[Oberon] Fwd: Re: Re: Question about Oberon semantics of VAR parameters

[Jörg]

Hi

A little bit of history:
In the previous language report, chapter 12 explained that rule
https://inf.ethz.ch/personal/wirth/Oberon/Oberon.Report.pdf 
You had to use SYSTEM.BYTE to enable it.
SYSTEM.BYTE disappeared, but the (now undocumented) rule is still there.

Br
Jörg

> Am 07.12.2019 um 09:32 schrieb Jörg <joerg.straube at iaeth.ch>:
> 
> In procedure ORP.Parameter() you find:
> ELSIF (par.type.form = ORB.Array) & (par.type.base = ORB.byteType) & (par.type.len >= 0) & (par.type.size = x.type.size) THEN
> Jörg
> 
>>> Am 07.12.2019 um 09:21 schrieb Jörg <joerg.straube at iaeth.ch>:
>>> 
>> ARRAY N OF BYTE is compatible to anything as long as the size matches.
>> This comes in handy for low level programming.
>> Jörg
>> 
>>>> Am 07.12.2019 um 08:51 schrieb Luca Boasso <luke.boasso at gmail.com>:
>>>> 
>>> 
>>> To the best of my knowledge, that undocumented feature is the only (intentionally) missing type rule in my document.
>>> The type system described is a slight superset of the one implement by the original Oberon-07 RISC compiler.
>>> Let me know if you need clarifications on the document. 
>>> 
>>> oberonc implements all the rules of that document. You can find comments in the source code referring to the type rules, for example in https://github.com/lboasso/oberonc/blob/master/src/OJP.Mod at line 216:
>>>   (* Type Rule A, B *)
>>>   PROCEDURE EqualTypes(t0, t1: OJB.Type): BOOLEAN;
>>>   BEGIN
>>> 
>>> 
>>>> On Fri, Dec 6, 2019, 19:05 rochus.keller at bluewin.ch <rochus.keller at bluewin.ch> wrote:
>>>> Ok, I see, thank you very much.
>>>> 
>>>>  It should be officially documented in any case. I'm implementing my first true Oberon validator by just following the language report word by word and got tons of inexplicable errors because of rule simply not describe there (neither in the tutorial). If I want to be able to successfully parse the Oberon System (which seems like an obligatory test case) then I consequently have to implement these specialities as well. I'm not very good at reading Oberon source code (yet) though, so I would prefer a precise and complete language report. Your document is already more precise, as it seems.
>>>> 
>>>> Best
>>>> R.
>>>> 
>>>> _______________________________
>>>> From: Luca Boasso
>>>> Sent on: Sat, 07 Dec 2019 03:02:01 +0100
>>>> To: rochus.keller at bluewin.ch
>>>> Cc: 
>>>> Subject: Re: [Oberon] Fwd: Re: Re: Question about Oberon semantics of VAR parameters
>>>> 
>>>> Those particular examples exploit an undocumented loophole in the type system that simplify the writing of lower lever functions. I left that out of my document.
>>>> 
>>>> 
>>>> See ORP.Parameter:
>>>> ELSIF (par.type.form = ORB.Array) & (par.type.base = ORB.byteType) & 
>>>>           (par.type.len >= 0) & (par.type.size = x.type.size) THEN
>>>>         ORG.VarParam(x, par.type)
>>>> 
>>>> 
>>>> 
>>>> 
>>>> On Fri, Dec 6, 2019, 17:45 rochus.keller at bluewin.ch <rochus.keller at bluewin.ch> wrote:
>>>> 
>>>> This is a very helpful document indeed, thank you very much. 
>>>> 
>>>> But as it seems it doesn't explain my originally intended examples, e.g FileDir.Mod line 61 or Files.Mod line 104 (the first reported one was unfortunately my mishap, sorry).
>>>> 
>>>> Best
>>>> R.
>>>> --
>>>> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
>>>> https://lists.inf.ethz.ch/mailman/listinfo/oberon
>>> --
>>> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
>>> https://lists.inf.ethz.ch/mailman/listinfo/oberon
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