README.md

expressions

Parser for the expression language used in the spreadsheet plugin. This document outlines the Rust portion of the library. For JavaScript see the JS bindings.

Quickstart

In order to evaluate expressions, three things must happen;

1. A context object containing a [Data Provider](#Data Provider) must be registered
2. The list of all functions, variables and operators needs to be defined
3. The expression needs to be passed into the parser.

Data Provider

A data provider is an object which converts addresses into values. Addresses are arbitrary text tokens wrapped in braces. The provider determines their meaning. See the repl.rs for a feature-complete REPL.

#[derive(Copy, Clone)]
struct Provider;

impl expression::DataSource for Provider {
    fn query(&self, query: impl AsRef<str>) -> Option<expression::Object> {
        // Parse the query however you need to.
        // For example, the format `column:row`

        Some(Object::string("Hey!"))
    }
}

Context

Next you'll need a context object which holds state and variables and acts as an API to the expression engine. You can define your own functions, globals and operators here.

fn main() {
    let mut cx = expression::Context::new(Provider)
        .with_global("twelve", expression::Object::Number(12))
        .with_fn("print", |_cx, args| {
            println!("{:?}", args);
            Ok(expression::Object::Nothing)
        });

    assert_eq!(cx.evaluate("twelve"), expression::Object::Number(12));
}