Crate partial_application

The partial! macro allows partial application of a function.

Invoking partial!(some_fn => arg0, _, arg2, _) will return the closure |x1, x3| some_fn(arg0, x1, arg2, x3).
Move closures can be created by adding move in front of the function: partial!(move ..).

Due to the straightforward translation, expression arguments will be reevaluated on every call. Pre-compute values if you don't want this.
partial!(some_fn => _, _, rand::thread_rng().gen::<u8>(), { println!("called again"); arg3 })
The closure created from the above will get a new random number and print "called again" on every call.

#[macro_use]
extern crate partial_application;

fn foo(a: i32, b: i32, c: i32, d: i32, mul: i32, off: i32) -> i32 {
    (a + b*b + c.pow(3) + d.pow(4)) * mul - off
}

fn main() {
    let bar = partial!(foo => _, _, 10, _, 10, 10);
    assert_eq!(
        foo(15, 15, 10, 42, 10, 10),
        bar(15, 15,     42)
    );
}

You can also use a comma (,) or semicolon (;) instead of the arrow =>. This strange syntax choice is due to limitations imposed on us by the macro system. No other tokens may follow the expression token for the function.

Macros

partial

The macro that creates a wrapping closure for a partially applied function