Struct Expr

pub struct Expr { /* private fields */ }

A parsed and optimized mathematical expression.

Examples

let expr = Expr::parse("3 + 5 * 2").unwrap();
assert_eq!(expr.eval(None), Ok(13.0));

let mut context :HashMap<String,f64> = HashMap::new();
context.insert("a".into(), 42.0);
let expr = Expr::parse("-2 * a").unwrap();
assert_eq!(expr.eval(&context), Ok(-84.0));

Implementations

impl Expr

pub fn parse(expression: &str) -> Result<Self, Error>

Parse the given mathematical expression into an Expr.

Examples

// A valid expression
assert!(Expr::parse("3 + 5 * 2").is_ok());
// an invalid expression
assert!(Expr::parse("3eff + 5 * 2").is_err());

pub fn eval<'a, C>(&self, context: C) -> Result<f64, Error>

where C: Into<Option<&'a HashMap<String, f64>>>,

Evaluate the expression in a given optional context.

Examples

let expr = Expr::parse("3 + 5 * 2").unwrap();
assert_eq!(expr.eval(None), Ok(13.0));

let expr = Expr::parse("3 + a").unwrap();

let mut context :HashMap<String,f64> = HashMap::new();
context.insert("a".into(), -5.0);
assert_eq!(expr.eval(&context), Ok(-2.0));
context.insert("a".into(), 2.0);
assert_eq!(expr.eval(&context), Ok(5.0));

Trait Implementations

impl Clone for Expr

fn clone(&self) -> Expr

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Expr

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for Expr

fn eq(&self, other: &Expr) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for Expr