paiza.ioでrust その12

概要

paiza.ioでrustやってみた。
練習問題やってみた。

練習問題

Forthインタープリターを書いて、数9を4個つかって1から15までの数を表す式を実行せよ。

サンプルコード

const MAXVAL: usize = 20;
fn push(val: &mut [f32; MAXVAL], sp: &mut i32, op: f32) {
	if *sp < MAXVAL as i32
	{
		val[*sp as usize] = op;
		*sp += 1;
	}
	else
	{
		println!("error: stack full, can't push {}", op);
	}
}
fn pop(val: &mut [f32; MAXVAL], sp: &mut i32) -> f32 {
	if *sp > 0
	{
		*sp -= 1;
		return val[*sp as usize];
	}
	else
	{
		println!("error: stack empty");
		return 0.0;
	}
}

fn Forth(s: &str) {
	let mut sp: i32 = 0;
	let mut val: [f32; MAXVAL] = [0.0; MAXVAL];
	//println!("{}", s);
    let strs = s.split_whitespace();
	//println!("{:?}", strs); 
	let cs: Vec<&str> = s.split_whitespace().collect::<Vec<_>>();
	//println!("{:?}", cs); 
	for token in cs
	{
		//println!("{}", token);
		match token
    	{
			"+" => {
				let right = pop(&mut val, &mut sp);
				let left = pop(&mut val, &mut sp);
                push(&mut val, &mut sp, left + right);
    		}
			"-" => {
				let right = pop(&mut val, &mut sp);
				let left = pop(&mut val, &mut sp);
                push(&mut val, &mut sp, left - right);
		    }
			"*" => {
				let right = pop(&mut val, &mut sp);
				let left = pop(&mut val, &mut sp);
                push(&mut val, &mut sp, left * right);
			}
			"/" => {
				let right = pop(&mut val, &mut sp);
				let left = pop(&mut val, &mut sp);
                push(&mut val, &mut sp, left / right);
			}
			"." => {
				let right = pop(&mut val, &mut sp);
        		println!("{}", right);
			}
			"dup" => {
				let right = pop(&mut val, &mut sp);
                push(&mut val, &mut sp, right);
                push(&mut val, &mut sp, right);
    		}
			"drop" => {
				let right = pop(&mut val, &mut sp);
    		}
			_ => {
			    let number: f32 = token.parse::<f32>().expect("REASON");
				push(&mut val, &mut sp, number);
			}
		}
	}
}

fn main() {
    Forth("9 9 - 9 9 / .");
    Forth("9 9 / 9 9 / + .");
    Forth("9 9 + 9 + 9 / .");
    Forth("9 9 9 + 9 / dup + .");
    Forth("9 9 9 + 9 / dup + - .");
    Forth("9 dup 9 + 9 + 9 / - .");
    Forth("9 9 9 + 9 / - .");
    Forth("9 9 9 drop 9 / - .");
    Forth("9 9 - 9 * 9 + .");
    Forth("9 9 / 9 dup 9 / + .");
    Forth("9 9 9 + 9 / + .");
    Forth("9 dup 9 9 + + 9 / + .");
    Forth("9 9 9 + 9 / dup + + .");
    Forth("9 dup 9 9 + 9 / dup + - + .");
    Forth("9 dup dup 9 + 9 + 9 / - + .");
}

実行結果

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成果物

以上