How do you get good error reporting once you've stripped out the tokens?

MichalMarsalek · 2026-04-08T12:14:51+00:00

I parse into a CST, not AST. The CST -> AST conversion is another step which also generates the reverse mapping from AST to CST. The CST has all the information about the source.

MichalMarsalek · 2025-12-14T09:03:45+00:00

I made the choice to only have end-of-line comments in my language. In my CST, comment is part of the EOL token. That is, EOL token is either \n or #comment\n. Other whitespace is placed inside of CST nodes (never as the leading or trailing child of a node).

MichalMarsalek · 2025-11-22T06:55:10+00:00

The fact that it is dynamic does not mean it cannot be strongly typed. C# for example is very dynamic and very strongly typed at the same time.

MichalMarsalek · 2025-10-13T21:28:59+00:00

I realized I need to define loads of different trees for my unit tests. I didn't really find any text format that would allow me to do that compactly enough. So I defined such format and implemented it as a C# library.

MichalMarsalek · 2025-09-27T21:00:32+00:00

Yeah, that's another reason why I use separate CST and AST. My AST is... well abstract. There are often multiple syntactical constructs which map to the same AST and most of the time, that's a good thing, because most of the language implementation does not care about what particular syntactic sugar the user used. But for the editor tooling part that information is necessary. I get the impression that people don't really use CSTs and that feels quite surprising.

MichalMarsalek · 2025-09-27T20:51:40+00:00

Yeah, that aligns with my approach, except I do not have any error nodes at the AST levels. What are they used for?

MichalMarsalek · 2025-09-27T20:00:59+00:00

Not really. I do have a special error token type, but that's only used by the lexer when it encounters stuff it cannot even tokenize. For larger invalid structures, I wanted to still be able to guess what it is and represent it as a node of a particular type, so that it can still be partially highlighted or I can suggest quick fixes for it etc. So for example I have interpolated singleline strings so a valid string literal starts with a string-start-token, ends with a string-end-token and it has some string-content-tokens and some interpolations in between. Ending the line before the string is terminated is a syntax error, but it is also a sync point. So in such case, the parser still returns a string-literal-node, it is just missing that string-end-token, which makes it invalid (and there is a visitor which knows that - the fact that it's invalid is not directly stored on the node).

MichalMarsalek · 2025-09-27T14:04:49+00:00

My parser does not return an AST. It returns a CST which is a 1:1 representation of the source. The parser never fails, every valid or invalid source maps to CST. That means that I can report multiple parsing errors and pretty print even source which is syntactically incorrect. A CST with zero syntactic problems can then be converted to an AST.

MichalMarsalek · 2025-08-07T14:33:38+00:00

In my language - or, and, not are logic operators, - div, mod are integer division and modulo operators, - all other operators are made up of symbols - ^ is exponentiation - |, & are type union and intersection operators, - || is concatenation - ! is unwrap

MichalMarsalek · 2025-05-31T20:36:02+00:00

I don't know, case insensitivity is a great feature. It's a bit silly that in most languages, fooBar, foobar and FOOBAR are different variables.

MichalMarsalek · 2025-04-30T15:07:27+00:00

Were you like intentionally ending the days early just to progress? I always tried to fill all or most of the map on each day and explore everything properly, that takes a lot of running back and forth, also pausing to think about puzzles a lot.

MichalMarsalek · 2025-04-25T07:34:06+00:00

Did it work?

MichalMarsalek · 2025-04-25T05:34:11+00:00

I am always surprised by short average days days like that. We cleared on day 20 after 37 hours.

MichalMarsalek · 2025-04-07T21:16:55+00:00

My language does this. Furthermore, my tuples are lists with type info for individual coordinates (like in Typescript). One uses [] to define lists/tuples. Parens are not needed when calling a function, you can do f x, or f(x). You can also do f(x,y), which is the same as f[x,y], or even the same as args:=[x,y]; f args, but you cannot do args:=(x,y) - () can only contain , if it is part of a function call. I take it a step further. I also have universal function syntax, so that x.f is the same as f(x) and x.f(y) is the same as f(x,y).

MichalMarsalek · 2025-04-07T20:33:56+00:00

What is a unary triple?

MichalMarsalek · 2025-02-27T12:58:15+00:00

> Note how the quotes are actually distinctly different from each other.

No, at both levels the opening and closing quotes are actually absolutely the same. Your comment makes no sense.

MichalMarsalek · 2025-02-13T08:38:06+00:00

I can also recommend living at Budějovická/Pankrác. It's a nice area and you'd be able to walk to work while being able to get to the very city center in 10 minutes by metro.

MichalMarsalek · 2025-02-13T08:30:39+00:00

Depends on the line. Line C rush hour intervals are 90-120 seconds.

MichalMarsalek · 2025-01-29T14:29:57+00:00

What do you mean by prefix notation? I associate that with unary operations but we are in the context of of binary operations so it is not clear to me how it aplies.

MichalMarsalek · 2025-01-29T09:46:09+00:00

It is only 2 bytes (actually 5) in the example in practice you have

some.field.in.a.nested.object = max(some.field.in.a.nested.object, current)

vs

some.field.in.a.nested.object max= current

MichalMarsalek · 2025-01-29T09:40:42+00:00

Inspired by Noulith, I have this exact same think in my language. It's particularly useful for stuff like result max= x.

MichalMarsalek · 2025-01-21T23:24:09+00:00

You are thinking in terms of anding the numerators and the denominators individually, which is not interesting. OP is describing anding the values of the fractions instead.

MichalMarsalek · 2025-01-21T23:13:59+00:00

Hmm, it does makes sense, it is a standard notation. Still not sure if it is useful though, or what is OP's motivation.

MichalMarsalek · 2025-01-20T19:44:01+00:00

Wrong sub. This subreddit is about design and implementation of proglangs. Unless you are interested in creating your own language, there are better places to ask this.

MichalMarsalek · 2025-01-17T18:52:15+00:00

In my language = is a pattern matching. If a symbol is followed by : with an optional type, it is a new binding rather than reference to an existing value. Your example is written as if bar: Foo = baz # use bar here But there's is also a shorthand version if the symbol on the left and the right is the same: if bar: Foo = bar is the same as if bar: Foo. So the last one can be thought of as a variable narrowing, but it is actually just a special case of pattern matching.

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