README.md

shunting

A library for evaluating math expressions via the shunting-yard algorithm. Handles operators, functions, variables, and random variables.

Quick Start

use shunting::{ShuntingParser, MathContext};

let input = "sin(0.2)^2 + cos(0.2)^2";
let expr = ShuntingParser::parse_str(input).unwrap();
let result = MathContext::new().eval(&expr).unwrap();
println!("{} = {}", expr, result);

MathContext

MathContext keeps state across multiple evaluations. Built-in variables: pi, e.

let ctx = MathContext::new();

// Set a variable
let expr = ShuntingParser::parse_str("a = sin(0.2)^2 + cos(0.2)^2").unwrap();
ctx.eval(&expr).unwrap();
let result = ctx.eval(&ShuntingParser::parse_str("a").unwrap()).unwrap();
assert_eq!(result, 1.0);

Random Variables

Use compile to build expressions with random variables:

let expr = ShuntingParser::parse_str("normal(0, 1) + 5").unwrap();
let rv = MathContext::new().compile(&expr).unwrap();
println!("{}", rv.eval());

Histogram

Sample a random variable and build a histogram:

let expr = ShuntingParser::parse_str("normal(0, 1)").unwrap();
let rv = MathContext::new().compile(&expr).unwrap();
let hist = rv.histogram::<10>(1000);
println!("{:?}", hist);

MathOp

The MathOp enum represents a value in the expression system:

• MathOp::Number(f64) — a constant value
• MathOp::RandVar — a random variable (e.g. normal(0, 1))
• MathOp::Dynamic — a lazily-evaluated expression (e.g. a + b where a or b is a variable)

Supported Functions

Function	Description
sin, cos	Trigonometric
abs	Absolute value
log	Base-10 log
ln	Natural log
atan2	Arc tangent of two arguments
max, min	Min/max of all arguments
nCr	Combinations
nPr	Permutations
nMCr	Multicombinations
nMPr	n^r (ordered with replacement)
rand	Random value in [0, arg)
normal(μ, σ)	Normal distribution
uniform(a, b)	Uniform distribution
lognormal(μ, σ)	Log-normal distribution

Operators

Binary: +, -, *, /, %, ^ (or **)
Unary: - (negation), ! (factorial via gamma)

The shunting REPL

The math REPL is available via the toxtools workspace crate:

$ cargo run -p toxtools --bin shunting
>> 4!
24
>> a = sin(0.2)^2 + cos(0.2)^2
>> a
1
>> (-3)!
NaN
>> (84 % (5/2)) !
1.32934
>> pi * 2.1^2 / cbrt(-(6+3))
-6.660512