flow_impl

The root crate defined a trait that implementations of flow 'functions' must implement in order for them to be invoked by the flowr (or other) runtime.

Derive Macro

Also, in the flow_impl_derive subdirectory a Dervice macro called FlowImpl is defined and implemented.

This should be used on the structure that implements the function, in order that when compiled for the wasm32 target code is inserted to allocate memory (alloc) and to serialize and deserialize the data passed across the native/wasm boundary.

Example implementation

An example implementation using both of these (the trait and the derive macro) is shown:

extern crate core;
extern crate flow_impl;
extern crate flow_impl_derive;
#[macro_use]
extern crate serde_json;

use flow_impl::implementation::{Implementation, RUN_AGAIN, RunAgain};
use flow_impl_derive::FlowImpl;
use serde_json::Value;

#[derive(FlowImpl)]
pub struct Compare;

/*
    A compare operator that takes two numbers (for now) and outputs the comparisons between them
*/
impl Implementation for Compare {
    fn run(&self, mut inputs: Vec<Vec<Value>>) -> (Option<Value>, RunAgain) {
        let left = inputs[0].remove(0).as_i64().unwrap();
        let right = inputs[1].remove(0).as_i64().unwrap();

        let output = json!({
                    "equal" : left == right,
                    "lt" : left < right,
                    "gt" : left > right,
                    "lte" : left <= right,
                    "gte" : left >= right,
                });

        (Some(output), RUN_AGAIN)
    }
}