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//! This module implements the backing representation of runtime
//! values in the Nix language.
use std::rc::Rc;
use std::{fmt::Display, path::PathBuf};
mod attrs;
mod builtin;
mod function;
mod list;
mod string;
mod thunk;
use crate::errors::ErrorKind;
use crate::opcode::StackIdx;
pub use attrs::NixAttrs;
pub use builtin::Builtin;
pub use function::{Closure, Lambda};
pub use list::NixList;
pub use string::NixString;
pub use thunk::Thunk;
#[warn(variant_size_differences)]
#[derive(Clone, Debug)]
pub enum Value {
Null,
Bool(bool),
Integer(i64),
Float(f64),
String(NixString),
Path(PathBuf),
Attrs(Rc<NixAttrs>),
List(NixList),
Closure(Closure),
Builtin(Builtin),
// Internal values that, while they technically exist at runtime,
// are never returned to or created directly by users.
Thunk(Thunk),
AttrPath(Vec<NixString>),
AttrNotFound,
DynamicUpvalueMissing(NixString),
Blueprint(Rc<Lambda>),
DeferredUpvalue(StackIdx),
}
// Helper macros to generate the to_*/as_* macros while accounting for
// thunks.
/// Generate an `as_*` method returning a reference to the expected
/// type, or a type error. This only works for types that implement
/// `Copy`, as returning a reference to an inner thunk value is not
/// possible.
/// Generate an `as_*/to_*` accessor method that returns either the
/// expected type, or a type error.
macro_rules! gen_cast {
( $name:ident, $type:ty, $expected:expr, $variant:pat, $result:expr ) => {
pub fn $name(&self) -> Result<$type, ErrorKind> {
match self {
$variant => Ok($result),
Value::Thunk(thunk) => Self::$name(&thunk.value()),
other => Err(type_error($expected, &other)),
}
}
};
}
/// Generate an `is_*` type-checking method.
macro_rules! gen_is {
( $name:ident, $variant:pat ) => {
pub fn $name(&self) -> bool {
match self {
$variant => true,
Value::Thunk(thunk) => Self::$name(&thunk.value()),
_ => false,
}
}
};
}
impl Value {
pub fn type_of(&self) -> &'static str {
match self {
Value::Null => "null",
Value::Bool(_) => "bool",
Value::Integer(_) => "int",
Value::Float(_) => "float",
Value::String(_) => "string",
Value::Path(_) => "path",
Value::Attrs(_) => "set",
Value::List(_) => "list",
Value::Closure(_) | Value::Builtin(_) => "lambda",
// Internal types
Value::Thunk(_)
| Value::AttrPath(_)
| Value::AttrNotFound
| Value::DynamicUpvalueMissing(_)
| Value::Blueprint(_)
| Value::DeferredUpvalue(_) => "internal",
}
}
gen_cast!(as_bool, bool, "bool", Value::Bool(b), *b);
gen_cast!(to_str, NixString, "string", Value::String(s), s.clone());
gen_cast!(to_attrs, Rc<NixAttrs>, "set", Value::Attrs(a), a.clone());
gen_cast!(to_list, NixList, "list", Value::List(l), l.clone());
gen_cast!(to_closure, Closure, "lambda", Value::Closure(c), c.clone());
gen_is!(is_number, Value::Integer(_) | Value::Float(_));
gen_is!(is_bool, Value::Bool(_));
}
impl Display for Value {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Value::Null => f.write_str("null"),
Value::Bool(true) => f.write_str("true"),
Value::Bool(false) => f.write_str("false"),
Value::Integer(num) => write!(f, "{}", num),
Value::String(s) => s.fmt(f),
Value::Path(p) => p.display().fmt(f),
Value::Attrs(attrs) => attrs.fmt(f),
Value::List(list) => list.fmt(f),
Value::Closure(_) => f.write_str("lambda"), // TODO: print position
Value::Builtin(builtin) => builtin.fmt(f),
// Nix prints floats with a maximum precision of 5 digits
// only.
Value::Float(num) => {
write!(f, "{}", format!("{:.5}", num).trim_end_matches(['.', '0']))
}
// Delegate thunk display to the type, as it must handle
// the case of already evaluated thunks.
Value::Thunk(t) => t.fmt(f),
// internal types
Value::AttrPath(path) => write!(f, "internal[attrpath({})]", path.len()),
Value::AttrNotFound => f.write_str("internal[not found]"),
Value::Blueprint(_) => f.write_str("internal[blueprint]"),
Value::DeferredUpvalue(_) => f.write_str("internal[deferred_upvalue]"),
Value::DynamicUpvalueMissing(name) => {
write!(f, "internal[no_dyn_upvalue({name})]")
}
}
}
}
impl PartialEq for Value {
fn eq(&self, other: &Self) -> bool {
match (self, other) {
// Trivial comparisons
(Value::Null, Value::Null) => true,
(Value::Bool(b1), Value::Bool(b2)) => b1 == b2,
(Value::List(l1), Value::List(l2)) => l1 == l2,
(Value::String(s1), Value::String(s2)) => s1 == s2,
// Numerical comparisons (they work between float & int)
(Value::Integer(i1), Value::Integer(i2)) => i1 == i2,
(Value::Integer(i), Value::Float(f)) => *i as f64 == *f,
(Value::Float(f1), Value::Float(f2)) => f1 == f2,
(Value::Float(f), Value::Integer(i)) => *i as f64 == *f,
// Optimised attribute set comparison
(Value::Attrs(a1), Value::Attrs(a2)) => Rc::ptr_eq(a1, a2) || { a1 == a2 },
// If either value is a thunk, the inner value must be
// compared instead. The compiler should ensure that
// thunks under comparison have been forced, otherwise it
// is a bug.
(Value::Thunk(lhs), rhs) => &*lhs.value() == rhs,
(lhs, Value::Thunk(rhs)) => lhs == &*rhs.value(),
// Everything else is either incomparable (e.g. internal
// types) or false.
// TODO(tazjin): mirror Lambda equality behaviour
_ => false,
}
}
}
fn type_error(expected: &'static str, actual: &Value) -> ErrorKind {
ErrorKind::TypeError {
expected,
actual: actual.type_of(),
}
}
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