[TUHS] Why Pascal is Not My Favorite Programming Language - Unearthed!

Dan Cross crossd at gmail.com
Sat Sep 2 02:22:20 AEST 2017


On Fri, Sep 1, 2017 at 10:43 AM, Toby Thain <toby at telegraphics.com.au>
wrote:

> On 2017-08-31 10:38 PM, Dan Cross wrote:
> [snip]
> > While most of the
> > languages we use are Turing complete (I suppose that in the limit one
> > can write a Common Lisp implementation in C, for example), it is
> > unarguable that some languages make it *easier* to express some things
> > than other languages. In some cases this is deliberate: consider
> > languages with strong, static type systems versus dynamic but strongly
> > typed languages (or statically but weakly typed). Here the language
> > designers have intentionally made it hard to escape the tyranny of the
> > type system in order to prevent bugs.
>
> (Tyranny is not the word I would use. A more modern viewpoint would
> include topics like parametric polymorphism, typeclasses and so on.)


The specific use of the word "tyranny" was meant to be tongue-in-cheek.
Apologies if it did not come across.

> Anyway, I wonder if Knuth would have produced the same TeX and METAFONT
> > had he started in Pascal; perhaps he would have, but maybe he would have
> > given up on some of the more ambitious parts of both because the
> > language made it much less convenient (not knowing SAIL, I'm
>
> It seems inconceivable to me that there are "ambitious parts" of TeX and
> METAFONT that Professor Knuth had to omit because he was using Pascal.
>

But he wasn't using Pascal. The point was to wonder whether TeX and
METAFONT would be different programs if he were. Clem seemed to imply that
he thought that was unlikely, based on his previous use of SAIL.

[snip]
>
> I have not compared the codebases but wouldn't one expect that the final
> production TeX rewrite is *more* ambitious than the early SAIL version?
> (By the time I began using/porting TeX in the 1980s, the older version
> was completely obsolete.)


I don't know, but that's besides the point: the question was more about how
the initial programming language shaped the design of the program.
Specifically, had Knuth *started* in Pascal instead of SAIL, would TeX have
been different? To put it another way, to what extent was he constrained,
freed, or otherwise influenced by his medium?

> speculating). Perhaps having gone through the exercise of producing TeX
> > in SAIL gave him insight that inspired him to work around Pascal's
> > expressive limitations. Or perhaps the opposite is true.
>
> I honestly don't know what limitations you mean. If you mean "different
> style of expression," sure. (Maybe if SAIL had lexically scoped lambda
> closures, there'd be a difference worth talking about...)


Formally speaking, Pascal is no more limited than any other Turing-complete
language. But there's a difference between *formal* expressiveness and
*informal* expressiveness. Some languages require proportionally more
effort to produce the same program than others. I'm told that sed is
Turing-complete; I'd sure hate to write TeX in it.

The specific "limitations" I'm referring to are mostly covered in the BLTR
#100; things like array length being part of the array object's type; lack
of compile-time initializers, statics, etc.

As an illustrative example, consider the case of a simple dispatch loop
where I want to do some work based on the entry of some string key. In C,
one might write something like this:

typedef struct Cmd Cmd;
struct Cmd {
        const char *cmd;
        int (*thunk)(void);
};

int acmd(void);
int bcmd(void);
// Etc....

Cmd cmds[] = {
    {"a", acmd},
    {"b", bcmd},
    // ...etc...
};

#define nelem(A) (sizeof(A)/sizeof((A)[0]))

int
dispatch(const char *cmd)
{
        for (size_t k = 0; k < nelem(cmds); k++) {
                if (strcmp(cmds[k].cmd, cmd) == 0)
                        return cmds[k].thunk();
        }
        return -1;
}

But how would one write this in Pascal? For a completely unrelated task, I
actually tried to write something like this in Pascal a few weeks ago and
found the lack of compile-time initializers to be an impediment. It struck
me that I could create a record type of some kind or another and
dynamically create a dispatch table via an initialization procedure (say,
building up a linked list or create an array of pointers to functions), but
it struck me that it was possibly more work than just avoiding the
table-driven approach and having a bunch of hard-coded test cases inside of
a loop. Etc.

> Regardless, comparing the work of a Knuth to the industry average is
> > more than a bit unfair. :-)
> >
> >     I suppose Apple's Pascal and Object Pascal -- used for Lisa and
> >     Macintosh applications and systems software -- comes under the "so
> >     people fixed it" category?
> >
> >
> > Object Pascal, Delphi and Free Pascal (which seeks to implement the best
> > of both) seem to have definitely fallen into that category.
>
> I'm not sure if the Apple compiler used circa 1983 was *Object* Pascal
> but it was certainly extended with many intrinsics, casts, and pointer
> operations, bringing it essentially into parity with C for systems and
> application programming.


This confuses me; Apple Pascal and Object Pascal are distinct but related
languages. I specifically referred to Object Pascal, Delphi and Free Pascal
but not Apple Pascal. It strikes me in re-reading what I wrote earlier that
my comments were a bit of a non-sequitur. My bad.

        - Dan C.
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