4 ms·

Once you have an intuition, you can use yacc.

by 29athrowaway 3y ago

laxd 3y ago
And lose touch with your code and having too deal with problems through a heavily abstracted layer. Great!
- 29athrowaway 3y ago
  You will likely not get a perfect syntax right away. So you will need to iterate on it until you are happy with how it looks and feels, and doing it while developing the compiler yourself will naturally lead to a lot of unnecessary bugs and tech debt. Alternatively, you iterate using a cheaper method and once you reach a point in which you are content with the syntax, you can consider writing a compiler for it. You can also avoid iterating on the syntax so you can ship a compiler as fast as possible, but users won't like the syntax and won't use your language.
  - mcluck 3y ago
    I have a feeling you haven't worked on parsers or compilers that much if you think you design all of the syntax before building anything
- remexre 3y ago
  I don't really think of yacc as having much more abstraction than a regex engine -- like in an (NFA-based) regex engine, you're building a big data structure a human wouldn't want to hand-engineer from a declarative specification. (And, like in regexes, you've got good theory backing it.)
  - laxd 3y ago
    You got good theory backing hand-written parsers, and the code is there right in your face. I don't know how a regex engine works.
    - remexre 3y ago
      By "good theory," I mean being able to know properties of the parser as a result of the formalism. For example, one can prove that any yacc-generated parser never infinite loops and runs in O(n) (at least for the actual parsing; you can write custom code in actions that runs when a construct has been parsed, and of course you can write whatever you want there). If you hand-write a grammar like the following, you'll end up with an infinite loop without restructuring the grammar; such restructuring is of course much easier if you have written the grammar out, rather than having it implicitly exist in code. Expr ::= Expr '[' Expr ']' Expr ::= Name Expr ::= Int If you try to naively parse the following, you'll never parse the marked production either. Something like yacc will warn you about this, while an ordinary compiler compiling a hand-written parser won't. Stmt ::= Expr ';' Stmt ::= Name '=' Expr ';' Stmt ::= Expr '[' Expr ']' '=' Expr ';' Expr ::= Expr '[' Expr ']' Expr ::= Name Expr ::= Int [0] is a good introduction to regex matching, [1] is a good introduction to the algorithm yacc uses, if you want to learn either. [0]: https://swtch.com/~rsc/regexp/regexp1.html https://swtch.com/~rsc/regexp/regexp1.html [1]: https://web.archive.org/web/20210507215636/http://web.cs.dal.ca:80/~sjackson/lalr1.html https://web.archive.org/web/20210507215636/http://web.cs.dal...
      - laxd 3y ago
        > For example, one can prove that any yacc-generated parser never infinite loops and runs in O(n) Trivial when actually writing the code. And your example of infinite left recursion is basics in parser theory. No one in their right mind would write a hanging program like that, at least not for long.
        remexre 3y ago
        Left recursion is basic, sure, but it's not a problem for an (LA)LR parser generator like yacc. (Depending on your parse actions, you might even get slightly better memory consumption when using left recursion rather than right recursion.)
3cats-in-a-coat 3y ago
Once you have an intuition, you just write the parser yourself. I'm not a fan of parser generators. I find them restrictive. It is also notable most mainstream languages do not use tools like YACC, they have "handmade" parsers and compilers. This may seem like I'm suggesting pie-in-the-sky approach from the ground up for something that may never need such control. Could be. But I don't feel like learning YACC is easier than learning how to parse anything in general. I think YACC and so on are holding people back from truly expressing themselves with custom languages, and after all that was the whole point of them writing a language or wasn't it?
- 29athrowaway 3y ago
  So let's say, you decide to create your own programming language, now you can automatically afford to do as much work as the organizations behind mainstream programming languages? Organizations with thousands of contributors, funding, etc.? Now, let's omit that for a moment. Let's say that after having implemented your language after years of work, now for some reason you got 1 prospect user. That person will ask you about: syntax highlighting, linting, code navigation, testing, packaging, documentation, operating systems/architecture support, etc. Who is going to contribute all that if you are busy writing everything by hand? Unless you have as much time as Terry Davis, you are better off starting by piggybacking on something that exists. Then, once you have an idea that scales, you can convince other people to help you and have a successful project. Then you can have a viable ecosystem that people can comfortably join.
  - jstimpfle 3y ago
    The real problem about parsing is not parsing the formal grammar. It's deciding what to store about the parsed input (CST to AST) and designing the ancillary datastructures for further processing, integrating the parser with the rest of the application, etc. The real problem about building a compiler is everything else but not parsing. Parsing is the easiest part. Once you've written a view recursive descent parsers you will probably agree. The parser for syntax highlighting is probably a different one than the parser for AST generation and compilation. So is a parser for batch compilation different to one for incremental compilation. Even the syntax might be different.
miguelgrinberg 3y ago
Knowing how to build a parser manually will make you much much better at generating, and most importantly debugging, automatically generated parsers.
- 29athrowaway 3y ago
  Yes. And once you are done learning every aspect of it, one day you will look yourself in the mirror and you will be 60 years old.
  - benj111 3y ago
    Why do you think people are writing toy programming languages? It's a learning exercise. Sure, if you want to learn to use yacc, or whatever, use yacc. I don't think time efficiency is a useful metric when the overwhelming majority of people is this space aren't doing it for their job, or even because they 'need' to create a new language. Ultimately you could just use python, it'll be faster and more fully featured.
  - furyofantares 3y ago
    I'm not sure why this intuition is so strong, I had it myself before learning this stuff in my early 20s on shipping projects (both existing, and from scratch) and at the end of that I was still in my early 20s. Despite this intuition it's all actually very learnable and my experience is that using a parser generator makes no sense in a professional context and very little sense in a hobby/toy project context.
  - PixyMisa 3y ago
    With any luck that will happen to you sooner or later. Better to have it happen knowing you've mastered some subject.

Once you have an intuition, you can use yacc.

laxd 3y ago

And lose touch with your code and having too deal with problems through a heavily abstracted layer. Great!

29athrowaway 3y ago
You will likely not get a perfect syntax right away. So you will need to iterate on it until you are happy with how it looks and feels, and doing it while developing the compiler yourself will naturally lead to a lot of unnecessary bugs and tech debt. Alternatively, you iterate using a cheaper method and once you reach a point in which you are content with the syntax, you can consider writing a compiler for it. You can also avoid iterating on the syntax so you can ship a compiler as fast as possible, but users won't like the syntax and won't use your language.
- mcluck 3y ago
  I have a feeling you haven't worked on parsers or compilers that much if you think you design all of the syntax before building anything
remexre 3y ago
I don't really think of yacc as having much more abstraction than a regex engine -- like in an (NFA-based) regex engine, you're building a big data structure a human wouldn't want to hand-engineer from a declarative specification. (And, like in regexes, you've got good theory backing it.)
- laxd 3y ago
  You got good theory backing hand-written parsers, and the code is there right in your face. I don't know how a regex engine works.
  - remexre 3y ago
    By "good theory," I mean being able to know properties of the parser as a result of the formalism. For example, one can prove that any yacc-generated parser never infinite loops and runs in O(n) (at least for the actual parsing; you can write custom code in actions that runs when a construct has been parsed, and of course you can write whatever you want there). If you hand-write a grammar like the following, you'll end up with an infinite loop without restructuring the grammar; such restructuring is of course much easier if you have written the grammar out, rather than having it implicitly exist in code. Expr ::= Expr '[' Expr ']' Expr ::= Name Expr ::= Int If you try to naively parse the following, you'll never parse the marked production either. Something like yacc will warn you about this, while an ordinary compiler compiling a hand-written parser won't. Stmt ::= Expr ';' Stmt ::= Name '=' Expr ';' Stmt ::= Expr '[' Expr ']' '=' Expr ';' Expr ::= Expr '[' Expr ']' Expr ::= Name Expr ::= Int [0] is a good introduction to regex matching, [1] is a good introduction to the algorithm yacc uses, if you want to learn either. [0]: https://swtch.com/~rsc/regexp/regexp1.html https://swtch.com/~rsc/regexp/regexp1.html [1]: https://web.archive.org/web/20210507215636/http://web.cs.dal.ca:80/~sjackson/lalr1.html https://web.archive.org/web/20210507215636/http://web.cs.dal...
    - laxd 3y ago
      > For example, one can prove that any yacc-generated parser never infinite loops and runs in O(n) Trivial when actually writing the code. And your example of infinite left recursion is basics in parser theory. No one in their right mind would write a hanging program like that, at least not for long.
      - remexre 3y ago
        Left recursion is basic, sure, but it's not a problem for an (LA)LR parser generator like yacc. (Depending on your parse actions, you might even get slightly better memory consumption when using left recursion rather than right recursion.)

3cats-in-a-coat 3y ago

Once you have an intuition, you just write the parser yourself. I'm not a fan of parser generators. I find them restrictive. It is also notable most mainstream languages do not use tools like YACC, they have "handmade" parsers and compilers. This may seem like I'm suggesting pie-in-the-sky approach from the ground up for something that may never need such control. Could be. But I don't feel like learning YACC is easier than learning how to parse anything in general. I think YACC and so on are holding people back from truly expressing themselves with custom languages, and after all that was the whole point of them writing a language or wasn't it?

29athrowaway 3y ago
So let's say, you decide to create your own programming language, now you can automatically afford to do as much work as the organizations behind mainstream programming languages? Organizations with thousands of contributors, funding, etc.? Now, let's omit that for a moment. Let's say that after having implemented your language after years of work, now for some reason you got 1 prospect user. That person will ask you about: syntax highlighting, linting, code navigation, testing, packaging, documentation, operating systems/architecture support, etc. Who is going to contribute all that if you are busy writing everything by hand? Unless you have as much time as Terry Davis, you are better off starting by piggybacking on something that exists. Then, once you have an idea that scales, you can convince other people to help you and have a successful project. Then you can have a viable ecosystem that people can comfortably join.
- jstimpfle 3y ago
  The real problem about parsing is not parsing the formal grammar. It's deciding what to store about the parsed input (CST to AST) and designing the ancillary datastructures for further processing, integrating the parser with the rest of the application, etc. The real problem about building a compiler is everything else but not parsing. Parsing is the easiest part. Once you've written a view recursive descent parsers you will probably agree. The parser for syntax highlighting is probably a different one than the parser for AST generation and compilation. So is a parser for batch compilation different to one for incremental compilation. Even the syntax might be different.

miguelgrinberg 3y ago

Knowing how to build a parser manually will make you much much better at generating, and most importantly debugging, automatically generated parsers.

29athrowaway 3y ago
Yes. And once you are done learning every aspect of it, one day you will look yourself in the mirror and you will be 60 years old.
- benj111 3y ago
  Why do you think people are writing toy programming languages? It's a learning exercise. Sure, if you want to learn to use yacc, or whatever, use yacc. I don't think time efficiency is a useful metric when the overwhelming majority of people is this space aren't doing it for their job, or even because they 'need' to create a new language. Ultimately you could just use python, it'll be faster and more fully featured.
- furyofantares 3y ago
  I'm not sure why this intuition is so strong, I had it myself before learning this stuff in my early 20s on shipping projects (both existing, and from scratch) and at the end of that I was still in my early 20s. Despite this intuition it's all actually very learnable and my experience is that using a parser generator makes no sense in a professional context and very little sense in a hobby/toy project context.
- PixyMisa 3y ago
  With any luck that will happen to you sooner or later. Better to have it happen knowing you've mastered some subject.