Rust code shared from the playground

playground.rs

type Oper = fn(isize, isize) -> isize;

pub struct WordProblem(&'static str);

impl WordProblem {
    pub fn new(command: &'static str) -> Self {
        WordProblem(command)
    }

    pub fn answer(&self) -> Result<isize, ()> {
        let tokens: Vec<_> = self.0
            .split(|c: char| !c.is_alphanumeric())
            .collect();

        let operator_plus = |a: isize, b: isize| -> isize { return a + b } as Oper;
        let operator_minus = |a: isize, b: isize| -> isize { return a - b } as Oper;
        let operator_multiply = |a: isize, b: isize| -> isize { return a * b } as Oper;
        let operator_divide = |a: isize, b: isize| -> isize { return a / b } as Oper;

        let mut accum = 0;
        let mut operator_func: &Oper = &operator_plus;
        for token in tokens {
            if let Ok(num) = token.parse::<isize>() {
                accum = operator_func(accum, num);
            } else {
                match token {
                    "plus" => operator_func = &operator_plus,
                    "minus" => operator_func = &operator_minus,
                    "multiplied" => operator_func = &operator_multiply,
                    "divided" => operator_func = &operator_divide,
                    _ => return Err(()),
                }
            }
        }

        Ok(accum)
    }
}