1 unstable release
0.1.7  Feb 21, 2024 

0.1.6 

0.1.5 

#2287 in Parser implementations
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YARER  The math expression Resolver
Yarer (Yet Another Rust Expression Resolver) is a library for resolving mathematical expressions. Internally it uses the shunting yard algorithm.
Example of usage of the library:
let session = Session::init();
let mut resolver = session.process("1+2"); // or even "(cos(10+e)+3*sin(9/pi))^2"
println!("The result is {}", resolver.resolve());
All that's needed is to get a new instance of the 'resolver' from a Session and hand over the expression to be analysed. The library just returns a variant natural number, or a decimal number if one exists in the expression (i.e '2.1+1') or is present a trigonometric function (i.e. 1/cos(x+1)).
Yarer handles variables and functions. Here an example:
let session = Session::init();
let mut resolver = session.process("1/cos(x^2)");
session.set("x",1);
println!("The result is {}", resolver.resolve());
and of course, the expression can be reevaluated if the variable changes.
//...
session.set("x",1);
println!("The result is {}", resolver.resolve());
session.set("x",0.001);
println!("The result is {}", resolver.resolve());
//...
The result can be simply casted into a i32 or a f64 (if decimal) simply with
let result: Number = resolver.resolve().unwrap();
let int : i32 = result.into();
// or
let float : f64 = result.into();
Yarer can be used also from command line, and behaves in a very similar manner to GNU bc
$ yarer
Yarer v.0.1.1  Yet Another Rust Expression Resolver.
License MIT OR Apache2.0
> (1+9)*(8+2)+0!
101
> (1./2)+atan(10)
1.1483608274590869
> x=10
> 3/sin(5*x^2)
6.41338354698791
> ln(1)
0
> log(10)
1
> 2^2
0.25
> 1/(log(10)+cos(0))^2
4
> 4.5+7.9*2.2
21.88
> 9801/(2206*sqrt(2)) // approx of PI
3.1415927300133055
News and Updates
Starting with Yarer version 0.1.7, natural numbers are implemented internally using BigInt from the num crate. Now it is possible to do calculations with arbitrarily large natural numbers.
$ yarer
Yarer v.0.1.1  Yet Another Rust Expression Resolver.
License MIT OR Apache2.0
> 78!
1132428117820629783145752115873204622873174957948825.....
> 2^78
302231454903657293676544
From Yarer version 0.1.5 it's possible to share a single session, and therefore a single heap of variables, for multiple resolvers. The library is not intended to be threadsafe.
let session = Session::init();
let mut res = session.process("x ^ 2");
let mut res2 = session.process("x!  (x1)!");
session.set("x", 10);
if let (Ok(a), Ok(b)) = (res.resolve(),res2.resolve()) {
println!("{} {}", a, b); // 100 3265920
}
Builtin Defined Functions
There are several math functions defined that you can use in your expression. More to come! There are many examples of processed expressions in the integration test file.
Sin
Cos
Tan
ASin
ACos
ATan
Ln
Log
Abs
Sqrt
Builtin Defined Constants
There are 2 predefined math constants at the moment:
PI > 3.14159265...
e > 2.7182818...
Execute
To run it from cargo, just type:
cargo run q 
For logging debug just run with:
env RUST_LOG=yarer=debug cargo run q 
or to build and install a release from the code:
cargo build release
cargo install path .
./target/release/yarer
Internal Implementation
Each expression is the result of an evaluation by the following actors
Step1  Parser: A string is "regexed" and converted into a token array.
Step 2  RpnResolver: Using the Shunting Yard algorithm the token array is converted from infix to postfix notation.
Step 3  RpnResolver: The resulting RPN (Reverse Polish Notation) expression is evaluated.
Worth to mention that the Session is responsible to store all variables (and constants) that are borrowed by all the RpnResolvers.
Contribution
Besides being stable, Yarer is a work in progress. If you have suggestions for features (i.e. more math functions to implement), or if you find any issues in the code, design, interface, etc, please feel free to share them on our GitHub.
I appreciate very much your feedback!
Dependencies
~10MB
~186K SLoC