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-rw-r--r--dhall/src/semantics/nze/lazy.rs64
-rw-r--r--dhall/src/semantics/nze/mod.rs1
-rw-r--r--dhall/src/semantics/nze/value.rs53
3 files changed, 83 insertions, 35 deletions
diff --git a/dhall/src/semantics/nze/lazy.rs b/dhall/src/semantics/nze/lazy.rs
new file mode 100644
index 0000000..d361313
--- /dev/null
+++ b/dhall/src/semantics/nze/lazy.rs
@@ -0,0 +1,64 @@
+use once_cell::unsync::OnceCell;
+use std::cell::Cell;
+use std::fmt::Debug;
+use std::ops::Deref;
+
+pub trait Eval<Tgt> {
+ fn eval(self) -> Tgt;
+}
+
+/// A value which is initialized from a `Src` on the first access.
+pub struct Lazy<Src, Tgt> {
+ /// Exactly one of `src` of `tgt` must be set at a given time.
+ /// Once `src` is unset and `tgt` is set, we never go back.
+ src: Cell<Option<Src>>,
+ tgt: OnceCell<Tgt>,
+}
+
+impl<Src, Tgt> Lazy<Src, Tgt>
+where
+ Src: Eval<Tgt>,
+{
+ /// Creates a new lazy value with the given initializing value.
+ pub fn new(src: Src) -> Self {
+ Lazy {
+ src: Cell::new(Some(src)),
+ tgt: OnceCell::new(),
+ }
+ }
+ /// Creates a new lazy value with the given already-initialized value.
+ pub fn new_completed(tgt: Tgt) -> Self {
+ let lazy = Lazy {
+ src: Cell::new(None),
+ tgt: OnceCell::new(),
+ };
+ let _ = lazy.tgt.set(tgt);
+ lazy
+ }
+}
+
+impl<Src, Tgt> Deref for Lazy<Src, Tgt>
+where
+ Src: Eval<Tgt>,
+{
+ type Target = Tgt;
+ fn deref(&self) -> &Self::Target {
+ self.tgt.get_or_init(|| {
+ let src = self.src.take().unwrap();
+ src.eval()
+ })
+ }
+}
+
+impl<Src, Tgt> Debug for Lazy<Src, Tgt>
+where
+ Tgt: Debug,
+{
+ fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+ if let Some(tgt) = self.tgt.get() {
+ fmt.debug_tuple("Lazy@Init").field(tgt).finish()
+ } else {
+ fmt.debug_tuple("Lazy@Uninit").finish()
+ }
+ }
+}
diff --git a/dhall/src/semantics/nze/mod.rs b/dhall/src/semantics/nze/mod.rs
index 3d9c5eb..2c8d907 100644
--- a/dhall/src/semantics/nze/mod.rs
+++ b/dhall/src/semantics/nze/mod.rs
@@ -1,4 +1,5 @@
pub mod env;
+pub mod lazy;
pub mod normalize;
pub mod value;
pub mod var;
diff --git a/dhall/src/semantics/nze/value.rs b/dhall/src/semantics/nze/value.rs
index de40d53..ae06942 100644
--- a/dhall/src/semantics/nze/value.rs
+++ b/dhall/src/semantics/nze/value.rs
@@ -1,9 +1,8 @@
-use once_cell::unsync::OnceCell;
-use std::cell::RefCell;
use std::collections::HashMap;
use std::rc::Rc;
use crate::error::{TypeError, TypeMessage};
+use crate::semantics::nze::lazy;
use crate::semantics::Binder;
use crate::semantics::{
apply_any, normalize_one_layer, normalize_tyexpr_whnf, squash_textlit,
@@ -26,10 +25,7 @@ pub(crate) struct Value(Rc<ValueInternal>);
#[derive(Debug)]
struct ValueInternal {
- /// Exactly one of `thunk` of `kind` must be set at a given time.
- /// Once `thunk` is unset and `kind` is set, we never go back.
- thunk: RefCell<Option<Thunk>>,
- kind: OnceCell<ValueKind>,
+ kind: lazy::Lazy<Thunk, ValueKind>,
/// This is None if and only if `form` is `Sort` (which doesn't have a type)
ty: Option<Value>,
span: Span,
@@ -367,19 +363,15 @@ impl Value {
impl ValueInternal {
fn from_whnf(k: ValueKind, ty: Option<Value>, span: Span) -> Self {
- let kind = OnceCell::new();
- kind.set(k).unwrap();
ValueInternal {
- thunk: RefCell::new(None),
- kind,
+ kind: lazy::Lazy::new_completed(k),
ty,
span,
}
}
fn from_thunk(th: Thunk, ty: Option<Value>, span: Span) -> Self {
ValueInternal {
- thunk: RefCell::new(Some(th)),
- kind: OnceCell::new(),
+ kind: lazy::Lazy::new(th),
ty,
span,
}
@@ -389,21 +381,13 @@ impl ValueInternal {
}
fn kind(&self) -> &ValueKind {
- if self.kind.get().is_none() {
- let thunk = self.thunk.borrow_mut().take().unwrap();
- self.kind.set(thunk.eval()).unwrap();
- }
- self.kind.get().unwrap()
+ &self.kind
}
fn normalize(&self) {
self.kind().normalize();
}
- // Avoids a RefCell lock
+ // TODO: deprecated
fn normalize_mut(&mut self) {
- if self.kind.get().is_none() {
- let thunk = RefCell::get_mut(&mut self.thunk).take().unwrap();
- self.kind.set(thunk.eval()).unwrap();
- }
self.normalize();
}
@@ -622,6 +606,12 @@ impl TextLit {
}
}
+impl lazy::Eval<ValueKind> for Thunk {
+ fn eval(self) -> ValueKind {
+ self.eval()
+ }
+}
+
/// Compare two values for equality modulo alpha/beta-equivalence.
impl std::cmp::PartialEq for Value {
fn eq(&self, other: &Self) -> bool {
@@ -650,19 +640,12 @@ impl std::cmp::Eq for Closure {}
impl std::fmt::Debug for Value {
fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let vint: &ValueInternal = &self.0;
- let mut x = if let Some(kind) = vint.kind.get() {
- if let ValueKind::Const(c) = kind {
- return write!(fmt, "{:?}", c);
- } else {
- let mut x = fmt.debug_struct(&format!("Value@WHNF"));
- x.field("kind", kind);
- x
- }
- } else {
- let mut x = fmt.debug_struct(&format!("Value@Thunk"));
- x.field("thunk", vint.thunk.borrow().as_ref().unwrap());
- x
- };
+ let kind = vint.kind();
+ if let ValueKind::Const(c) = kind {
+ return write!(fmt, "{:?}", c);
+ }
+ let mut x = fmt.debug_struct(&format!("Value@WHNF"));
+ x.field("kind", kind);
if let Some(ty) = vint.ty.as_ref() {
x.field("type", &ty);
} else {