sulami / losp

Working (vaguely) through

Losp

In this repo, I'm working through the second half of Crafting Interpreters, the part that is about compiling and running bytecode.

I'm using the book more as an inspiration than a guide, so not only am I working in Rust instead of C (for learning purposes), but I am also implementing a different grammar (for aesthetic purposes). I'm going to be building a Lisp, assuming everything works out.

Note that this is my first ever Rust code, so it's probably terrible all-around. Also, it's not actually very fast, because it's copying around a lot of data rather needlessly.

Usage

If none of the above deterred you and you actually want to run this, here is how:

# Build with
rustc -O losp.rs

No external dependencies, no cargo.

$ ./losp # gives you a nice help print
usage:
losp repl         - start repl
losp depl         - start debug repl
losp run <file>   - run file
losp debug <file> - debug file

The debug print out bytecode as it's being run, which can be a lot if you're using functions or loop, so be advised.

The losp syntax is vaguely Scheme-inspired, with a dash of Clojure:

; comments are from semicolons to the end of the line
; whitespace is ignored

; data types
nil     ; nil
true    ; booleans
3       ; 64-bit integers
.3      ; 64-bit floats
"3"     ; strings
foo     ; symbols
; techically functions are first class, but there is nothing useful
; you can do with them at this point
; there are also no lists, which is a bit ironic

; global variables with `def`
(def pi 3.14159)

; local variables with `let`
; scoping is lexical
(let ((a 1)
      (b 2))
  (+ a b))

; branching with `if` and `when`
(if false
  nil
  (when true
    (print "`when` has an implicit `do` block")
    4))

; `do` allows chaining of operations
(do (print "first")
    (print "second"))

; functions use `defn`, and have an implicit `do` block
; no TCO at this point
; arity is checked at call-time
(defn foo (a b)
  (+ a b))

; there is a `while` loop, not that it's very useful
; they also have an implicit `do` block
(def i 0)
(while (< i 10)
  (def i (+ i 1)))

; equality is by value, the following is true
(let ((a 1)
       b 1)
  (= a b))

; numbers are weakly typed, the following returns 1.1
(+ 1 .1)
(/ 2.2 2)

; no explicit type casts exist

; `print` always prints a trailing newline

You can see the included test file (in Losp) for more usage examples.