I finished Let Over Lambda recently. I'm not an experienced lisp programmer but it's strangely readable if you allow yourself to not understand every little detail of the Common Lisp code. For example I hadn't read On Lisp. I had read The Little Schemer.
It's a wonderful tour of advanced macro concepts. With several of the macros presented I found myself saying "well that's just x language feature in y" but that's missing the point. The point is that Common Lisp allows you to implement your own language features, with macros of course!
This chapter is a wonderful climax to the whole book. Lisp moving Forth moving Lisp reminded me of the intertwined nature of DNA, RNA and proteins in Biology.
There's great humour throughout the book, I especially enjoyed the little sideways jabs at Scheme programmers!
Take C#, if you want a new language feature or syntax added you have to propose it to the language design team, they have to decide it's worth implementing then you have to wait on it being implemented and released and your tooling updated.
If I want some new syntax in a LISP, I just write a macro.
e.g. the following threading macro in clojure
(->> x
foo
bar)
Takes x and passes it as the last argument to foo, then the result of foo is passed as the last argument to bar. Alternative you have -> for passing it as the first argument. These are from the standard library, but if they weren't they would be trivial to write yourself.
And no strings involved when you write macros in lisp either. It's just lists, your macro is just building a list. Because the syntax is just lists and there's no difference between lists and the syntax.
AFAICT, actually manipulating the AST, which then in turn allows you to implement your own language features, inserting additional debugging info, memoizing a function by just wrapping it in a macro, or optimizations based on domain knowledge.
all the things, if macro system is sufficiently sophisticated (ie., hygienic with ability to attach metadata to syntax object). Racket is one of languages with such system, and they implemented static typing using them.
It was a mind bending experience, although I quit after a while as the programs were kind of glass sheet quality brittle as they grew.
Sometimes I feel I need to start again to keep my brain from losing thinking skills over time.
It's a wonderful tour of advanced macro concepts. With several of the macros presented I found myself saying "well that's just x language feature in y" but that's missing the point. The point is that Common Lisp allows you to implement your own language features, with macros of course!
This chapter is a wonderful climax to the whole book. Lisp moving Forth moving Lisp reminded me of the intertwined nature of DNA, RNA and proteins in Biology.
There's great humour throughout the book, I especially enjoyed the little sideways jabs at Scheme programmers!
If I want some new syntax in a LISP, I just write a macro.
e.g. the following threading macro in clojure
(->> x foo bar)
Takes x and passes it as the last argument to foo, then the result of foo is passed as the last argument to bar. Alternative you have -> for passing it as the first argument. These are from the standard library, but if they weren't they would be trivial to write yourself.
And no strings involved when you write macros in lisp either. It's just lists, your macro is just building a list. Because the syntax is just lists and there's no difference between lists and the syntax.
Without macros, regular expressions are strings at compile time and then at runtime objects are created based on the strings to evaluate them.
With macros, regular expressions are expanded at compile time into Common Lisp code that implements the evaluation.
There's a similar idea with an ORM library.
Without macros, the object-relational mapping is defined at compile time and any dynamic SQL is generated at run time.
With macros, the object-relational mapping is used at compile time to expand the query macros into Common Lisp code that includes the actual SQL.
Then also remember that the compiler is available at runtime in a lisp, so the distinction only matters when comparing it to non-lisps.