11 Mar
2025
11 Mar
'25
12:06 a.m.
re yacc vs RD
i agree that they are about the same,
where the edge would tilt based on the parsed language.
BUT when the parsed language (like go) is not yet defined,
yacc is the only option.
On Mon, Mar 10, 2025 at 4:50 PM Clem Cole <clemc(a)ccc.com> wrote:
Marc - check out OpenSIMH( https://opensimh.org)
Check out over 40 different simulators including the I7000 which
supports IBM 701,7010,7070,7080, 7090 - https://opensimh.org/simulators/
ᐧ
On Mon, Mar 10, 2025 at 7:12 PM Marc Rochkind <mrochkind(a)gmail.com> wrote:
This thread started to be about what I thought
were system programming
languages (e.g., C, BLISS) and seems to have meandered into a general
discussion of languages that were around in the 1960s and 1970s, so, what
the heck, I'll add my own story.
PL/0 is an education programming language introduced in the book, *Algorithms
+ Data Structures = Programs*, by Niklaus Wirth in 1976. It's a great
language for teaching compiler writing because it contains interesting
concepts, such as recursive functions, yet isn't overly complicated. I
wrote a PL/0 compiler for the IBM 701 (
https://github.com/MarcRochkind/pl0compiler)
Yeah, that's not a misprint. I wrote perhaps the world's only 701
emulator (https://www.mrochkind.com/mrochkind/a-701.html) and my PL/0
compiler runs on it. Unfortunately, I can't verify that the compiled code
runs on an actual 701, since I'm sure there haven't been any in operation
for many decades. For those of you who haven't had the pleasure,
programming the 701 is really hard. It had no index registers, and the sign
bit didn't participate in shifts. Still, my compiler compiles full-blown
PL/0.
So there! ;-)
Marc Rochkind
On Mon, Mar 10, 2025 at 2:49 PM Bakul Shah via TUHS <tuhs(a)tuhs.org>
wrote:
Perhaps the interviewer was looking for something
dumb like the following
and not a full RD parser?
int count = 0;
while (*cp) {
char c = *cp++;
count += c == '(' ? 1 : c == ')' ? -1 : 0;
if (count < 0) return -1; // FAIL: one too many )
}
if (count > 0) return -1; // FAIL: too many (
return 0; // SUCCESS
Though this will fall apart if you also want to also balance braces &/or
brackets and must catch invalid cases like "(..[..)..]"!
--
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On Mar 10, 2025, at 8:19 AM, John Cowan
<cowan(a)ccil.org> wrote:
I was working at the whiteboard during a job interview once. I had
been asked to
write a function to report if its input had balanced
parentheses. No problem: I wrote an RD parser in Python (which I prefer
for whiteboarding) to detect balance and return True if the parse was
successful and False if EOF was reached.
I was starting to write some tests when the interviewer interrupted me.
"What is that?"
"It's a recursive descent parser. It detects if the input is
well-formed."
Blank look.
I started to walk him through the code.
He interrupted me. "Excuse me, I'll be back in a few minutes."
Long wait, maybe 15-20 minutes. Someone else comes in. "Thank you, the
recruiter will get back to you." That's the last I hear from them.