[Oberon] FPGA - Simple OOP example

Tomas Kral thomas.kral at email.cz
Thu Aug 16 16:26:37 CEST 2018

On Thu, 16 Aug 2018 14:11:27 +0200
Tomas Kral <thomas.kral at email.cz> wrote:

> 1) Space: m^ = methods^
> vs
> 2) Consistency m = methods

Hi, after much advice from Joerg, I wish to post a revised OOP
example, so you can have a go, too. I managed to hide `VAR W:
Texts.Writer' in the base Term type (class). Example hopefully
demonstrates calling `base' vs `overriden' methods. The fact Oberon-07
exports read only VARs leaves some room for tinkering, simplifying the
code further.

MODULE Term; (* TK 16.8.2018 revised OOP example *)
  IMPORT Texts, Oberon;

    Term* = POINTER TO TDesc;
    Methods* = POINTER TO MDesc;

    (* Base method suite *)
    MDesc* = RECORD
      Write*: PROCEDURE(t: Term; ch: CHAR);
      Refresh*: PROCEDURE(t: Term);
      Ln*: PROCEDURE(t: Term)
      (* other methods come here *)
    END ;

    (* Base data suite *)
    TDesc* = RECORD
      do*: Methods;
      (* generic terminal data comes here *)
    END ;

  VAR W: Texts.Writer; methods: Methods;

  (* ------ Initialisation for clients ------ *)

  PROCEDURE Init*(t: Term);
  BEGIN t.do := methods
  END Init;

  PROCEDURE Clone*(VAR m: Methods);
  BEGIN m^ := methods^
  END Clone;

  PROCEDURE Get*(VAR m: Methods);
  BEGIN m := methods
  END Get;

  (* ------ Term base methods ----- *)

  PROCEDURE Write(t: Term; ch: CHAR);
  BEGIN Texts.Write(W, ch)
  END Write;

  PROCEDURE Refresh(t: Term);
  BEGIN Texts.Append(Oberon.Log, W.buf)
  END Refresh;

  PROCEDURE Ln(t: Term);
  BEGIN Texts.WriteLn(W)
  END Ln;
BEGIN Texts.OpenWriter(W); NEW(methods); methods.Write := Write;
  methods.Refresh := Refresh; methods.Ln := Ln END Term.

  IMPORT Term;

    CapTerm* = POINTER TO CTDesc;
    CTDesc* = RECORD (Term.TDesc)
      (* specific cap terminal data comes here *)
      col: INTEGER 
    END ;
  VAR self, super: Term.Methods;

  PROCEDURE Init*(t: CapTerm; color: INTEGER (* other data for the
  CapTerm if any *) ); BEGIN t.do := self; t.col := color
  END Init;

    VAR up: CHAR;
    IF (ch >= "a") OR (ch <= "z") THEN
      up := CHR(ORD(ch) + ORD("A") - ORD("a"))
    ELSE up := ch END

  (* --------- Methods to override from Term base ------- *)

  PROCEDURE Write(t: Term.Term; ch: CHAR);
  (* Write method specific for CapTerm *)
    ch := CAP(ch); super.Write(t, ch) (* upcalls base Term.Write() *)
  END Write;

  (* Refresh() method not to be overriden *)
  (* Ln() method not to be overriden *)

BEGIN NEW(self); Term.Clone(self); Term.Get(super); self.Write := Write
END CapTerm.

MODULE TestTerm;
  IMPORT Texts, Term, CapTerm, Oberon;

  VAR t: Term.Term; c: CapTerm.CapTerm;

    VAR S: Texts.Scanner;
    Texts.OpenScanner(S, Oberon.Par.text, Oberon.Par.pos);
  Texts.Scan(S); WHILE S.class = Texts.Name DO
      t.do.Write(t, S.s[0]); t.do.Refresh(t); 
      c.do.Write(c, S.s[0]); c.do.Refresh(c); (* calls Term.Refresh() *)
    END ;
    c.do.Ln(t); t.do.Ln(t); c.do.Refresh(c) (* calls Term.Ln() twice *)
  END Run;

BEGIN NEW(t); Term.Init(t); NEW(c); CapTerm.Init(c, 20)
END TestTerm.

TestTerm.Run  a b c ~

Tomas Kral <thomas.kral at email.cz>

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