[palish]

"I'm familiar with parser combinators, but not the Attoparsec or other libraries. Furthermore, I have limited Haskel experience, so I'm struggling to read this. In particular, the use of symbols and overall terseness are hard to get through. I'm also really uncomfortable with the order of operations of all these operators."

This is why I've never identified with "code should comment itself".

I'm not afraid to admit it: I am a dumb programmer. As a dumb programmer, the only way for me to be a good programmer is to be effective.

To be effective, I need to minimize the "time spent understanding code" phase of software development. Furthermore, I will likely be working within a team.

The opposite of that is to be writing "prototype" code --- code which is written to explore the problem space and to gain a better understanding of specific patterns to best accomplish a goal.

But once the prototype phase is over, all of that code is deleted, and is replaced with commented code. (If possible, I try to explain each step of the algorithm in English, first, and then write the code. This is slower, but results in far fewer bugs and a more solid foundation.)

I look at it this way: when my life ends, either I will have gone as far as my own brain was able to take me --- or I will have gone as far as my team's brains were able to take us. I'm willing bet my life that teams of "less brilliant" people are more effective than individuals of excessive brilliance. I write my code accordingly.

-------------------

That said, there is no excuse for laziness. Even if I am merely "competent", it's important for me to strive to be brilliant, even if I'll never attain it.

[ezyang]

In my opinion, this code comments itself, even more so than a manually, written-out parser would.

Here's how I would think about it. What would a grammar for Lisp look like?

    value := list | number | symbol
    list := '(' value + ')'
    number := [0-9]+
    symbol := [A-Za-z-]+

OK, great. Now how do I look at this code?

    value :: Parser Value
    value =
          List <$> (char8 '(' *> sepBy value (takeWhile1 isSpace_w8) <* char8 ')')
      <|> Number . fst . fromJust . B.readInteger <$> takeWhile1 isDigit_w8
      <|> Symbol <$> takeWhile1 (inClass "A-Za-z\\-")

Even if I don't understand the combinators, I can blank them out for now and focus on the recognizable semantic bits. I see List, Number and Symbol, ok, so my guess is that <|> does something like a | might in my grammar, and each line corresponds to a different way a value can be expressed. For list, I see some quoted '(' and ')', so I guess that 'char8' means "match this literal." In fact, I can just read all of that off, and it makes sense. Nevermind what > and < are doing, I'll ignore that for now. And so forth.

Suppose I wanted to make a superficial change, like make $ a recognized symbol in the language. That's super easy. I don't even need to look at the docs. If I want to introduce a new syntactic construct? A little harder; I'll have to go check the attoparsec docs. But you'd have to look up the docs for a library in any language, anyway.

All's not well; in particular, this code conflates the tokenizing and parsing steps (notice that I don't say anything about whitespace in my grammar, but there's some line-noise here dealing with it.) That decreases the readability a little, but you gain efficiency with it.

Maybe there's a tradeoff: the use of a library and symbolic combinators makes it harder to tell precisely how the code manages to actually do any parsing. That's true of any abstraction. But what's really great about this is that I can easily tell what the big picture of the code is. A page or two of state machine would not do that for me!