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use super::operator::Operator;
use std::collections::HashMap;
pub struct PostfixCalculator<'a> {
operators: HashMap<&'a str, Operator<'a>>,
}
impl<'a> PostfixCalculator<'a> {
pub fn new() -> Self {
let mut operators = HashMap::new();
operators.insert("+", Operator::binary(&|a, b| Ok(a + b)));
operators.insert("-", Operator::binary(&|a, b| Ok(a - b)));
operators.insert("*", Operator::binary(&|a, b| Ok(a * b)));
operators.insert("/", Operator::binary(&|a, b| Ok(a / b)));
Self { operators }
}
pub fn with_operators(
custom: &'a HashMap<&'a str, Operator<'a>>,
) -> Result<Self, &'static str> {
let mut operators = HashMap::new();
operators.insert("+", Operator::binary(&|a, b| Ok(a + b)));
operators.insert("-", Operator::binary(&|a, b| Ok(a - b)));
operators.insert("*", Operator::binary(&|a, b| Ok(a * b)));
operators.insert("/", Operator::binary(&|a, b| Ok(a / b)));
for (name, operator) in custom.iter() {
if let Ok(_) = name.parse::<f64>() {
return Err("Invalid operator identifier");
}
operators.insert(*name, Operator::from(&operator));
}
Ok(Self { operators })
}
pub fn evaluate(&self, tokens: &[&str]) -> Result<f64, &'static str> {
let mut stack: Vec<f64> = vec![];
for token in tokens {
if let Ok(operand) = token.parse::<f64>() {
stack.push(operand);
} else {
if stack.len() < 2 {
return Err("Too few operands");
}
let result = match self.operators.get(*token) {
Some(operator) => match *operator {
Operator::Binary(f) => {
if stack.len() < 2 {
return Err("Too few operands");
}
let op2 = stack.pop().unwrap();
let op1 = stack.pop().unwrap();
(*f)(op1, op2)
}
Operator::Unary(f) => {
if stack.len() < 1 {
return Err("Too few operands");
}
let op = stack.pop().unwrap();
(*f)(op)
}
},
_ => return Err("Unrecognized operator"),
};
match result {
Ok(result) => stack.push(result),
Err(e) => return Err(e),
}
}
}
if stack.len() != 1 {
Err("Too many operands!")
} else {
Ok(stack.pop().unwrap())
}
}
}