standardform 0.2.1

Effortlessly operate on numbers like 2e19 or 2*10^4 and more with this Rust implementation of standard form. Simplify, convert, and manipulate large numerical expressions with ease.
Documentation 
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use decorum::Finite;
use nom::{
    branch::alt,
    bytes::complete::tag,
    combinator::{map, opt},
    error::ParseError,
    number::complete::double,
    sequence::{pair, preceded},
    IResult,
};

use crate::StandardForm;

/// Parses a string in standard form (scientific notation) and returns a `StandardForm` struct.
///
/// The standard form number can be written as , "mantissaeexponent",
/// "mantissaEexponent", or "mantissa*10^exponent". It supports both positive and negative exponents.
///
/// # Arguments
///
/// * `input` - The input string to parse.
///
/// # Returns
///
/// Returns a `Result` containing the parsed `StandardForm` struct if successful, or a parsing error.
pub fn parse_standard_form_with_required_exponent<'a, E>(
    input: &'a str,
) -> IResult<&str, StandardForm, E>
where
    E: ParseError<&'a str>,
{
    map(pair(double, parse_exponent), |(mantissa, exponent)| {
        StandardForm::new(Finite::from_inner(mantissa), exponent)
    })(input)
}

/// Parses a string in standard form (scientific notation) and returns a `StandardForm` struct.
///
/// The standard form number can be written as "mantissaEexponent", or "mantissa*10^exponent". It supports both positive and negative exponents.
///
/// # Arguments
///
/// * `input` - The input string to parse.
///
/// # Returns
///
/// Returns a `Result` containing the parsed `StandardForm` struct if successful, or a parsing error.
pub fn parse_standard_form_with_optional_exponent<'a, E>(
    input: &'a str,
) -> IResult<&str, StandardForm, E>
where
    E: ParseError<&'a str>,
{
    map(
        pair(double, opt(parse_exponent::<E>)),
        |(mantissa, exponent)| {
            StandardForm::new(Finite::from_inner(mantissa), exponent.unwrap_or(0))
        },
    )(input)
}

fn parse_exponent<'a, E>(input: &'a str) -> IResult<&str, i8, E>
where
    E: ParseError<&'a str>,
{
    preceded(
        alt((tag("e"), tag("E"), tag("*10^"))),
        map(double, |exp: f64| exp as i8),
    )(input)
}

#[cfg(test)]
mod parse_standardform_tests {
    use super::*;

    #[test]
    fn test_parse_standard_form_positive_exponent() {
        let input = "1.23e3"; // Example input: 1230.0
        match parse_standard_form_with_optional_exponent::<nom::error::Error<_>>(input) {
            Ok((_, standard_form)) => {
                assert_eq!(standard_form.mantissa(), &1.23);
                assert_eq!(standard_form.exponent(), &3);
            }
            Err(e) => panic!("Parsing error: {:?}", e),
        }
    }

    #[test]
    fn test_parse_standard_form_negative_exponent() {
        let input = "2.5*10^-2"; // Example input: 0.025
        match parse_standard_form_with_optional_exponent::<nom::error::Error<_>>(input) {
            Ok((_, standard_form)) => {
                assert_eq!(standard_form.mantissa(), &2.5);
                assert_eq!(standard_form.exponent(), &-2);
            }
            Err(e) => panic!("Parsing error: {:?}", e),
        }
    }

    #[test]
    fn test_parse_standard_form_no_exponent() {
        let input = "42"; // No exponent, should be treated as 42.0 * 10^0
        match parse_standard_form_with_optional_exponent::<nom::error::Error<_>>(input) {
            Ok((_, standard_form)) => {
                assert_eq!(standard_form.mantissa(), &4.2);
                assert_eq!(standard_form.exponent(), &1);
            }
            Err(e) => panic!("Parsing error: {:?}", e),
        }
    }

    #[test]
    fn test_parse_standard_form_star_exponent() {
        let input = "5*10^4"; // Example input: 50000.0
        match parse_standard_form_with_optional_exponent::<nom::error::Error<_>>(input) {
            Ok((_, standard_form)) => {
                assert_eq!(standard_form.mantissa(), &5.0);
                assert_eq!(standard_form.exponent(), &4);
            }
            Err(e) => panic!("Parsing error: {:?}", e),
        }
    }

    #[test]
    fn test_parse_standard_form_invalid_input() {
        let input = "invalid"; // Invalid input, should result in an error
        match parse_standard_form_with_optional_exponent::<nom::error::Error<_>>(input) {
            Ok(_) => panic!("Expected parsing error but got a result."),
            Err(_) => {} // Expected result
        }
    }
}