[TUHS] Re: What would early alternatives to C have been?

[John Cowan <cowan@ccil.org>]

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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.

On Mon, Mar 10, 2025, 12:10 AM Rob Pike <robpike@gmail.com> wrote:

> A rare case where I disagree with you, Doug. If the language is reasonably
> regular (I do not mean in the strict Kleene sense), a recursive descent
> parser is not much harder to write than a yacc grammar, and much smoother
> at providing good error messages. Having done many yaccs and many RD
> parsers, I no longer go to yacc.
>
> To put it another way, there are few programming tasks I enjoy more than
> writing a recursive descent parser for a sane language.
>
> Now if the language is not so regular, my position might shift. I do
> recall Bjarne dynamically editing the generated tables mid-parse to get
> yacc to handle at least one stage of C++'s development.
>
> Another way to think of it is that if you are designing the language and
> it is undergoing frequent changes in grammar, yacc could certainly be move
> you along faster. But even then once things had settled I'd still redo it
> as RD, for the quality of the result.
>
> You can credit Stephen R. "Software" Steve for this change in my thinking.
>
> -rob
>
>
> On Mon, Mar 10, 2025 at 1:12 PM Douglas McIlroy <
> douglas.mcilroy@dartmouth.edu> wrote:
>
>> > everyone should write for their first compiler in Pascal for a
>> > simple language and no cheating using YACC.  You need to write the whole
>> > thing if you want to understand how parsing really works.
>>
>> Yacc certainly makes it easier to write parsers for big grammars, but
>> it's far from cheating. You need to know a lot more about parsing to use
>> Yacc than you need to roll your own.
>>
>> Hand parsing of a tiny grammar is almost a  necessary step on the way to
>> understanding Yacc. But I think hand-building the whole parser for a
>> compiler is unnecessary torture--like doing trigonometry with log tables.
>>
>> Doug
>>
>

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