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That is amazing, well done. I think it deserves more discussion so hopefully I can start some. I've dabbled in Haskell and Lisp but really just touched the sur

That is amazing, well done. I think it deserves more discussion so hopefully I can start some. I've dabbled in Haskell and Lisp but really just touched the surface. My question is how hard was it to do macros with Haskell where I assume it needs to produce code that is strongly typed. If you write a macro that produces a typing error, does it just crash, or return a Err from a Either Program Err? But then you have something that could "crash", because what do you do with that Err. It would be probably impossible to type check a macro in general at compile time (as in the first compilation, not compilations done at runtime), since it has unlimited potential inputs. Other question is how doe this compare to Racket? Did you use Racket to build this?

BalinKing 7y ago
Thank you (sorry for the late reply)! The macro system is not strongly-typed in the sense that Template Haskell is: you can totally use a macro to create invalid Axel code. _However_, the resulting transpiled Haskell code will then fail to compile, so mistakes are still caught at compile-time. (There's no runtime code generation (at least not yet), since all macro expansion happens at compile-time.) I hope this makes sense; I'm not 100% sure what the right terminology is to be honest. You called it, I'm basically just using `Either` for error-handling (well, the equivalent version in the Polysemy library). It's basically like `EitherT`, except IMHO more ergonomic. However, since I'm using the transformer version, I'm just exiting the entire program on an error and printing an error message. Regarding Racket, I hope you don't mind if I quote myself (from https://github.com/axellang/axel/wiki/Why-Axel%3F https://github.com/axellang/axel/wiki/Why-Axel%3F): > Axel was originally inspired by the excellent Hackett project, which adds Haskell's semantics to Racket's syntax and ecosystem. Axel is the "opposite" of Hackett, so to speak, in that it adds Lisp's syntax to Haskell's semantics and ecosystem. Axel tries to make the migration from Haskell as seamless as possible: You can gradually migrate a Haskell project to Axel if that works best for your project; Axel can (soon) auto-convert a Haskell project or file to the corresponding Axel syntax; etc. If you really love Racket (its libraries, hygenic macro system, etc.), however, Hackett's an excellent choice.

BalinKing 7y ago

Thank you (sorry for the late reply)! The macro system is not strongly-typed in the sense that Template Haskell is: you can totally use a macro to create invalid Axel code. _However_, the resulting transpiled Haskell code will then fail to compile, so mistakes are still caught at compile-time. (There's no runtime code generation (at least not yet), since all macro expansion happens at compile-time.) I hope this makes sense; I'm not 100% sure what the right terminology is to be honest. You called it, I'm basically just using `Either` for error-handling (well, the equivalent version in the Polysemy library). It's basically like `EitherT`, except IMHO more ergonomic. However, since I'm using the transformer version, I'm just exiting the entire program on an error and printing an error message. Regarding Racket, I hope you don't mind if I quote myself (from https://github.com/axellang/axel/wiki/Why-Axel%3F https://github.com/axellang/axel/wiki/Why-Axel%3F): > Axel was originally inspired by the excellent Hackett project, which adds Haskell's semantics to Racket's syntax and ecosystem. Axel is the "opposite" of Hackett, so to speak, in that it adds Lisp's syntax to Haskell's semantics and ecosystem. Axel tries to make the migration from Haskell as seamless as possible: You can gradually migrate a Haskell project to Axel if that works best for your project; Axel can (soon) auto-convert a Haskell project or file to the corresponding Axel syntax; etc. If you really love Racket (its libraries, hygenic macro system, etc.), however, Hackett's an excellent choice.