use cpc::{eval, Unit::*}

match eval("3m + 1cm", true, Celcius) {
    Ok(answer) => {
        // answer: Number { value: 301, unit: Unit::cm }
        println!("Evaluated value: {} {:?}", answer.value, answer.unit)
    },
    Err(e) => {
        println!(e)
    }
}

Examples

3 + 4 * 2

8 % 3

(4 + 1)km to light years

10m/2s * 5s

1 lightyear * 0.001mm in km2

1m/s + 1mi/h in kilometers per h

round(sqrt(2)^4)! liters

10% of abs(sin(pi)) horsepower to watts

Supported unit types

Normal numbers
Time
Length
Area
Volume
Mass
Digital storage (bytes etc)
Energy
Power
Pressure
Speed
Temperature

Accuracy

cpc Uses 128-bit Decimal Floating Point (d128) numbers instead of Binary Coded Decimals for better accuracy. The result cpc gives will still not always be 100% accurate. I would recommend rounding the result to 20 decimals or less.

Performance

In my case, I can expect eval() to take 100-200ms, and this scales pretty alright. However, putting numbers with a lot of digits into functions result in pretty poor performance. log(e) is one of the worst, and takes 500ms for me.

Errors

cpc returns Results with basic strings as errors. Just to be safe, you may want to handle panics (You can do that using std::panic::catch_unwind).

Dev Instructions

Get started

Install Rust. This project was built in Rust 1.40.

Commands

Run cpc with a CLI argument as input:

cargo run -- '100ms to s'

Run with debugging, which shows some extra logs:

cargo run -- '100ms to s' --debug

Run tests:

cargo test

Adding a unit

1. Add the unit

In src/units.rs, units are specified like this:

pub enum UnitType {
  Time,
  // etc
}

// ...

create_units!(
  Nanosecond:         (Time, d128!(1)),
  Microsecond:        (Time, d128!(1000)),
  // etc
)

The number associated with a unit is it's "weight". For example, if a second's weight is 1, then a minute's weight is 1000.

I have found translatorscafe.com and calculateme.com to be good websites for unit convertion. Wikipedia is worth looking at as well.

2. Add a test for the unit

Make sure to also add a test for each unit. The tests look like this:

assert_eq!(convert_test(1000.0, Meter, Kilometer), 1.0);

Basically, 1000 Meter == 1 Kilometer.

3. Add the unit to the lexer

Text is turned into tokens (some of which are units) in lexer.rs. Here's one example:

// ...
match string {
  "h" | "hr" | "hrs" | "hour" | "hours" => tokens.push(Token::Unit(Hour)),
  // etc
}
// ...

Potential Improvements

General

Support for math in 6'4" syntax, like 3'+2'4". Currently needs to be written like 3'+3'+4"
The functions in units.rs have a lot of manual if statements. This could probably be replaced with a pretty advanced macro.
Support for lexing words, like one billion

Potential unit types

Nice list of units: https://support.google.com/websearch/answer/3284611

Currency: How would you go about dynamically updating the weights?
Fuel consumption
Data transfer rate
Color codes
Force
Roman numerals
Angles
Electric current, capacitance, charge, conductance, volts
Flow rate
Frequency