5 ms·

> an important one for system programming is the possibility to take the address of things which was not possible with original Pascal I believe with (unsafe,

> an important one for system programming is the possibility to take the address of things which was not possible with original Pascal I believe with (unsafe, packed) case variant records you could often get the address of anything that was allocated on the heap: ... type ptrAddr = packed record case Integer of 0: (addr: Integer); 1: (ptr: ^Something); end; var p: ptrAddr; var somethingPtr: ^Something; begin new(somethingPtr); { allocate a Something } p.ptr = somethingPtr; { copy its pointer } writeln('Allocated something at', p.addr); ... (Apologies for any errors - I don't write Pascal very often and haven't tested this.) This obviously relies on implementation-specific behavior such as integers and pointers being the same size. With this sort of trickery you can do all sorts of (unsafe) things including pointer arithmetic, custom memory allocators, garbage collectors, (unsafe) type casts, (unsafe) low-level memory and memory-mapped I/O access, etc..

Rochus 4y ago
There were indeed loopholes in variant records you could misuse for all kinds of tricks, and Wirth was aware of these and finally replaced the concept by type extension. Instead of "not possible" I should better have stated "not officially supported". My point was instead, that Lisa Pascal added concepts, which were official part of the language specification, from which we can conclude, that (also) from the view of Apple original Pascal was not suited for the endeavor. Others came to the same conclusion (see e.g. the famous paper by Kernighan), and even Wirth added features similar to the ones found e.g. in Lisa Pascal to his Modula-2 language.
- musicale 4y ago
  If you want to pick nits, many C and C++ programs and OS kernels also rely on technically undefined and implementation/machine-specific behavior. From which I suppose we can conclude that C/C++ without undefined and/or implementation-specific behavior has been found to be unsuitable for systems programming. Or that systems programs tend to be non-portable by nature. Perhaps a more charitable conclusion is that languages like Wirth Pascal and K&R C (for example) contain (sometimes explicit and intentional) loopholes and unsafe/technically undefined behavior which can be useful for systems programming but problematic for memory safety and security/reliability. Sadly Pascal standardization seems to have stalled after ISO Extended Pascal in 1991, while C is still evolving into C23.
  - Rochus 4y ago
    All languages have loopholes; even Oberon has at least one, in the type case statement (uncovered by C. Szyperski).
- musicale 4y ago
  > from which we can conclude, that (also) from the view of Apple original Pascal was not suited for the endeavor Another conclusion might be that Apple started with UCSD Pascal (which was available for the Apple II and already included extensions to standard Pascal) and that they thought that certain extensions were useful even if they weren't technically necessary. Clearly the Lisa didn't need Clascal or Object Pascal (the Macintosh didn't require them), but they provide advantages in terms of conciseness, modularity, reusability, etc..

Rochus 4y ago

There were indeed loopholes in variant records you could misuse for all kinds of tricks, and Wirth was aware of these and finally replaced the concept by type extension. Instead of "not possible" I should better have stated "not officially supported". My point was instead, that Lisa Pascal added concepts, which were official part of the language specification, from which we can conclude, that (also) from the view of Apple original Pascal was not suited for the endeavor. Others came to the same conclusion (see e.g. the famous paper by Kernighan), and even Wirth added features similar to the ones found e.g. in Lisa Pascal to his Modula-2 language.

musicale 4y ago
If you want to pick nits, many C and C++ programs and OS kernels also rely on technically undefined and implementation/machine-specific behavior. From which I suppose we can conclude that C/C++ without undefined and/or implementation-specific behavior has been found to be unsuitable for systems programming. Or that systems programs tend to be non-portable by nature. Perhaps a more charitable conclusion is that languages like Wirth Pascal and K&R C (for example) contain (sometimes explicit and intentional) loopholes and unsafe/technically undefined behavior which can be useful for systems programming but problematic for memory safety and security/reliability. Sadly Pascal standardization seems to have stalled after ISO Extended Pascal in 1991, while C is still evolving into C23.
- Rochus 4y ago
  All languages have loopholes; even Oberon has at least one, in the type case statement (uncovered by C. Szyperski).
musicale 4y ago
> from which we can conclude, that (also) from the view of Apple original Pascal was not suited for the endeavor Another conclusion might be that Apple started with UCSD Pascal (which was available for the Apple II and already included extensions to standard Pascal) and that they thought that certain extensions were useful even if they weren't technically necessary. Clearly the Lisa didn't need Clascal or Object Pascal (the Macintosh didn't require them), but they provide advantages in terms of conciseness, modularity, reusability, etc..