Function reduce

crates/vm/src/stdlib/_functools.rs:28–58

(args: ReduceArgs, vm: &VirtualMachine)

    #[pyfunction]
    fn reduce(args: ReduceArgs, vm: &VirtualMachine) -> PyResult {
        let ReduceArgs {
            function,
            iterator,
            initial,
        } = args;
        let mut iter = iterator.iter_without_hint(vm)?;
        // OptionalOption distinguishes between:
        // - Missing: no argument provided → use first element from iterator
        // - Present(None): explicitly passed None → use None as initial value
        // - Present(Some(v)): passed a value → use that value
        let start_value = if let Some(val) = initial.into_option() {
            // initial was provided (could be None or Some value)
            val.unwrap_or_else(|| vm.ctx.none())
        } else {
            // initial was not provided at all
            iter.next().transpose()?.ok_or_else(|| {
                let exc_type = vm.ctx.exceptions.type_error.to_owned();
                vm.new_exception_msg(
                    exc_type,
                    "reduce() of empty sequence with no initial value".into(),
                )
            })?
        };

        let mut accumulator = start_value;
        for next_obj in iter {
            accumulator = function.call((accumulator, next_obj?), vm)?
        }
        Ok(accumulator)
    }

    // Placeholder singleton for partial arguments
    // The singleton is stored as _instance on the type class