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|
//! This module implements the runtime representation of a Nix
//! builtin.
//!
//! Builtins are directly backed by Rust code operating on Nix values.
use crate::vm::generators::Generator;
use super::Value;
use std::{
fmt::{Debug, Display},
rc::Rc,
};
/// Trait for closure types of builtins.
///
/// Builtins are expected to yield a generator which can be run by the VM to
/// produce the final value.
///
/// Implementors should use the builtins-macros to create these functions
/// instead of handling the argument-passing logic manually.
pub trait BuiltinGen: Fn(Vec<Value>) -> Generator {}
impl<F: Fn(Vec<Value>) -> Generator> BuiltinGen for F {}
#[derive(Clone)]
pub struct BuiltinRepr {
name: &'static str,
/// Optional documentation for the builtin.
documentation: Option<&'static str>,
arg_count: usize,
func: Rc<dyn BuiltinGen>,
/// Partially applied function arguments.
partials: Vec<Value>,
}
pub enum BuiltinResult {
/// Builtin was not ready to be called (arguments missing) and remains
/// partially applied.
Partial(Builtin),
/// Builtin was called and constructed a generator that the VM must run.
Called(&'static str, Generator),
}
/// Represents a single built-in function which directly executes Rust
/// code that operates on a Nix value.
///
/// Builtins are the only functions in Nix that have varying arities
/// (for example, `hasAttr` has an arity of 2, but `isAttrs` an arity
/// of 1). To facilitate this generically, builtins expect to be
/// called with a vector of Nix values corresponding to their
/// arguments in order.
///
/// Partially applied builtins act similar to closures in that they
/// "capture" the partially applied arguments, and are treated
/// specially when printing their representation etc.
#[derive(Clone)]
pub struct Builtin(Box<BuiltinRepr>);
impl From<BuiltinRepr> for Builtin {
fn from(value: BuiltinRepr) -> Self {
Builtin(Box::new(value))
}
}
impl Builtin {
pub fn new<F: BuiltinGen + 'static>(
name: &'static str,
documentation: Option<&'static str>,
arg_count: usize,
func: F,
) -> Self {
BuiltinRepr {
name,
documentation,
arg_count,
func: Rc::new(func),
partials: vec![],
}
.into()
}
pub fn name(&self) -> &'static str {
self.0.name
}
pub fn documentation(&self) -> Option<&'static str> {
self.0.documentation
}
/// Apply an additional argument to the builtin. After this, [`call`] *must*
/// be called, otherwise it may leave the builtin in an incorrect state.
pub fn apply_arg(&mut self, arg: Value) {
self.0.partials.push(arg);
debug_assert!(
self.0.partials.len() <= self.0.arg_count,
"Tvix bug: pushed too many arguments to builtin"
);
}
/// Attempt to call a builtin, which will produce a generator if it is fully
/// applied or return the builtin if it is partially applied.
pub fn call(self) -> BuiltinResult {
if self.0.partials.len() == self.0.arg_count {
BuiltinResult::Called(self.0.name, (self.0.func)(self.0.partials))
} else {
BuiltinResult::Partial(self)
}
}
}
impl Debug for Builtin {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "builtin[{}]", self.0.name)
}
}
impl Display for Builtin {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
if !self.0.partials.is_empty() {
f.write_str("<<primop-app>>")
} else {
f.write_str("<<primop>>")
}
}
}
/// Builtins are uniquely identified by their name
impl PartialEq for Builtin {
fn eq(&self, other: &Self) -> bool {
self.0.name == other.0.name
}
}
|
