Re: [BLACKBOX] ARRAY as CONSTANT - ways to express programs

From: [at]} <CFB>
Date: Tue, 12 Feb 2008 12:06:33 +1030

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> -----Original Message-----
> From: BlackBox [mailto:BLACKBOX{([at]})nowhere.xy
> Oleg N. Cher
> Sent: Tuesday, 12 February 2008 9:43 AM
> To: BLACKBOX{([at]})nowhere.xy
> Subject: Re: [BLACKBOX] ARRAY as CONSTANT
>
> Language Oberon was scientific and research project, and
> Component Pascal is industrial solution. If Marc Frei &
> Oberon microsystems crew considered that constant arrays
> are superfluous, we must search a way to express the programs
> by accessible facilities of language. And to work out
> the problems now, instead of tomorrow.
>

Keep in mind that 'constant arrays' are not necessarily 1-dimensional arrays
of simple items. If that were the case an array initialisation feature would
probably have already been implemented. In the general case they can be
multi-dimensional arrays of complex data structures. I suspect that might be
the reason why 'constant arrays are superfluous'.

Can you give an example of the sort of data structures that you are trying
to initialise?

Here is an actual example that might have been implemented using a
structured constant facility (if it had existed) that I was working on just
a couple of months ago. It's written in Modula-2 but the syntax is similar
enough to CP to be understandable.

The application is a Motorola MC68K assembler and I was tackling the problem
of initialising the OpCode data. The original code used a data file which I
wanted to eliminate. The OpCode table is a 1-dimensional array with elements
consisting of a reasonably complex record:

  Table68K : ARRAY [FIRST..LAST] OF TableRecord;

where:

  TableRecord = RECORD
    Mnemonic : TOKEN;
    Op : BITSET;
    AddrModeA : ModeA;
    AddrModeB : ModeB;
  END;

where:

  TOKEN = ARRAY [0..TokenSize] OF CHAR;
  ModeA = SET OF ModeTypeA;
  ModeB = SET OF ModeTypeB;


Using a helper procedure to initialise a single record:

  PROCEDURE Add(Mnemonic : TOKEN; Op : BITSET; AddrModeA : ModeA; AddrModeB
: ModeB);
  VAR
    tr: TableRecord;
  BEGIN
    tr.Mnemonic := Mnemonic;
    tr.Op := Op;
    tr.AddrModeA := AddrModeA;
    tr.AddrModeB := AddrModeB;
    INC(index);
    Table68K[index] := tr
  END Add;

The initialisation code then just became a simple series of procedure calls:

  Add("ABCD", {15, 14, 8}, ModeA{Rx911, RegMem3, Ry02}, ModeB{});
  Add("ADD", {15, 14, 12}, ModeA{OpM68D}, ModeB{EA05y});
  Add("ADDA", {15, 14, 12}, ModeA{OpM68A}, ModeB{EA05a});
  Add("ADDI", {10, 9}, ModeA{}, ModeB{Size67,
EA05e, Exten});
  Add("ADDQ", {14, 12}, ModeA{Data911}, ModeB{Size67,
EA05d});
  ...
  ...

Chris Burrows
CFB Software
http://www.cfbsoftware.com/cp

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Received on Tue Feb 12 2008 - 02:36:33 UTC