diff options
Diffstat (limited to 'dhall/src')
| -rw-r--r-- | dhall/src/semantics/nze/value.rs | 159 |
1 files changed, 71 insertions, 88 deletions
diff --git a/dhall/src/semantics/nze/value.rs b/dhall/src/semantics/nze/value.rs index 87ebfcd..d25e8b5 100644 --- a/dhall/src/semantics/nze/value.rs +++ b/dhall/src/semantics/nze/value.rs @@ -25,22 +25,15 @@ pub(crate) struct Value(Rc<ValueInternal>); #[derive(Debug)] struct ValueInternal { - form: RefCell<Form>, + /// 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: RefCell<Option<ValueKind>>, /// This is None if and only if `form` is `Sort` (which doesn't have a type) ty: Option<Value>, span: Span, } -/// A potentially un-evaluated expression. Once we get to WHNF we won't modify the form again, as -/// explained in the doc for `ValueKind`. -#[derive(Debug, Clone)] -pub(crate) enum Form { - /// An unevaluated value. - Thunk(Thunk), - /// A value in WHNF. - WHNF(ValueKind), -} - /// An unevaluated subexpression #[derive(Debug, Clone)] pub(crate) enum Thunk { @@ -120,12 +113,9 @@ pub(crate) enum ValueKind { } impl Value { - fn new(form: Form, ty: Value, span: Span) -> Value { - ValueInternal::new(form, Some(ty), span).into_value() - } pub(crate) fn const_sort() -> Value { - ValueInternal::new( - Form::WHNF(ValueKind::Const(Const::Sort)), + ValueInternal::from_whnf( + ValueKind::Const(Const::Sort), None, Span::Artificial, ) @@ -133,8 +123,8 @@ impl Value { } /// Construct a Value from a completely unnormalized expression. pub(crate) fn new_thunk(env: &NzEnv, tye: TyExpr) -> Value { - ValueInternal::new( - Form::Thunk(Thunk::new(env, tye.clone())), + ValueInternal::from_thunk( + Thunk::new(env, tye.clone()), tye.get_type().ok(), tye.span().clone(), ) @@ -147,15 +137,16 @@ impl Value { ) -> Value { // TODO: env let env = NzEnv::new(); - Value::new( - Form::Thunk(Thunk::from_partial_expr(env, e, ty.clone())), - ty, + ValueInternal::from_thunk( + Thunk::from_partial_expr(env, e, ty.clone()), + Some(ty), Span::Artificial, ) + .into_value() } /// Make a Value from a ValueKind pub(crate) fn from_kind_and_type(v: ValueKind, t: Value) -> Value { - Value::new(Form::WHNF(v), t, Span::Artificial) + ValueInternal::from_whnf(v, Some(t), Span::Artificial).into_value() } pub(crate) fn from_const(c: Const) -> Self { let v = ValueKind::Const(c); @@ -189,18 +180,11 @@ impl Value { self.0.span.clone() } - fn as_form(&self) -> Ref<Form> { - self.0.form.borrow() - } /// This is what you want if you want to pattern-match on the value. /// WARNING: drop this ref before normalizing the same value or you will run into BorrowMut /// panics. pub(crate) fn kind(&self) -> Ref<ValueKind> { - self.normalize_whnf(); - Ref::map(self.as_form(), |form| match form { - Form::Thunk(..) => unreachable!(), - Form::WHNF(k) => k, - }) + self.0.kind() } /// Converts a value back to the corresponding AST expression. @@ -220,24 +204,16 @@ impl Value { self.to_whnf_ignore_type() } - /// Mutates the contents. If no one else shares this, this avoids a RefCell lock. - fn mutate_form(&mut self, f: impl FnOnce(&mut Form)) { + /// Normalizes contents to normal form; faster than `normalize_nf` if + /// no one else shares this. + pub(crate) fn normalize_mut(&mut self) { match Rc::get_mut(&mut self.0) { // Mutate directly if sole owner - Some(vint) => f(RefCell::get_mut(&mut vint.form)), + Some(vint) => vint.normalize_nf_mut(), // Otherwise mutate through the refcell - None => f(&mut self.0.form.borrow_mut()), + None => self.0.normalize_nf(), } } - /// Normalizes contents to normal form; faster than `normalize_nf` if - /// no one else shares this. - pub(crate) fn normalize_mut(&mut self) { - self.mutate_form(|form| form.normalize_nf()) - } - - pub(crate) fn normalize_whnf(&self) { - self.0.normalize_whnf() - } pub(crate) fn normalize_nf(&self) { self.0.normalize_nf() } @@ -389,9 +365,18 @@ impl Value { } impl ValueInternal { - fn new(form: Form, ty: Option<Value>, span: Span) -> Self { + fn from_whnf(k: ValueKind, ty: Option<Value>, span: Span) -> Self { ValueInternal { - form: RefCell::new(form), + thunk: RefCell::new(None), + kind: RefCell::new(Some(k)), + ty, + span, + } + } + fn from_thunk(th: Thunk, ty: Option<Value>, span: Span) -> Self { + ValueInternal { + kind: RefCell::new(None), + thunk: RefCell::new(Some(th)), ty, span, } @@ -400,13 +385,38 @@ impl ValueInternal { Value(Rc::new(self)) } + fn kind(&self) -> Ref<ValueKind> { + self.normalize_whnf(); + Ref::map(self.kind.borrow(), |kind| kind.as_ref().unwrap()) + } fn normalize_whnf(&self) { - if !self.form.borrow().is_whnf() { - self.form.borrow_mut().normalize_whnf() + if self.kind.borrow().is_none() { + let mut thunk_borrow = self.thunk.borrow_mut(); + let kind = thunk_borrow.as_ref().unwrap().eval(); + *thunk_borrow = None; + *self.kind.borrow_mut() = Some(kind); } } fn normalize_nf(&self) { - self.form.borrow_mut().normalize_nf() + self.normalize_whnf(); + self.kind.borrow_mut().as_mut().unwrap().normalize_mut() + } + // Avoids a RefCell lock + fn normalize_whnf_mut(&mut self) { + let self_thunk = RefCell::get_mut(&mut self.thunk); + if let Some(thunk) = &mut *self_thunk { + let self_kind = RefCell::get_mut(&mut self.kind); + let mut kind = thunk.eval(); + kind.normalize_mut(); + *self_kind = Some(kind); + *self_thunk = None; + } + } + // Avoids a RefCell lock + fn normalize_nf_mut(&mut self) { + self.normalize_whnf_mut(); + let self_kind = RefCell::get_mut(&mut self.kind); + self_kind.as_mut().unwrap().normalize_mut(); } fn get_type(&self) -> Result<&Value, TypeError> { @@ -417,33 +427,6 @@ impl ValueInternal { } } -impl Form { - fn is_whnf(&self) -> bool { - match self { - Form::Thunk(..) => false, - Form::WHNF(..) => true, - } - } - fn normalize_whnf(&mut self) { - use std::mem::replace; - let dummy = Form::WHNF(ValueKind::Const(Const::Type)); - *self = match replace(self, dummy) { - Form::Thunk(th) => Form::WHNF(th.eval()), - // Already in WHNF - form @ Form::WHNF(_) => form, - }; - } - fn normalize_nf(&mut self) { - if !self.is_whnf() { - self.normalize_whnf(); - } - match self { - Form::Thunk(..) => unreachable!(), - Form::WHNF(k) => k.normalize_mut(), - } - } -} - impl ValueKind { pub(crate) fn into_value_with_type(self, t: Value) -> Value { Value::from_kind_and_type(self, t) @@ -687,21 +670,21 @@ 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 = match &*vint.form.borrow() { - Form::Thunk(th) => { - let mut x = fmt.debug_struct(&format!("Value@Thunk")); - x.field("thunk", th); + let kind_borrow = vint.kind.borrow(); + let mut x = if let Some(kind) = kind_borrow.as_ref() { + 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 } - Form::WHNF(kind) => { - 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 thunk_borrow = vint.thunk.borrow(); + let th = thunk_borrow.as_ref().unwrap(); + let mut x = fmt.debug_struct(&format!("Value@Thunk")); + x.field("thunk", th); + x }; if let Some(ty) = vint.ty.as_ref() { x.field("type", &ty); |