The naked truth about writing a programming language (2014)

Post by qznc » Sun, May 03, 2020, 6:45 AM UTC

a1369209993 wrote: post #103

billconan wrote: post #2

I want to implement a toy programming language, but I have questions regarding the following in that article: > Context free grammars. What this really means is the code should be parseable without having to look things up in a symbol table. C++ is famously not a context free grammar. A context free grammar, besides making things a lot simpler, means that IDEs can do syntax highlighting without integrating in most of…

Note that "context free grammars", in the technical sense, is completely the wrong thing. Eg, enforcing consistent indentation is not context free: foo() { return; } ↓↓↓↓↓↓↓↓↓↓↓ aaaa{ bbbbreturn; cccc} ↓↓↓↓↓↓↓↓↓↓↓ aaaabbbbcccc This is equivalent to aⁿbⁿcⁿ, which is pretty much the canonical example of a non-context-free language. What you acually want is not context-free grammar, but, as TFA says: > the code should b…

Post by ChicagoDave » Sun, May 03, 2020, 7:16 AM UTC

Post by GreedCtrl » Sun, May 03, 2020, 7:45 AM UTC

pbiggar wrote: post #136

rgbrenner wrote: post #127

Earlier quoted context omitted.

You have a grammar... you're just enforcing the rules when data is entered. The same as if my editor stopped accepting input if I miss typed a line until it was fixed.. or if I was required to select one of it's autocomplete suggestions. let x = 5 "hi " ++ name DB::set{} Are you saying these lines from the video are not consistent throughout? Like in one part I'll type "x = 5" to assign 5 to x, but somewhere else I'l…

I had to look up whether you were technically accurate (I've a PhD in compilers but parsing's not really my thing), and I think the answer is "it depends, maybe?" To get to the root of the issue though, there is not a parser. Well, one could consider the function that takes each keystroke to be a parser - though I don't know if that's technically correct either. So perhaps the more accurate thing to say is there is n…

Post by pjmlp » Sun, May 03, 2020, 7:50 AM UTC

JoeSmithson wrote: post #46

WalterBright wrote: post #29

Earlier quoted context omitted.

My opinion is that Jonathan Blow is an amazing developer and he should be joining us on D! It's been a while since I reviewed the language, and I'd have to re-review it to say anything sane here. But one thing stuck out at me. In D, the support for Compile Time Function Execution (CTFE) is very extensive, and opens the door to a lot of incredible metaprogramming abilities. Jai has this too, but has extended it to all…

I mean, do those people who download and compile code not then generally... run it...? Perhaps I'm missing something but the issue here seems to be whether you trust the source, not whether syscalls are made at compile time or run time?

Post by foldr » Sun, May 03, 2020, 8:38 AM UTC

signaru wrote: post #144

kyllo wrote: post #100

Earlier quoted context omitted.

Context-free has nothing to do with symbol tables, it just means that in the grammar, the left-hand side of a production rule can only have a single non-terminal symbol, which can always be replaced by the expression on the right-hand side, without ambiguity. Language features are an orthogonal issue--you can implement any language feature with a CFG, but you just can't reuse the same keyword or operator to have diff…

In BASIC the equal symbol "=" can mean assignment or equality depending on "context". Is this an example of a non context free? On the other hand, I've seen EBNF definition of BASIC (VB, actually). Is this a contradiction? (just someone still learning)