[Oberon] Syntax details.

[Andreas Pirklbauer]

As per current Oberon-07 language definition, a “designator” consists of an identifier,
which *may* by followed by a “selector”, which - in the case of records - consists
of a dot (“.”) followed by an *identifier*, which however cannot be function call:

  factor       =  ... |  designator [ActualParams]  | ...
  designator   =  qualident {selector}
  selector     =  "." ident | …                             # <—  ident here, and not factor
  ActualParams =  "(" [ExpList] ")"

It would be rather easy to extend to compiler to allow selectors to be a function
call, but it simply is not part of the language definition - and for good reason.
An intermediate variable always works and also makes the code more readable.

-ap


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> There were some 'features' like that in the S3 compiler in the days
> I still wrote commercial Oberon code..
> An intermediate variable always fixed the problem. As in your first example.
> --
> j.
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> > On Sat, Oct 20, 2018 at 3:52 PM <peter at easthope.ca> >wrote: > >In S3 this works.
> >
> >MODULE Test;
> >IMPORT Oberon, Texts, TextFrames, Out, Viewers;
> >VAR
> >nameS: Texts.Scanner;
> >PROCEDURE Test*;
> >VAR
> >v: Viewers.Viewer;
> >BEGIN
> >v := Oberon.MarkedViewer();
> >Texts.OpenScanner(nameS, v.dsc(TextFrames.Frame).text, 0);
> >Texts.Scan(nameS);
> >Out.String("Marked viewer is named ");
> >Out.String(nameS.s); Out.Char("."); Out.Ln
> >END Test;
> >BEGIN
> >END Test.
>
> >Mark the viewer and Test.Test *
>
> >This is more succinct but gives the error "incompatible assignment".
> >Edit.Locate leaves the caret after ().
>
> >MODULE Test IN Oberon;
> >IMPORT Oberon, Texts, TextFrames, Out, Viewers;
> >VAR
> >nameS: Texts.Scanner;
> >PROCEDURE Test*;
> >VAR
> >v: Viewers.Viewer;
> >BEGIN
> >Texts.OpenScanner(nameS,
> >Oberon.MarkedViewer().dsc(TextFrames.Frame).text, 0);
> >Texts.Scan(nameS);
> >Out.String("Marked viewer is named ");
> >Out.String(nameS.s); Out.Char("."); Out.Ln
> >END Test;
> >BEGIN
> >END Test.
>
> >In the Oberon subsystem of A2, the preceeding compiles with no error.
> >Anything interesting to learn from that?
>
> >The (TextFrames.Frame) type cast seems a little devious.
> >Can the result be accomplished without a type cast?
>
> >Thanks, ... Lyall E.
>