A road to Lisp: Why Lisp
scotto.me
A road to Lisp: Why Lisp
1–10 of 322 posts
Re: A road to Lisp: Why Lisp
#2The website seems to have a bug with syntax highlighting. Pieces of code included in the post text are black, you can still see the actual text if you select it with your mouse. Same bug on Chrome desktop and on Safari on iPad
Re: A road to Lisp: Why Lisp
#3The website seems to have a bug with syntax highlighting. Pieces of code included in the post text are black, you can still see the actual text if you select it with your mouse. Same bug on Chrome desktop and on Safari on iPad
metoo
Re: A road to Lisp: Why Lisp
#4I must admit - I still don't understand macros. I get that they're code that's generated at compile time. But I don't understand how that's different than a function which evaluates other functions. I guess the latter would actually be evaluated at runtime? I think I get it conceptually but I'm not sure I have the muscle memory to reach for them. Anybody here have an "ah hah!" Moment with macros?
Re: A road to Lisp: Why Lisp
#5I must admit - I still don't understand macros. I get that they're code that's generated at compile time. But I don't understand how that's different than a function which evaluates other functions. I guess the latter would actually be evaluated at runtime? I think I get it conceptually but I'm not sure I have the muscle memory to reach for them. Anybody here have an "ah hah!" Moment with macros?
There's a bit of a mental model flip to make maybe.
> they're code that's generated at compile time
They're code that generates code at compile time. Macros can actively walk the AST of the parameters they process and rewrite them completely into new shapes. That transformed AST is what then actually gets compiled.
Re: A road to Lisp: Why Lisp
#6I must admit - I still don't understand macros. I get that they're code that's generated at compile time. But I don't understand how that's different than a function which evaluates other functions. I guess the latter would actually be evaluated at runtime? I think I get it conceptually but I'm not sure I have the muscle memory to reach for them. Anybody here have an "ah hah!" Moment with macros?
Sure, macros are functions that take functions as input, and produce new functions as output. But they take the function's symbols as input and produce a new set of symbols. So a macro can extend the syntax of the language without having to modify the core language system. Anyway, what's unique about Lisp macros vs say, Rust macros, or C style preprocessors, is "homoiconicity". The data structure that a Lisp macro takes as an input, the lisp code, is the same data structure that the language uses normally (S-expressions, lists...), so writing a macro requires few new language skills compared to writing normal lisp (again, compare writing Rust macros, a dark art in comparison).
Re: A road to Lisp: Why Lisp
#7I must admit - I still don't understand macros. I get that they're code that's generated at compile time. But I don't understand how that's different than a function which evaluates other functions. I guess the latter would actually be evaluated at runtime? I think I get it conceptually but I'm not sure I have the muscle memory to reach for them. Anybody here have an "ah hah!" Moment with macros?
[dead]
Re: A road to Lisp: Why Lisp
#8I must admit - I still don't understand macros. I get that they're code that's generated at compile time. But I don't understand how that's different than a function which evaluates other functions. I guess the latter would actually be evaluated at runtime? I think I get it conceptually but I'm not sure I have the muscle memory to reach for them. Anybody here have an "ah hah!" Moment with macros?
You could use them to:
1. Come up with an algorithm to define an algorithm.
2. Code expansion. Instead of typing out 1000 classes that are best represented as a template of a single class, you can define a macro then use it.
3. C++ at least uses them to provide generics.
4. They let you peel back the layers of abstraction to use the language itself as an API. Useful if you want to write static analysis to do analysis on code quality, security, linting, etc.
5. Anything you can imagine, it's metaprogramming.
Re: A road to Lisp: Why Lisp
#9The website seems to have a bug with syntax highlighting. Pieces of code included in the post text are black, you can still see the actual text if you select it with your mouse. Same bug on Chrome desktop and on Safari on iPad
My first thought was that the article was redacted lol
Re: A road to Lisp: Why Lisp
#10All roads lead to Lisp