L-System based FizzBuzz implementations (using https://thi.ng/lsys)

lsys-fizzbuzz.ts

import type { Fn2 } from "@thi.ng/api";
import {
    DEFAULT,
    expand,
    interpret,
    type LSysSymbol,
    type RuleImplementations,
} from "@thi.ng/lsys";

// iterative rule expansion
const fizzbuzz = expand(
    {
        start: ["_1"],
        _1: ["1", "_2"],
        _2: ["2", "_3"],
        _3: ["fizz", "_4"],
        _4: ["4", "_5"],
        _5: ["buzz", "_6"],
        _6: ["fizz", "_7"],
        _7: ["7", "_8"],
        _8: ["8", "_9"],
        _9: ["fizz", "_10"],
        _10: ["buzz", "_11"],
        _11: ["11", "_12"],
        _12: ["fizz", "_13"],
        _13: ["13", "_14"],
        _14: ["14", "_15"],
        _15: ["fizz buzz", "end"],
    },
    "start",
    100
);

console.log([...fizzbuzz].join(" "));
// 1 2 fizz 4 buzz fizz 7 8 fizz 10 11 fizz 13 14 fizz buzz end

// alternative approach:
// attaching a L-System iterpreter implementing a simple stack machine VM
// for Forth-like execution (incl. quotations)

// VM state is a 2-tuple of `[current stack, scopes]`
type VmCtx = [any[], any[]];

// VM operators (i.e. mapping L-System symbols to actions)
const VM: RuleImplementations<VmCtx> = {
    // any unmatches symbol will be pushed on stack
    [DEFAULT]: ([stack]: any[], x: any) => stack.push(x),

    // quoation handling
    "[": (ctx) => (ctx[1].push(ctx[0]), (ctx[0] = [])),
    "]": (ctx) => {
        const parent = ctx[1].pop();
        parent.push(ctx[0]);
        ctx[0] = parent;
    },
};

// all other VM ops are deferrable (i.e. will only execute in the root scope,
// otherwise the symbol is quoted and just pushed on current stack...)
const DEFERED_OPS: RuleImplementations<VmCtx> = {
    // print TOS: ( x -- )
    ".": (ctx) => console.log(ctx[0].pop()!),

    // 2-branch conditional: ( test truthy falsy -- )
    ifelse: (ctx) => {
        const [falsy, truthy] = [ctx[0].pop(), ctx[0].pop()];
        interpret(ctx, VM, ctx[0].pop() ? truthy : falsy);
    },

    // duplicate TOS: ( x -- x x )
    dup: ([stack]) => stack.push(stack[stack.length - 1]),

    // remove TOS: ( x -- )
    drop: ([stack]) => stack.pop(),

    // swap two topmost values: ( x y -- y x )
    swap: ([stack]) => stack.splice(stack.length - 2, 0, stack.pop()),

    // compute modulo: ( x y -- x%y )
    mod: ([stack]) => {
        const x = stack.pop()!;
        stack.push(stack.pop()! % x);
    },

    // concatenate strings: ( x y -- x+y )
    concat: ([stack]) => {
        const [b, a] = [stack.pop(), stack.pop()];
        stack.push(a + b);
    },
};

// helper function to allow op be quotable
const defer =
    (id: string, fn: Fn2<VmCtx, LSysSymbol, void>) =>
    (ctx: VmCtx, sym: LSysSymbol) =>
        !ctx[1].length ? fn(ctx, sym) : ctx[0].push(id);

// inject all deferred ops
for (let [id, op] of Object.entries(DEFERED_OPS)) {
    VM[id] = defer(id, op);
}

// L-System ruleset (aka source code) for VM
const fizzbuzzVM = [
    ...expand(
        {
            start: ["_1"],
            empty: ["[", "", "]"],
            _fizz: ["[", "fizz", "]"],
            _buzz: ["[", "buzz", "]"],
            label: ["[", ".", "drop", "]"],
            counter: ["[", "drop", ".", "]"],
            "fizz?": [3, "mod", "empty", "_fizz", "ifelse"],
            "buzz?": [5, "mod", "empty", "_buzz", "ifelse"],
            fizzbuzz: [
                "dup",
                "dup",
                "fizz?",
                "swap",
                "buzz?",
                "concat",
                "dup",
                "label",
                "counter",
                "ifelse",
            ],
            _1: [1, "fizzbuzz", "_2"],
            _2: [2, "fizzbuzz", "_3"],
            _3: [3, "fizzbuzz", "_4"],
            _4: [4, "fizzbuzz", "_5"],
            _5: [5, "fizzbuzz", "_6"],
            _6: [6, "fizzbuzz", "_7"],
            _7: [7, "fizzbuzz", "_8"],
            _8: [8, "fizzbuzz", "_9"],
            _9: [9, "fizzbuzz", "_10"],
            _10: [10, "fizzbuzz", "_11"],
            _11: [11, "fizzbuzz", "_12"],
            _12: [12, "fizzbuzz", "_13"],
            _13: [13, "fizzbuzz", "_14"],
            _14: [14, "fizzbuzz", "_15"],
            _15: [15, "fizzbuzz", "end"],
        },
        "start",
        100
    ),
];

// output expanded rules
console.log(fizzbuzzVM.join(" "));
// 1 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 2 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 3 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 4 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 5 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 6 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 7 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 8 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 9 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 10 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 11 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 12 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 13 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 14 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse 15 dup dup 3 mod [  ] [ fizz ] ifelse swap 5 mod [  ] [ buzz ] ifelse concat dup [ . drop ] [ drop . ] ifelse end

// execute
interpret([[], []], VM, fizzbuzzVM);

// Output:
// 1
// 2
// fizz
// 4
// buzz
// fizz
// 7
// 8
// fizz
// buzz
// 11
// fizz
// 13
// 14
// fizzbuzz