LCPU is a simple Lisp-like language that compiles to optimized DCPU-16 assembly code. It is a very restricted subset of Lisp. There is no GC, and thus no data structures or run-time closures.
This is intended for usage in Mojang's next game, 0x10c.
- Example program: https://github.com/jlongster/dcpu-lisp/blob/master/examples/print-number.l
- Generated assembly: https://github.com/jlongster/dcpu-lisp/blob/master/examples/print-number.asm
- Watch it run here: http://0x10co.de/imq63
Think of it as a light wrapper around the assembly code, providing named variables, lexically-bound closures, and a little bit of helpful magic here and there.
Create a function like so:
(define (foo x) (+ x 1))
Variable references are statically referenced and compiled out straight to registers. In one function, you are not allowed more variable definitions than there are registers (7, and the 8th is used for the return value).
Nested functions are allowed:
(define (foo x) (define (bar y) (+ x y)) (bar 10))
Run-time closures are not available because of the lack of GC, so the closed function cannot out-live its parent (you can't return
Only 2 kinds of values exist: functions and 16-bit numbers.
There is a lot more we could do to enrich the language but still keep provable semantics statically.
- Named functions and variables
- Nested functions
- Inlinable arithmetic expressions
- Inline assembly
- Small standard library
- Probably other stuff I've forgotten about
Does Not Have
- Garbage Collector
- Run-time closures
- Data types/structures
- Type inference
lcpu script in the
It will print the generated assembly to standard output.
lcpu [-p] [-c1] [-c2] [-c3] [-l] [-e] <program/expression> * -p: print the expanded program * -c1: print the code after the first compilation phase * -c2: print the code after the second compilation phase * -c3: print the code after the third compilation phase * -l: print the code after the linearization phase * -e: run an expression instead of a file
If you get an error, you may have to run this:
touch compiler.ol && make
You can see all the examples in the examples directory.
This code defines
print-number which prints a number to the console:
(define (print color bg-color x y text) (MUL y 32) (ADD y x) (ADD y 0x8000) (SHL color 12) (SHL bg-color 8) (BOR text color) (BOR text bg-color) (SET [y] text)) (define (%print-number n i) (define (p n) (print 0xf 0 (- 31 i) 0 (+ 0x30 n))) (if (< n 10) (p n) (begin (p (% n 10)) (%print-number (/ n 10) (+ i 1))))) (define (print-number n) (%print-number n 0)) (print-number 12345)
Here is the fib program and the resulting assembly code (without the runtime, which just provides a few helpful functions). You can get the full assembly code in examples/fib.asm.
(define (fib a) (if (<= a 1) 1 (+ (fib (- a 1)) (fib (- a 2))))) ;; result will be in register J (fib 8)
JSR global_dash_entry SET PC, __exit :global_dash_entry SET PUSH, return_dash_o1957346 SET PUSH, 0x8 SET PC, global_dash_entry_dash_fib :return_dash_o1957346 SET PC, POP :global_dash_entry_dash_fib SET A, POP SET PUSH, A SET PUSH, return_dash_o3554470 SET PUSH, A SET PUSH, 0x1 SET PC, global_dash__lt__eq_ :return_dash_o3554470 SET A, POP IFE J, 0x0 SET PC, alt_dash_o5960250 SET J, 0x1 SET PC, exit_dash_o9848488 :alt_dash_o5960250 SET PUSH, A SET PUSH, return_dash_o7693500 SET PUSH, A SET PUSH, return_dash_o6022101 SET J, A SUB J, 0x1 SET PUSH, J SET PC, global_dash_entry_dash_fib :return_dash_o6022101 SET A, POP SET PUSH, J SET PUSH, A SET PUSH, return_dash_o8008109 SET J, A SUB J, 0x2 SET PUSH, J SET PC, global_dash_entry_dash_fib :return_dash_o8008109 SET A, POP SET PUSH, J SET PC, _plus_ :return_dash_o7693500 SET A, POP :exit_dash_o9848488 SET PC, POP :__exit SET PC, __exit
You can also view the tests in the
tests directory to see how certain expressions are compiled.
If you want, you can code straight DCPU-16 assembly into your program. For example, here is a function that prints values to the console:
(define (print color bg-color x y text) (MUL y 32) (ADD y x) (ADD y 0x8000) (SHL color 12) (SHL bg-color 8) (BOR text color) (BOR text bg-color) (SET [y] text))
Dereferencing is supported with the normal bracket syntax (i.e.
define-macro is provided for defining macros:
(define-macro (foo t x y) `(begin (define ,t (+ ,x ,y)) (MUL ,t 50))) (foo z 1 2)
is converted into:
(begin (define z (+ 1 2)) (MUL z 50))
This is a powerful construct to make sure you can generate optimized assembly code.
do construct provides iteration. There are two versions of
;; Runs the expression with x starting at 0 and incrementing by 1 ;; until it hits 32 (do (x 0 32) (print (* x 20))) ;; Or you can provide your own start, stepping and stopping ;; expressions. ;; Here x starts as 0, is incremented by 5 and continues looping while ;; x is less than 100 (do (x 0 (+ x 5) (< x 100)) (print x) (print (/ x 2)))
- More optimizations
- A stepping-debugger
There are many more static optimizations we could do. I'm sure there are bugs in this too, as it is rather untested. Please report issues on github if you find any, or contact me at firstname.lastname@example.org.
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