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Diffstat (limited to 'dhall/src/semantics/core/value.rs')
| -rw-r--r-- | dhall/src/semantics/core/value.rs | 338 |
1 files changed, 338 insertions, 0 deletions
diff --git a/dhall/src/semantics/core/value.rs b/dhall/src/semantics/core/value.rs new file mode 100644 index 0000000..bd7a9b9 --- /dev/null +++ b/dhall/src/semantics/core/value.rs @@ -0,0 +1,338 @@ +use std::cell::{Ref, RefCell, RefMut}; +use std::rc::Rc; + +use crate::syntax::{Builtin, Const, Span}; + +use crate::core::context::TypecheckContext; +use crate::core::valuef::ValueF; +use crate::core::var::{AlphaVar, Shift, Subst}; +use crate::error::{TypeError, TypeMessage}; +use crate::phase::normalize::{apply_any, normalize_whnf}; +use crate::phase::typecheck::{builtin_to_value, const_to_value}; +use crate::phase::{NormalizedExpr, Typed}; + +#[derive(Debug, Clone, Copy)] +pub(crate) enum Form { + /// No constraints; expression may not be normalized at all. + Unevaled, + /// Weak Head Normal Form, i.e. normalized up to the first constructor, but subexpressions may + /// not be normalized. This means that the first constructor of the contained ValueF is the first + /// constructor of the final Normal Form (NF). + WHNF, + /// Normal Form, i.e. completely normalized. + /// When all the Values in a ValueF are at least in WHNF, and recursively so, then the + /// ValueF is in NF. This is because WHNF ensures that we have the first constructor of the NF; so + /// if we have the first constructor of the NF at all levels, we actually have the NF. + NF, +} +use Form::{Unevaled, NF, WHNF}; + +/// Partially normalized value. +/// Invariant: if `form` is `WHNF`, `value` must be in Weak Head Normal Form +/// Invariant: if `form` is `NF`, `value` must be fully normalized +#[derive(Debug)] +struct ValueInternal { + form: Form, + value: ValueF, + /// This is None if and only if `value` is `Sort` (which doesn't have a type) + ty: Option<Value>, + span: Span, +} + +/// Stores a possibly unevaluated value. Gets (partially) normalized on-demand, +/// sharing computation automatically. Uses a RefCell to share computation. +/// Can optionally store a type from typechecking to preserve type information. +#[derive(Clone)] +pub(crate) struct Value(Rc<RefCell<ValueInternal>>); + +#[derive(Copy, Clone)] +/// Controls conversion from `Value` to `Expr` +pub(crate) struct ToExprOptions { + /// Whether to convert all variables to `_` + pub(crate) alpha: bool, + /// Whether to normalize before converting + pub(crate) normalize: bool, +} + +impl ValueInternal { + fn into_value(self) -> Value { + Value(Rc::new(RefCell::new(self))) + } + fn as_valuef(&self) -> &ValueF { + &self.value + } + + fn normalize_whnf(&mut self) { + take_mut::take_or_recover( + self, + // Dummy value in case the other closure panics + || ValueInternal { + form: Unevaled, + value: ValueF::Const(Const::Type), + ty: None, + span: Span::Artificial, + }, + |vint| match (&vint.form, &vint.ty) { + (Unevaled, Some(ty)) => ValueInternal { + form: WHNF, + value: normalize_whnf(vint.value, &ty), + ty: vint.ty, + span: vint.span, + }, + // `value` is `Sort` + (Unevaled, None) => ValueInternal { + form: NF, + value: ValueF::Const(Const::Sort), + ty: None, + span: vint.span, + }, + // Already in WHNF + (WHNF, _) | (NF, _) => vint, + }, + ) + } + fn normalize_nf(&mut self) { + match self.form { + Unevaled => { + self.normalize_whnf(); + self.normalize_nf(); + } + WHNF => { + self.value.normalize_mut(); + self.form = NF; + } + // Already in NF + NF => {} + } + } + + fn get_type(&self) -> Result<&Value, TypeError> { + match &self.ty { + Some(t) => Ok(t), + None => { + Err(TypeError::new(&TypecheckContext::new(), TypeMessage::Sort)) + } + } + } +} + +impl Value { + fn new(value: ValueF, form: Form, ty: Value, span: Span) -> Value { + ValueInternal { + form, + value, + ty: Some(ty), + span, + } + .into_value() + } + pub(crate) fn const_sort() -> Value { + ValueInternal { + form: NF, + value: ValueF::Const(Const::Sort), + ty: None, + span: Span::Artificial, + } + .into_value() + } + pub(crate) fn from_valuef_and_type(v: ValueF, t: Value) -> Value { + Value::new(v, Unevaled, t, Span::Artificial) + } + pub(crate) fn from_valuef_and_type_and_span( + v: ValueF, + t: Value, + span: Span, + ) -> Value { + Value::new(v, Unevaled, t, span) + } + pub(crate) fn from_valuef_and_type_whnf(v: ValueF, t: Value) -> Value { + Value::new(v, WHNF, t, Span::Artificial) + } + pub(crate) fn from_const(c: Const) -> Self { + const_to_value(c) + } + pub(crate) fn from_builtin(b: Builtin) -> Self { + builtin_to_value(b) + } + pub(crate) fn with_span(self, span: Span) -> Self { + self.as_internal_mut().span = span; + self + } + + pub(crate) fn as_const(&self) -> Option<Const> { + match &*self.as_whnf() { + ValueF::Const(c) => Some(*c), + _ => None, + } + } + pub(crate) fn span(&self) -> Span { + self.as_internal().span.clone() + } + + fn as_internal(&self) -> Ref<ValueInternal> { + self.0.borrow() + } + fn as_internal_mut(&self) -> RefMut<ValueInternal> { + self.0.borrow_mut() + } + /// WARNING: The returned ValueF may be entirely unnormalized, in aprticular it may just be an + /// unevaled PartialExpr. You probably want to use `as_whnf`. + fn as_valuef(&self) -> Ref<ValueF> { + Ref::map(self.as_internal(), ValueInternal::as_valuef) + } + /// 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 as_whnf(&self) -> Ref<ValueF> { + self.normalize_whnf(); + self.as_valuef() + } + + pub(crate) fn to_expr(&self, opts: ToExprOptions) -> NormalizedExpr { + if opts.normalize { + self.normalize_whnf(); + } + self.as_valuef().to_expr(opts) + } + pub(crate) fn to_whnf_ignore_type(&self) -> ValueF { + self.as_whnf().clone() + } + /// Before discarding type information, check that it matches the expected return type. + pub(crate) fn to_whnf_check_type(&self, ty: &Value) -> ValueF { + self.check_type(ty); + self.to_whnf_ignore_type() + } + pub(crate) fn into_typed(self) -> Typed { + Typed::from_value(self) + } + + /// Mutates the contents. If no one else shares this, this avoids a RefCell lock. + fn mutate_internal(&mut self, f: impl FnOnce(&mut ValueInternal)) { + match Rc::get_mut(&mut self.0) { + // Mutate directly if sole owner + Some(refcell) => f(RefCell::get_mut(refcell)), + // Otherwise mutate through the refcell + None => f(&mut self.as_internal_mut()), + } + } + /// Normalizes contents to normal form; faster than `normalize_nf` if + /// no one else shares this. + pub(crate) fn normalize_mut(&mut self) { + self.mutate_internal(|vint| vint.normalize_nf()) + } + + pub(crate) fn normalize_whnf(&self) { + let borrow = self.as_internal(); + match borrow.form { + Unevaled => { + drop(borrow); + self.as_internal_mut().normalize_whnf(); + } + // Already at least in WHNF + WHNF | NF => {} + } + } + + pub(crate) fn app(&self, v: Value) -> Value { + let body_t = match &*self.get_type_not_sort().as_whnf() { + ValueF::Pi(x, t, e) => { + v.check_type(t); + e.subst_shift(&x.into(), &v) + } + _ => unreachable!("Internal type error"), + }; + Value::from_valuef_and_type_whnf( + apply_any(self.clone(), v, &body_t), + body_t, + ) + } + + /// In debug mode, panic if the provided type doesn't match the value's type. + /// Otherwise does nothing. + pub(crate) fn check_type(&self, ty: &Value) { + debug_assert_eq!( + Some(ty), + self.get_type().ok().as_ref(), + "Internal type error" + ); + } + pub(crate) fn get_type(&self) -> Result<Value, TypeError> { + Ok(self.as_internal().get_type()?.clone()) + } + /// When we know the value isn't `Sort`, this gets the type directly + pub(crate) fn get_type_not_sort(&self) -> Value { + self.get_type() + .expect("Internal type error: value is `Sort` but shouldn't be") + } +} + +impl Shift for Value { + fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> { + Some(Value(self.0.shift(delta, var)?)) + } +} + +impl Shift for ValueInternal { + fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> { + Some(ValueInternal { + form: self.form, + value: self.value.shift(delta, var)?, + ty: self.ty.shift(delta, var)?, + span: self.span.clone(), + }) + } +} + +impl Subst<Value> for Value { + fn subst_shift(&self, var: &AlphaVar, val: &Value) -> Self { + match &*self.as_valuef() { + // If the var matches, we can just reuse the provided value instead of copying it. + // We also check that the types match, if in debug mode. + ValueF::Var(v) if v == var => { + if let Ok(self_ty) = self.get_type() { + val.check_type(&self_ty.subst_shift(var, val)); + } + val.clone() + } + _ => Value(self.0.subst_shift(var, val)), + } + } +} + +impl Subst<Value> for ValueInternal { + fn subst_shift(&self, var: &AlphaVar, val: &Value) -> Self { + ValueInternal { + // The resulting value may not stay in wnhf after substitution + form: Unevaled, + value: self.value.subst_shift(var, val), + ty: self.ty.subst_shift(var, val), + span: self.span.clone(), + } + } +} + +// TODO: use Rc comparison to shortcut on identical pointers +impl std::cmp::PartialEq for Value { + fn eq(&self, other: &Self) -> bool { + *self.as_whnf() == *other.as_whnf() + } +} +impl std::cmp::Eq for Value {} + +impl std::fmt::Debug for Value { + fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + let vint: &ValueInternal = &self.as_internal(); + if let ValueF::Const(c) = &vint.value { + write!(fmt, "{:?}", c) + } else { + let mut x = fmt.debug_struct(&format!("Value@{:?}", &vint.form)); + x.field("value", &vint.value); + if let Some(ty) = vint.ty.as_ref() { + x.field("type", &ty); + } else { + x.field("type", &None::<()>); + } + x.finish() + } + } +} |