Re: test program for Extended Pascal strings

14 Nov 2005

      Waldek Hebisch wrote:
...
...
I then get:
actual schema discriminants do not match
in this line:
valueparam(fval,ls2);
Though the text of the message is somewhat misleading, the error
(according to strict EP rules) is correct (i.e., the test is not EP
compliant), as Length (fval) = 14 and Length (ls2) = 7:
: 6.7.3.2 Value parameters
:
: If the parameterÂform of the valueÂparameterÂspecification contains a
: schemaÂname that denotes the schema denoted by the required
: schemaÂidentifier string, then each corresponding actualÂparameter contained
: by the activationÂpoint of an activation shall possess a type having an
: underlyingÂtype that is a stringÂtype or the charÂtype; it shall be an error
: if the values of these underlyingÂtypes, associated with the values denoted
: by the actualÂparameters, do not all have the same length.
I think that GPC is wrong here. Namely, we have:
TYPE  ...
      s20 = string(20);
so s20 does _not_ denote the `string' schema, it is merely a type
produced from that schema with a tuple.
6.7.3.2 applies only for declarations of form:
PROCEDURE valueparam(fst1, fst2: string);
That is clear if you think about intended implementation: for
discriminated schema you pass just the data. For undiscriminated
schema you pass the data and a descriptor. If multiple parameters
have the same type you can pass a single (common) descriptor.
IMHO possibility of such optimization is the only justification
for 6.7.3.2. Of course, our implementation is quite different...
Oh yes, I had misread this case (that's why GPC's error message
appeared strange to me, should have looked closer ...)

This patch fixes this bug, and also a similar one with string
var-parameters, if I understand this case right now (the statement
`p (w^)' in fjf1098b.pas is correct, isn't it?).

{$extended-pascal}

program fjf1098a (Output);

type
  s = String (20);

procedure p (a, b: s);
begin
  WriteLn (a, b)
end;

begin
  p ('OK', '')
end.

{$extended-pascal}

program fjf1098b (Output);

type
  s = String (20);

procedure p (var a: s);
begin
  Write (a)
end;

var
  v: ^s;
  w: ^String;

begin
  New (v);
  v^ := 'O';
  p (v^);
  New (w, 20);
  w^ := 'K';
  p (w^);
  WriteLn
end.

Frank

-- 
Frank Heckenbach, frank@g-n-u.de, http://fjf.gnu.de/, 7977168E
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