_mex_ a parser/evaluator for simple mathematical expressions, with _no_ dependencies at all. Currently, it supports only a _tiny_ amount of syntax. Here are some valid expressions:
```
>> 10
10
>> 10 - 3 * 10
-20
>> π = 3.1415926536
3.1415926536
>> 5 * π
15.707963268
```
And that's it, for now.
It supports the following operators: `+`, `-`, `*`, `/`, `=`.
But it's easy to add more (by editing the source).
The crate can be used as a binary or a library. The binary is a REPL, where you enter single expressions line by line and get the result given back to you. An example of the library is below:
```rust
use mex::parser;
use mex::evaluator;
use mex::evaluator::context;
use mex::evaluator::object;
fn main() {
let input = "2 * x";
let mut parse = parser::Parser::new(input);
let mut context = context::Context::new();
context.set(&String::from("x"), object::Object::Number(13.5));
match parse.parse() {
Ok(node) => {
match evaluator::eval_node_in(node, &mut context) {
Ok(result) => println!("{}", result),
Err(err) => println!("eval error: {:?}", err),
}
}
Err(e) => println!("parse error: {:?}", e),
};
}
```
In the future, I'd like to add these things:
- Simple API for simple uses
- e.g. `mex::evaluate("1 + 2")` → `3`
- Functions
- e.g. `f(x, y) = x + y`
- e.g. `f(2, 3)` → `5`
- Customisation / options
- Probably via bitflags
- Things like which operators are allowed, if you're allowed to define variables, etc...
- Builtins
- e.g. `π`, `e`, `sin(θ)`
- Going back to the last point: builtins should be optional
- Multiple expressions in one
- e.g. `5 + {1, 2, 3}` → `6`, `7`, and `8`
- They would be returned in a hash set, probably
- Symbolic Expressions
- e.g. `'x = a + b'` (maybe with different delimiters)
- Can be either equations (i.e. with equals), or just simple expressions
- `where` clause
- e.g. `'a + b' where a = 2, b = 10` → `12`
- `solve ... for`
- e.g. `solve 'a = x + b' for x` → `'x = a - b'`
- e.g. `(solve 'a = x + b' for x) where a = 5, b = 2` → `3`
- e.g. `solve 'x^2 + 3x + 2' for x` → `(x + 1)(x + 2)`
- Maybe even integration/differentiation