1 Sep
2017
1 Sep
'17
9:07 p.m.
On 2017-09-01 12:22 PM, Dan Cross wrote:
I'm well aware of that, which is why I specifically mentioned lexical
closures as (one of many) ideas with a powerful effect on expressiveness
and style.
--Toby
On Fri, Sep 1, 2017 at 10:43 AM, Toby Thain
<toby(a)telegraphics.com.au
<mailto:toby@telegraphics.com.au>> wrote:
On 2017-08-31 10:38 PM, Dan Cross wrote:
[snip]
I mean in the mid-80s rewrite, of course.
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?
Maybe Professor Knuth himself has written about that, I'm not sure. A
great question for him, anyhow.
He's in an excellent position to contrast these 3 languages.
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.
[snip]