[Oberon] objects and jewels

[Frans-Pieter Vonck]

> Consider the following examples.
> IF ch = 'U' THEN
>   outputProc := WriteToUART
I remember in the module Serial you used procedure types for writing to
the UART0. The LPC2148 has two uarts and I adpted the code in a new module
to use the other UART. Now I understand procedure types are a way to
select the desired IO device. Do I recall correctly that you rewrote
Serial to meet this flexibility?

Greets,
F.P

>> -----Original Message-----
>> From: Frans-Pieter Vonck [mailto:fp at vonck.nl]
>> Sent: Wednesday, 20 February 2013 5:42 AM
>> To: Felix Friedrich
>> Cc: ETH Oberon and related systems
>> Subject: Re: [Oberon] objects and jewels
>>
>> > An attempt to call a non-initialized procedure variable usually
>> > results in a trap.
>> I'm curious, do you think this an code error that should be discovered
>> by
>> the compiler instead of generating a trap at runtime?
>>
>
> No. In most non-trivial cases it is not possible to determine, at the time
> a
> program is compiled, if a procedure variable will have a valid value at
> runtime whenever the procedure variable is called.
>
> Consider the following examples. Apart from the first (which is both legal
> and very useful), all only have a *possibility* that the procedure
> variable
> is initialised, but it is not until runtime that you will know for sure.
>
> ---------------------------------
>
> procVar := NIL;
>
> ---------------------------------
>
> read(ch);
> IF ch = 'U' THEN
>   outputProc := WriteToUART
> ELSIF ch = 'L' THEN
>   outputProc := WriteToLCD
> END;
>
> ---------------------------------
>
> SomeOtherModule.SomeProcedure(procVar);
>
> ---------------------------------
>
> procVar := someOtherProcVar;
>
> ---------------------------------
>
> TYPE
>   ProcType = PROCEDURE(param1, param2: INTEGER);
>   ProcArray = ARRAY 10 OF ProcType;
> VAR
>   p1, p2: ProcArray;
>   param1, param2: INTEGER;
> ...
> ...
> p1 := p2;
> p1[7](param1, param2);
>
> ---------------------------------
>
> etc. etc.
>
>
> Regards,
>
> Chris Burrows
> CFB Software
> Astrobe v4.3 - Oberon for ARM Cortex-M3 Microcontrollers
> http://www.astrobe.com
>
>
>
>
>
>
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