On 07/03/18 05:33, Wolf wrote:
The major shortcoming of this thread, the way I see it, is that the
answer provided explains what the compiler does, but not why the key
authors of Free Pascal have made these choices. What their choices
achieve is a substantial watering-down of what is supposedly Pascal's
most significant paradigm: strong typing. As Jim Lee points out,
strong typing does limit utility - but if utility is first concern, a
weakly typed language such as C would be more appropriate.
When looking at the (partial) disassembly of my little program, we see
to what degree the compiler writers have sacrificed strong typing:
/*a:=1;*
movb $0x1,0x22de87(%rip) # move 1 as single byte into 8 bit
wide variable A
*b:=a*(-1);*
movzbl 0x22de80(%rip),%eax # move A into register %EAX and
convert to 32 bit
neg %rax # negate what is in %EAX
mov %al,0x22de87(%rip) # extract the low 8 bit from %EAX
and store it in variable B
*writeln(b); // result: 255*/
. . .
This was compiled without any optimizations. As you can see, the
brackets are ignored, as is the fact that variables A and B were
supposed to be multiplied. In other words, the compiler has optimized
the code, where it was not supposed to do so. It has also replaced
byte typed values with longint typed values. It has taken my code and
translated it as if I had written
/ var
a: byte;
b: longint;//
//begin
a:=1;
b:=-longint(a); // convert A to a longint and negate it,
then save result in B
writeln( (Lower(b) ); // 'Lower' is a fictional typecast to
denote that I only use the %AL portion of the %EAX register for the result
end./
Which is quite a bit different from what I did program. Sorry if I am
picky here, but this is the type of bug you can expect in software if
you test using examples, and not through rigorous reasoning. And this
is the reason why the original Borland Pascal had range checking
built-in. If you activate it, the compiler does complain, both on my
little program and on Jim's.
But by now, range checking is optional, and Lazarus at least does not
even activate it by default.
But range checking is not the same as type checking, so I regard it as
a crutch, a work-around that needs to be taken because the compiler
does not adhere to (the spirit of) strong typing. And in this sense,
what I submit here represents the same issue as what is given in the
subject string if the whole thread:
Strong typing, and also readability, has been sacrificed on the altar
of utility, by using implicit type conversions.
Maybe we do get some views from the key authors of Free Pascal.
Wolf
I didn't fully understand the intent of your first post, but now I get
what you're saying.
I tend to agree. Strict typing is the main thing that separates Pascal
from C, conceptually. I'd rather not see them converge.
-Jim
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