drafting-interpreters

This is the repository where I keep all the projects I wrote while reading the excellent Crafting Interpreters by Bob Nystrom.

While the interpreters are written in D, I kept the original names.

jlox

Mostly straightforward translation from the book. The code was written while I was a D beginner and the goal was only to practice while reading Part II, so you shouldn't expect idiomatic code.

How to build & run

cd jlox
dub build
./jlox a_lox_source_file # interprets the contents of the file
./jlox # opens an interactive prompt (CTRL-C to quit)

Of note

jlox/expr.d and util/codegen.d (Chapter 5)

Rather than generating the AST types from an external program, I chose to use the metaprogramming facilities of D, in particular string mixins and CTFE.

It is interesting that the code is basically identical to the one I would have written for the external generator.

jlox/ast_printer.d (Chapter 5)

This went through several iterations. I first tried to copy the visitor pattern from the book, only to find out that in D you can't derive from template functions (caveat emptor, I might be wrong.)

I then reimplemented Expr as a std.variant.Algebraic alias and used std.variant.visit to implement the printer.

Algebraic was satisfying but as it so happens I watched the next day Jean-Louis Leroy's presentation at DConf 2018 and decided to try his openmethods instead.

jlox/interpreter.d (Chapter 7)

I had some fun using a static foreach to generate at compile-time case statements for a long and boring switch. I also played with an alias with lambda syntax and wrote a bit more unittests than usual.

To Be Continued

This is a work in progress but I'm regularly working through the book.