Crate fortraith

Compile-Time Compiler That Compiles Forth to Trait Expressions

“We all know Rust’s trait system is Turing complete, so tell me, why aren’t we exploiting this???” - Nathan Corbyn

 #![recursion_limit = "256"]
 #[macro_use] extern crate fortraith;
 use fortraith::*;

 forth!(
     : factorial (n -- n) 1 swap fact0 ;
     : fact0 (n n -- n) dup 1 = if drop else dup rot * swap pred fact0 then ;
     5 factorial
     return type Out as top
 );
 assert_eq!(Out::eval(), 120);

This crate allows the user to exploit traits as much as wanted. It contains around 10% black trait magic, around 40% of the darkest kind of evil macro magic and around 50% of good quality docs (you are here!). Everything is tested and ready for production (a joke).

Although you might not want to really use it in production it serves to show how powerful Rust’s trait system and macro_rules! really are.

If you are new to forth, it is a simple stack-based language. Every operation is done on the stack and grabs and pushes values into it. For example 2 2 + would push 2 to the top of the stack 2 times, take and add them together and push the result back to the stack (So the stack would have only 4 in it if it was empty before pushing the first 2). Its simplicity makes it a usual target for recreational implementation.

See documentation for traits and the macro to see many examples and learn how to use fortraith, and abuse the Rust’s trait system!

“Ok, ok, all that’s fine, but where is my FizzBuzz implementation?” you might ask. Fear not, as tradition dictates FizzBuzz is implemented in fortraith as well.

Macros

forth

Compile forth to trait expressions

Traits

Eval

trait_eval to Rust conversion

and

Logical and two top elements

drop

Remove the top element

dup

Duplicate the top element

eight

( 8 ) Constant number

eq

( = ) Check if two top elements are equal

fact

Calculate the factorial of the top element

falsef

( false ) Constant boolean

fib

Index the fibonacci sequence with the top element

five

( 5 ) Constant number

four

( 4 ) Constant number

iff

( if / else / then ) conditional expression

less

( < ) Check if the second top element is less than the top elements

minus

( - ) Subtract the top element from the second top element

modulo

( % ) Calculate the rest from dividing the second top element by the top element

mult

( * ) Multiply two top elements

nine

( 9 ) Constant number

not

Apply logical not to the top element

one

( 1 ) Constant number

or

Logical or two top elements

plus

( + ) Add two top elements together

pred

Decrement the top element

rot

Rotate three top elements

seven

( 7 ) Constant number

six

( 6 ) Constant number

swap

Swap two top elements

ten

( 10 ) Constant number

three

( 3 ) Constant number

top

Get the top element

truef

( true ) Constant boolean

two

( 2 ) Constant number

zero

( 0 ) Constant number