A purely functional Befunge-93 interpreter, written in final tagless style. Showcasing the beauty and power of compositional design.
Given a Befunge-93 program, usually expressed as a multiline string
val helloWorld =
"""
> v
v ,,,,,"Hello"<
>48*, v
v,,,,,,"World!"<
>25*,@
"""you can run it to completion by calling befunge.run(helloWorld), or
step through it in debug mode with befunge.debug(helloWorld). Note
that both return a cats.effect.IO], which describes their behaviour
in a purely functional manner. You can compose the IO computations
in a larger program, or, if you want to actually trigger their
execution because you are in main or in the repl, call
.unsafeRunSync on them.
The befunge object also contains some example programs for you to
try out.
Befunge-93 is a stack-based, reflective, bidimensional esoteric programming language. The spec is here
A short table of the commands is as follows:
COMMAND INITIAL STACK (bot->top)RESULT (STACK)
------- ------------- -----------------
+ (add) <value1> <value2> <value1 + value2>
- (subtract) <value1> <value2> <value1 - value2>
* (multiply) <value1> <value2> <value1 * value2>
/ (divide) <value1> <value2> <value1 / value2> (nb. integer)
% (modulo) <value1> <value2> <value1 mod value2>
! (not) <value> <0 if value non-zero, 1 otherwise>
` (greater) <value1> <value2> <1 if value1 > value2, 0 otherwise>
> (right) PC -> right
< (left) PC -> left
^ (up) PC -> up
v (down) PC -> down
? (random) PC -> right? left? up? down? ???
_ (horizontal if) <boolean value> PC->left if <value>, else PC->right
| (vertical if) <boolean value> PC->up if <value>, else PC->down
" (stringmode) Toggles 'stringmode'
: (dup) <value> <value> <value>
\ (swap) <value1> <value2> <value2> <value1>
$ (pop) <value> pops <value> but does nothing
. (pop) <value> outputs <value> as integer
, (pop) <value> outputs <value> as ASCII
# (bridge) 'jumps' PC one farther; skips
over next command
g (get) <x> <y> <value at (x,y)>
p (put) <value> <x> <y> puts <value> at (x,y)
& (input value) <value user entered>
~ (input character) <character user entered>
@ (end) ends program