence "is" and "and"
On Sat, 8 Dec 2018 22:03:11 +0100 (CET) Michael Van Canneyt wrote: >[...] > In delphi, AS is second level, and 'is' is fourth level. > > http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Expressions_(Delphi) > > If FPC does this differently, then I think this is an incompatibility. What has "as" to do with this thread? > >> logical (boolean) vs bitwise AND difference? > > > > I don't see where the bitwise should be involved here. There is no > > integer. > > The docs do not mention a different precedence lvl for > > logical/bitwise "and". > > Because to the best of my knowledge, here isn't any difference in > precedence, so there is nothing to explain. Yes, that's my point. Even if bitwise "and" would play a role here, the precedence would still be the same. > > It does not explain difference between "and" and "or". > > Of course it does. See section on Logical operators > > https://www.freepascal.org/docs-html/current/ref/refsu46.html > > or boolean operators > > https://www.freepascal.org/docs-html/current/ref/refsu47.html I looked at it, but I still don't understand. Perhaps you can explain the examples I gave? // compiles, but should fail: if o is TComponent and b then ; if o is TComponent or b then ; // compiles in fpc, but not in Delphi: if b or o is TComponent then ; // does not compile, correct if b and o is TComponent then ; Mattias ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] precedence "is" and "and"
var b: boolean; o: TObject; begin // this compiles, but should fail: if o is TComponent and b then ; It will compile if $BOOLEVAL is on the default (-) because the result can be determined without considering precedence, see: https://www.freepascal.org/docs-html/prog/progsu4.html Try it the other way round and it will fail: o: TComponent; if o is TObject Martin. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] precedence "is" and "and"
On Sat, 8 Dec 2018, Mattias Gaertner via fpc-pascal wrote: On Sat, 8 Dec 2018 22:03:11 +0100 (CET) Michael Van Canneyt wrote: [...] In delphi, AS is second level, and 'is' is fourth level. http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Expressions_(Delphi) If FPC does this differently, then I think this is an incompatibility. What has "as" to do with this thread? Perhaps FPC treats "is" and "as" on the same level, it would explain the error ? >> logical (boolean) vs bitwise AND difference? > > I don't see where the bitwise should be involved here. There is no > integer. > The docs do not mention a different precedence lvl for > logical/bitwise "and". Because to the best of my knowledge, here isn't any difference in precedence, so there is nothing to explain. Yes, that's my point. Even if bitwise "and" would play a role here, the precedence would still be the same. Agreed. It was Marco who brought this up ? > It does not explain difference between "and" and "or". Of course it does. See section on Logical operators https://www.freepascal.org/docs-html/current/ref/refsu46.html or boolean operators https://www.freepascal.org/docs-html/current/ref/refsu47.html I looked at it, but I still don't understand. Perhaps you can explain the examples I gave? // compiles, but should fail: if o is TComponent and b then ; if o is TComponent or b then ; My hypothesis is that FPC treats 'is' and 'as' on level 2 (contrary to documentation). This is consistent with what you observe. If 'is' is second level (i.e. the same as "as") then that would explain why it compiles, because the 'o is TComponent' will be evaluated first: in the first line because evaluation happens from left to right, in the second line because 'is' takes precedence over 'or'. // compiles in fpc, but not in Delphi: if b or o is TComponent then ; Delphi is consistent with 'is' being on a lover level: "is" is lower level, so b or O is treated first. Again, FPC's behaviour is consistent with treating 'is' on the same level as 'as': because 'is' takes precedence over 'or', you get no error. // does not compile, correct if b and o is TComponent then ; Indeed. (b and O) is evaluated first (left to right) All is consistent with "is" and "as" being on the same level. This is not how delphi does it. So we adapt the documentation, or make the compiler delphi compatible. Given that this has been in the compiler for years, I guess most people use brackets (I know I do) Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
