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#8 in #correct
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calc_lib
A crate for evaluating algebraic expressions from input using correct order of operations.
This was designed originally for use in terminal based calculator apps.
Features
- Basic algebraic operations
- Proper order of operations (functions are always evaluated first, then PEMDAS)
- Optional defined variables
- Integer operations and floating point operations (either/or)
- Functions such as log, sin, cos, tan, etc.
- Optional defined functions
Planned Features
- equation validation (such as
2 + 2 = 4
which is valid, and2 + 2 = 5
which is not) - solving for a variable (such as
x + 2 = 4
will result inx = 2
)
Features that may be implemented in the future
- solving for multiple variables (such as
3x - y = 7
,2x + y = 8
will result inx = 3
,y = 2
)
Default functions
accessed with Functions::default();
log(base, value)
sqrt(value)
sin(value)
cos(value)
tan(value)
Custom Error system:
- Exposes the Error enum which allows the user to determine what type of error occurred, and have all the relevant information about it
- Allows for the user to handle errors in their own way if needed, but they can also just be printed out.
Examples:
Integer equations:
// evaluates an algebraic equation
use calc_lib::evaluate;
fn main() {
// the equation to evaluate
let eval = evaluate("1 + 2 * 3");
// print out errors if they occur, or handle them another way
if eval.is_err() {
panic!("{}", eval.err().unwrap());
}
// the result is a f64, which can then be used as needed
// here, I am just asserting that it is the value it should be.
assert_eq!(eval.unwrap() as i32, 7);
}
Decimal Equations:
use calc_lib::evaluate;
fn main() {
// define the expression
let expression = "1.3 + 2.5 * 3.1";
// evaluate the expression
let eval = evaluate(expression);
// handle errors that may occur
if eval.is_err() {
panic!("{}", x.unwrap_err());
}
assert_eq!(eval.unwrap(), 9.05);
}
Solving with variables:
use calc_lib::{evaluate_with_defined, Definitions, Functions, Error};
fn main() {
// define x as 16
let mut defs = Definitions::new();
defs.register("x", 16);
// create the functions list
// this defines an empty Functions struct with no functions.
// for functions like log, sqrt, sin, cos, tan, etc., use `Functions::default()`
let mut funcs = Functions::new();
// this shows the definition of the log function,
// exactly how it is implemented in `Functions::default();`
funcs.register("log", |args| {
// args is of type Vec<f64>
// this takes 2 arguments: base, number
if args.len() != 2 {
return Err(Error::arg_count("log", 2, args.len()));
}
// return the value
Ok(args[1].log(args[0]))
});
// evaluate the expression and verify the results
let eval = evaluate_with_defined("log(2, x)", Some(&defs), Some(&funcs));
if eval.is_err() {
panic!("{}", eval.unwrap_err());
}
assert_eq!(eval.unwrap(), 4.0);
}