Returning a string from a Function (VAX PASCAL)

This is one for the software archaeologists!

And before you ask why was I even bothering to try to get this to work the reason it is simply because I can - which I think is a perfectly good excuse!

I found that the following code for a procedure compiles using VAX PASCAL (and runs as expected)..

PROCEDURE format(number : INTEGER);
   VAR
      result : STRING(16);
   BEGIN
     :
     :
      writeln(result);
   END.

However if turn this into a function and try to return the result as a string it won't compile.

FUNCTION format(number : INTEGER) : STRING(16);
   VAR
      result : STRING(16);
   BEGIN
     :
     :
      format := result;
   END.

The error suggests that the error is at type definition for the function.

FUNCTION format(number : INTEGER) : STRING(16);
                                    1
PASCAL-E-TYPCNTDISCR, Type can not be discriminated in this context

I tried using VARYING and ARRAY types instead of STRING but they don't work either. Unfortunately I can't find an example of a function that returns a STRING in SYS$EXAMPLES or in the manuals I found of bitsavers.

Hopefully someone has a better memory than me.

Thanks

Solution

"Pascal's type system has been described as "too strong", because the size of an array or string is part of its type, ..." Strong and weak typing

This gives a hint that the String(16) in the function return value is too vague for the compiler.

Fix that by declaring a string type that suits the compiler:

type 
  String16 = packed array[1..16] of char;

Then you can use that distinct type in the function:

FUNCTION format(number : INTEGER) : String16;
VAR
  result : String16;
BEGIN
  :
  :
  format := result;
END.

This is very much what was used in many early implementations of the pascal language (and Turbo Pascal), and is still valid. Modern compilers, like Delphi and FreePascal, has implemented a specialized dynamic array for strings, which covers a more convenient handling of the string type, not depending on declaring a strict size.