add_asterisks public domain

gistfile1.txt

I hereby release the following code with the CC0/public domain license:



/*
EXTREMELY Janky function that tries to put asterisks in the proper places to be parsed. This is so cursed. But it works, and I hopefully won't ever have to touch it again.
One limitation though, variables with multiple characters like `pi` cannot be multiplied (like `pipipipi` won't result in `pi*pi*pi*pi`). But that's such a niche use case (and that same thing could be done by using exponents) that it doesn't really matter.
In the future I may want to completely rewrite this or implement this natively into mevel-rs (which would probably be good to do)
*/
pub fn add_asterisks(function_in: String) -> String {
    let function = function_in.replace("log10(", "log(").replace("pi", "π"); // pi -> π and log10 -> log
    let valid_variables: Vec<char> = "xeπ".chars().collect();
    let letters: Vec<char> = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
        .chars()
        .collect();
    let numbers: Vec<char> = "0123456789".chars().collect();
    let function_chars: Vec<char> = function.chars().collect();
    let mut output_string: String = String::new();
    let mut prev_chars: Vec<char> = Vec::new();
    for c in function_chars {
        let mut add_asterisk: bool = false;
        let prev_chars_len = prev_chars.len();

        let prev_prev_char = if prev_chars_len >= 2 {
            *prev_chars.get(prev_chars_len - 2).unwrap()
        } else {
            ' '
        };

        let prev_char = if prev_chars_len >= 1 {
            *prev_chars.get(prev_chars_len - 1).unwrap()
        } else {
            ' '
        };

        let c_letters_var = letters.contains(&c) | valid_variables.contains(&c);
        let prev_letters_var = valid_variables.contains(&prev_char) | letters.contains(&prev_char);

        if prev_char == ')' {
            if (c == '(') | numbers.contains(&c) | c_letters_var {
                add_asterisk = true;
            }
        } else if c == '(' {
            if (valid_variables.contains(&prev_char)
                | (')' == prev_char)
                | numbers.contains(&prev_char))
                && !letters.contains(&prev_prev_char)
            {
                add_asterisk = true;
            }
        } else if numbers.contains(&prev_char) {
            if (c == '(') | c_letters_var {
                add_asterisk = true;
            }
        } else if letters.contains(&c) {
            if numbers.contains(&prev_char)
                | (valid_variables.contains(&prev_char) && valid_variables.contains(&c))
            {
                add_asterisk = true;
            }
        } else if (numbers.contains(&c) | c_letters_var) && prev_letters_var {
            add_asterisk = true;
        }

        if add_asterisk {
            output_string += "*";
        }

        prev_chars.push(c);
        output_string += &c.to_string();
    }

    output_string.replace('π', "pi") // π -> pi
}