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-rw-r--r--dhall/src/core/context.rs65
-rw-r--r--dhall/src/core/thunk.rs40
-rw-r--r--dhall/src/core/value.rs121
-rw-r--r--dhall/src/core/var.rs39
-rw-r--r--dhall/src/error/mod.rs1
-rw-r--r--dhall/src/lib.rs1
-rw-r--r--dhall/src/phase/mod.rs18
-rw-r--r--dhall/src/phase/typecheck.rs13
-rw-r--r--dhall_syntax/src/core/expr.rs22
9 files changed, 182 insertions, 138 deletions
diff --git a/dhall/src/core/context.rs b/dhall/src/core/context.rs
index 236bebe..328bfdc 100644
--- a/dhall/src/core/context.rs
+++ b/dhall/src/core/context.rs
@@ -33,7 +33,7 @@ impl<T> Context<T> {
T: Shift + Clone,
{
let mut vec = self.0.as_ref().clone();
- vec.push((x.clone(), CtxItem::Kept(x.into(), t.shift(1, &x.into()))));
+ vec.push((x.clone(), CtxItem::Kept(x.into(), t.under_binder(x))));
Context(Rc::new(vec))
}
pub(crate) fn insert_replaced(&self, x: &Label, th: Thunk, t: T) -> Self
@@ -51,11 +51,10 @@ impl<T> Context<T> {
let mut var = var.clone();
let mut shift_map: HashMap<Label, _> = HashMap::new();
for (l, i) in self.0.iter().rev() {
- if var == l.into() {
- return Ok(i.shift0_multiple(&shift_map));
- } else {
- var = var.shift(-1, &l.into());
- }
+ match var.over_binder(l) {
+ None => return Ok(i.under_multiple_binders(&shift_map)),
+ Some(newvar) => var = newvar,
+ };
if let CtxItem::Kept(_, _) = i {
*shift_map.entry(l.clone()).or_insert(0) += 1;
}
@@ -67,11 +66,11 @@ impl<T> Context<T> {
/// that the passed variable always makes sense in the context of the passed item.
/// Once we pass the variable definition, the variable doesn't make sense anymore so we just
/// copy the remaining items.
- fn do_with_var(
+ fn do_with_var<E>(
&self,
var: &AlphaVar,
- mut f: impl FnMut(&AlphaVar, &CtxItem<T>) -> CtxItem<T>,
- ) -> Self
+ mut f: impl FnMut(&AlphaVar, &CtxItem<T>) -> Result<CtxItem<T>, E>,
+ ) -> Result<Self, E>
where
T: Clone,
{
@@ -80,32 +79,32 @@ impl<T> Context<T> {
let mut var = var.clone();
let mut iter = self.0.iter().rev();
for (l, i) in iter.by_ref() {
- vec.push((l.clone(), f(&var, i)));
+ vec.push((l.clone(), f(&var, i)?));
if let CtxItem::Kept(_, _) = i {
- if var == l.into() {
- break;
- } else {
- var = var.shift(-1, &l.into());
- }
+ match var.over_binder(l) {
+ None => break,
+ Some(newvar) => var = newvar,
+ };
}
}
for (l, i) in iter {
vec.push((l.clone(), (*i).clone()));
}
vec.reverse();
- Context(Rc::new(vec))
+ Ok(Context(Rc::new(vec)))
}
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self>
where
T: Clone + Shift,
{
- self.do_with_var(var, |var, i| i.shift(delta, &var))
+ Some(self.do_with_var(var, |var, i| Ok(i.shift(delta, &var)?))?)
}
fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self
where
T: Clone + Subst<Typed>,
{
- self.do_with_var(var, |var, i| i.subst_shift(&var, val))
+ self.do_with_var(var, |var, i| Ok::<_, !>(i.subst_shift(&var, val)))
+ .unwrap()
}
}
@@ -158,27 +157,27 @@ impl TypecheckContext {
}
impl<T: Shift> Shift for CtxItem<T> {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
- match self {
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
+ Some(match self {
CtxItem::Kept(v, t) => {
- CtxItem::Kept(v.shift(delta, var), t.shift(delta, var))
+ CtxItem::Kept(v.shift(delta, var)?, t.shift(delta, var)?)
}
CtxItem::Replaced(e, t) => {
- CtxItem::Replaced(e.shift(delta, var), t.shift(delta, var))
+ CtxItem::Replaced(e.shift(delta, var)?, t.shift(delta, var)?)
}
- }
+ })
}
}
impl<T: Clone + Shift> Shift for Context<T> {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
self.shift(delta, var)
}
}
impl Shift for NormalizationContext {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
- NormalizationContext(self.0.shift(delta, var))
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
+ Some(NormalizationContext(self.0.shift(delta, var)?))
}
}
@@ -189,12 +188,12 @@ impl<T: Subst<Typed>> Subst<Typed> for CtxItem<T> {
e.subst_shift(var, val),
t.subst_shift(var, val),
),
- CtxItem::Kept(v, t) if v == var => {
- CtxItem::Replaced(val.to_thunk(), t.subst_shift(var, val))
- }
- CtxItem::Kept(v, t) => {
- CtxItem::Kept(v.shift(-1, var), t.subst_shift(var, val))
- }
+ CtxItem::Kept(v, t) => match v.shift(-1, var) {
+ None => {
+ CtxItem::Replaced(val.to_thunk(), t.subst_shift(var, val))
+ }
+ Some(newvar) => CtxItem::Kept(newvar, t.subst_shift(var, val)),
+ },
}
}
}
diff --git a/dhall/src/core/thunk.rs b/dhall/src/core/thunk.rs
index a02d7ae..51922e1 100644
--- a/dhall/src/core/thunk.rs
+++ b/dhall/src/core/thunk.rs
@@ -264,38 +264,38 @@ impl TypeThunk {
}
impl Shift for Thunk {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
- self.0.borrow().shift(delta, var).into_thunk()
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
+ Some(self.0.borrow().shift(delta, var)?.into_thunk())
}
}
impl Shift for ThunkInternal {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
- match self {
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
+ Some(match self {
ThunkInternal::Unnormalized(ctx, e) => {
- ThunkInternal::Unnormalized(ctx.shift(delta, var), e.clone())
+ ThunkInternal::Unnormalized(ctx.shift(delta, var)?, e.clone())
}
ThunkInternal::PartialExpr(e) => ThunkInternal::PartialExpr(
- e.map_ref_with_special_handling_of_binders(
- |v| v.shift(delta, var),
- |x, v| v.shift(delta, &var.shift(1, &x.into())),
- X::clone,
- Label::clone,
- ),
+ e.traverse_ref_with_special_handling_of_binders(
+ |v| Ok(v.shift(delta, var)?),
+ |x, v| Ok(v.shift(delta, &var.under_binder(x))?),
+ |x| Ok(X::clone(x)),
+ |l| Ok(Label::clone(l)),
+ )?,
),
ThunkInternal::Value(m, v) => {
- ThunkInternal::Value(*m, v.shift(delta, var))
+ ThunkInternal::Value(*m, v.shift(delta, var)?)
}
- }
+ })
}
}
impl Shift for TypeThunk {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
- match self {
- TypeThunk::Thunk(th) => TypeThunk::Thunk(th.shift(delta, var)),
- TypeThunk::Type(t) => TypeThunk::Type(t.shift(delta, var)),
- }
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
+ Some(match self {
+ TypeThunk::Thunk(th) => TypeThunk::Thunk(th.shift(delta, var)?),
+ TypeThunk::Type(t) => TypeThunk::Type(t.shift(delta, var)?),
+ })
}
}
@@ -317,8 +317,8 @@ impl Subst<Typed> for ThunkInternal {
|v| v.subst_shift(var, val),
|x, v| {
v.subst_shift(
- &var.shift(1, &x.into()),
- &val.shift(1, &x.into()),
+ &var.under_binder(x),
+ &val.under_binder(x),
)
},
X::clone,
diff --git a/dhall/src/core/value.rs b/dhall/src/core/value.rs
index 8fa24c7..e91b6bc 100644
--- a/dhall/src/core/value.rs
+++ b/dhall/src/core/value.rs
@@ -98,14 +98,14 @@ impl Value {
}
Value::ListConsClosure(a, None) => {
// Avoid accidental capture of the new `x` variable
- let a1 = a.shift(1, &Label::from("x").into());
+ let a1 = a.under_binder(Label::from("x"));
let a1 = a1.normalize_to_expr_maybe_alpha(alpha);
let a = a.normalize_to_expr_maybe_alpha(alpha);
dhall::subexpr!(λ(x : a) -> λ(xs : List a1) -> [ x ] # xs)
}
Value::ListConsClosure(n, Some(v)) => {
// Avoid accidental capture of the new `xs` variable
- let v = v.shift(1, &Label::from("xs").into());
+ let v = v.under_binder(Label::from("xs"));
let v = v.normalize_to_expr_maybe_alpha(alpha);
let a = n.normalize_to_expr_maybe_alpha(alpha);
dhall::subexpr!(λ(xs : List a) -> [ v ] # xs)
@@ -322,102 +322,121 @@ impl Value {
}
impl Shift for Value {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
- match self {
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
+ Some(match self {
Value::Lam(x, t, e) => Value::Lam(
x.clone(),
- t.shift(delta, var),
- e.shift(delta, &var.shift(1, &x.into())),
+ t.shift(delta, var)?,
+ e.shift(delta, &var.under_binder(x))?,
),
Value::AppliedBuiltin(b, args) => Value::AppliedBuiltin(
*b,
- args.iter().map(|v| v.shift(delta, var)).collect(),
+ args.iter()
+ .map(|v| Ok(v.shift(delta, var)?))
+ .collect::<Result<_, _>>()?,
),
Value::NaturalSuccClosure => Value::NaturalSuccClosure,
Value::OptionalSomeClosure(tth) => {
- Value::OptionalSomeClosure(tth.shift(delta, var))
+ Value::OptionalSomeClosure(tth.shift(delta, var)?)
}
Value::ListConsClosure(t, v) => Value::ListConsClosure(
- t.shift(delta, var),
- v.as_ref().map(|v| v.shift(delta, var)),
+ t.shift(delta, var)?,
+ v.as_ref().map(|v| Ok(v.shift(delta, var)?)).transpose()?,
),
Value::Pi(x, t, e) => Value::Pi(
x.clone(),
- t.shift(delta, var),
- e.shift(delta, &var.shift(1, &x.into())),
+ t.shift(delta, var)?,
+ e.shift(delta, &var.under_binder(x))?,
),
- Value::Var(v) => Value::Var(v.shift(delta, var)),
+ Value::Var(v) => Value::Var(v.shift(delta, var)?),
Value::Const(c) => Value::Const(*c),
Value::BoolLit(b) => Value::BoolLit(*b),
Value::NaturalLit(n) => Value::NaturalLit(*n),
Value::IntegerLit(n) => Value::IntegerLit(*n),
Value::DoubleLit(n) => Value::DoubleLit(*n),
Value::EmptyOptionalLit(tth) => {
- Value::EmptyOptionalLit(tth.shift(delta, var))
+ Value::EmptyOptionalLit(tth.shift(delta, var)?)
}
Value::NEOptionalLit(th) => {
- Value::NEOptionalLit(th.shift(delta, var))
+ Value::NEOptionalLit(th.shift(delta, var)?)
}
Value::EmptyListLit(tth) => {
- Value::EmptyListLit(tth.shift(delta, var))
+ Value::EmptyListLit(tth.shift(delta, var)?)
}
Value::NEListLit(elts) => Value::NEListLit(
- elts.iter().map(|v| v.shift(delta, var)).collect(),
+ elts.iter()
+ .map(|v| Ok(v.shift(delta, var)?))
+ .collect::<Result<_, _>>()?,
),
Value::RecordLit(kvs) => Value::RecordLit(
kvs.iter()
- .map(|(k, v)| (k.clone(), v.shift(delta, var)))
- .collect(),
+ .map(|(k, v)| Ok((k.clone(), v.shift(delta, var)?)))
+ .collect::<Result<_, _>>()?,
),
Value::RecordType(kvs) => Value::RecordType(
kvs.iter()
- .map(|(k, v)| (k.clone(), v.shift(delta, var)))
- .collect(),
+ .map(|(k, v)| Ok((k.clone(), v.shift(delta, var)?)))
+ .collect::<Result<_, _>>()?,
),
Value::UnionType(kts) => Value::UnionType(
kts.iter()
.map(|(k, v)| {
- (k.clone(), v.as_ref().map(|v| v.shift(delta, var)))
+ Ok((
+ k.clone(),
+ v.as_ref()
+ .map(|v| Ok(v.shift(delta, var)?))
+ .transpose()?,
+ ))
})
- .collect(),
+ .collect::<Result<_, _>>()?,
),
Value::UnionConstructor(x, kts) => Value::UnionConstructor(
x.clone(),
kts.iter()
.map(|(k, v)| {
- (k.clone(), v.as_ref().map(|v| v.shift(delta, var)))
+ Ok((
+ k.clone(),
+ v.as_ref()
+ .map(|v| Ok(v.shift(delta, var)?))
+ .transpose()?,
+ ))
})
- .collect(),
+ .collect::<Result<_, _>>()?,
),
Value::UnionLit(x, v, kts) => Value::UnionLit(
x.clone(),
- v.shift(delta, var),
+ v.shift(delta, var)?,
kts.iter()
.map(|(k, v)| {
- (k.clone(), v.as_ref().map(|v| v.shift(delta, var)))
+ Ok((
+ k.clone(),
+ v.as_ref()
+ .map(|v| Ok(v.shift(delta, var)?))
+ .transpose()?,
+ ))
})
- .collect(),
+ .collect::<Result<_, _>>()?,
),
Value::TextLit(elts) => Value::TextLit(
elts.iter()
.map(|contents| {
use InterpolatedTextContents::{Expr, Text};
- match contents {
- Expr(th) => Expr(th.shift(delta, var)),
+ Ok(match contents {
+ Expr(th) => Expr(th.shift(delta, var)?),
Text(s) => Text(s.clone()),
- }
+ })
})
- .collect(),
+ .collect::<Result<_, _>>()?,
),
- Value::PartialExpr(e) => {
- Value::PartialExpr(e.map_ref_with_special_handling_of_binders(
- |v| v.shift(delta, var),
- |x, v| v.shift(delta, &var.shift(1, &x.into())),
- X::clone,
- Label::clone,
- ))
- }
- }
+ Value::PartialExpr(e) => Value::PartialExpr(
+ e.traverse_ref_with_special_handling_of_binders(
+ |v| Ok(v.shift(delta, var)?),
+ |x, v| Ok(v.shift(delta, &var.under_binder(x))?),
+ |x| Ok(X::clone(x)),
+ |l| Ok(Label::clone(l)),
+ )?,
+ ),
+ })
}
}
@@ -435,8 +454,8 @@ impl Subst<Typed> for Value {
|v| v.subst_shift(var, val),
|x, v| {
v.subst_shift(
- &var.shift(1, &x.into()),
- &val.shift(1, &x.into()),
+ &var.under_binder(x),
+ &val.under_binder(x),
)
},
X::clone,
@@ -456,10 +475,7 @@ impl Subst<Typed> for Value {
Value::Lam(x, t, e) => Value::Lam(
x.clone(),
t.subst_shift(var, val),
- e.subst_shift(
- &var.shift(1, &x.into()),
- &val.shift(1, &x.into()),
- ),
+ e.subst_shift(&var.under_binder(x), &val.under_binder(x)),
),
Value::NaturalSuccClosure => Value::NaturalSuccClosure,
Value::OptionalSomeClosure(tth) => {
@@ -472,13 +488,12 @@ impl Subst<Typed> for Value {
Value::Pi(x, t, e) => Value::Pi(
x.clone(),
t.subst_shift(var, val),
- e.subst_shift(
- &var.shift(1, &x.into()),
- &val.shift(1, &x.into()),
- ),
+ e.subst_shift(&var.under_binder(x), &val.under_binder(x)),
),
- Value::Var(v) if v == var => val.to_value().clone(),
- Value::Var(v) => Value::Var(v.shift(-1, var)),
+ Value::Var(v) => match v.shift(-1, var) {
+ None => val.to_value().clone(),
+ Some(newvar) => Value::Var(newvar),
+ },
Value::Const(c) => Value::Const(*c),
Value::BoolLit(b) => Value::BoolLit(*b),
Value::NaturalLit(n) => Value::NaturalLit(*n),
diff --git a/dhall/src/core/var.rs b/dhall/src/core/var.rs
index ba92172..ea7e55f 100644
--- a/dhall/src/core/var.rs
+++ b/dhall/src/core/var.rs
@@ -17,19 +17,34 @@ pub(crate) struct AlphaVar {
pub(crate) struct AlphaLabel(Label);
pub(crate) trait Shift: Sized {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self;
+ // Shift an expression to move it around binders without changing the meaning of its free
+ // variables. Shift by 1 to move an expression under a binder. Shift by -1 to extract an
+ // expression from under a binder, if the expression does not refer to that bound variable.
+ // Returns None if delta was negative and the variable was free in the expression.
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self>;
- fn shift0(&self, delta: isize, x: &Label) -> Self {
- self.shift(delta, &x.into())
+ fn over_binder<T>(&self, x: T) -> Option<Self>
+ where
+ T: Into<AlphaVar>,
+ {
+ self.shift(-1, &x.into())
}
- fn shift0_multiple(&self, shift_map: &HashMap<Label, isize>) -> Self
+ fn under_binder<T>(&self, x: T) -> Self
+ where
+ T: Into<AlphaVar>,
+ {
+ // Can't fail since delta is positive
+ self.shift(1, &x.into()).unwrap()
+ }
+
+ fn under_multiple_binders(&self, shift_map: &HashMap<Label, usize>) -> Self
where
Self: Clone,
{
let mut v = self.clone();
for (x, n) in shift_map {
- v = v.shift0(*n, x);
+ v = v.shift(*n as isize, &x.into()).unwrap();
}
v
}
@@ -68,20 +83,20 @@ impl AlphaLabel {
}
impl Shift for AlphaVar {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
- AlphaVar {
- normal: self.normal.shift(delta, &var.normal),
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
+ Some(AlphaVar {
+ normal: self.normal.shift(delta, &var.normal)?,
alpha: match (&self.alpha, &var.alpha) {
- (Some(x), Some(v)) => Some(x.shift(delta, v)),
+ (Some(x), Some(v)) => Some(x.shift(delta, v)?),
_ => None,
},
- }
+ })
}
}
impl Shift for () {
- fn shift(&self, _delta: isize, _var: &AlphaVar) -> Self {
- ()
+ fn shift(&self, _delta: isize, _var: &AlphaVar) -> Option<Self> {
+ Some(())
}
}
diff --git a/dhall/src/error/mod.rs b/dhall/src/error/mod.rs
index ff748bc..3f482f6 100644
--- a/dhall/src/error/mod.rs
+++ b/dhall/src/error/mod.rs
@@ -69,6 +69,7 @@ pub(crate) enum TypeMessage {
MergeVariantMissingHandler(Label),
MergeAnnotMismatch,
MergeHandlerTypeMismatch,
+ MergeHandlerReturnTypeMustNotBeDependent,
ProjectionMustBeRecord,
ProjectionMissingEntry,
Sort,
diff --git a/dhall/src/lib.rs b/dhall/src/lib.rs
index 8d1496a..b35b2ae 100644
--- a/dhall/src/lib.rs
+++ b/dhall/src/lib.rs
@@ -6,6 +6,7 @@
#![feature(bind_by_move_pattern_guards)]
#![feature(try_trait)]
#![feature(inner_deref)]
+#![feature(never_type)]
#![cfg_attr(test, feature(custom_inner_attributes))]
#![allow(
clippy::type_complexity,
diff --git a/dhall/src/phase/mod.rs b/dhall/src/phase/mod.rs
index db0a2b9..50103a0 100644
--- a/dhall/src/phase/mod.rs
+++ b/dhall/src/phase/mod.rs
@@ -238,26 +238,26 @@ impl Normalized {
}
impl Shift for Typed {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
- match self {
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
+ Some(match self {
Typed::Value(th, t) => Typed::Value(
- th.shift(delta, var),
- t.as_ref().map(|x| x.shift(delta, var)),
+ th.shift(delta, var)?,
+ t.as_ref().map(|x| Ok(x.shift(delta, var)?)).transpose()?,
),
Typed::Const(c) => Typed::Const(*c),
- }
+ })
}
}
impl Shift for Type {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
- Type(Box::new(self.0.shift(delta, var)))
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
+ Some(Type(Box::new(self.0.shift(delta, var)?)))
}
}
impl Shift for Normalized {
- fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
- Normalized(self.0.shift(delta, var))
+ fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
+ Some(Normalized(self.0.shift(delta, var)?))
}
}
diff --git a/dhall/src/phase/typecheck.rs b/dhall/src/phase/typecheck.rs
index 2c625fb..497a703 100644
--- a/dhall/src/phase/typecheck.rs
+++ b/dhall/src/phase/typecheck.rs
@@ -732,6 +732,7 @@ fn type_last_layer(
)))
}
};
+
ensure_equal!(&variant_type, &tx, {
mkerr(TypeMismatch(
handler_type.to_typed(),
@@ -739,8 +740,16 @@ fn type_last_layer(
variant_type.to_typed(),
))
});
- // TODO: check that x is not free in tb first
- tb.shift(-1, &x.into())
+
+ // Extract `tb` from under the `x` binder. Fails is `x` was free in `tb`.
+ match tb.over_binder(x) {
+ Some(x) => x,
+ None => {
+ return Err(mkerr(
+ MergeHandlerReturnTypeMustNotBeDependent,
+ ))
+ }
+ }
}
// Union alternative without type
Some(None) => handler.to_type(ctx)?,
diff --git a/dhall_syntax/src/core/expr.rs b/dhall_syntax/src/core/expr.rs
index 4bfd224..1a33ed1 100644
--- a/dhall_syntax/src/core/expr.rs
+++ b/dhall_syntax/src/core/expr.rs
@@ -442,22 +442,26 @@ pub fn rc<E>(x: Expr<X, E>) -> SubExpr<X, E> {
/// Add an isize to an usize
/// Panics on over/underflow
-fn add_ui(u: usize, i: isize) -> usize {
- if i < 0 {
- u.checked_sub(i.checked_neg().unwrap() as usize).unwrap()
+fn add_ui(u: usize, i: isize) -> Option<usize> {
+ Some(if i < 0 {
+ u.checked_sub(i.checked_neg()? as usize)?
} else {
- u.checked_add(i as usize).unwrap()
- }
+ u.checked_add(i as usize)?
+ })
}
impl<Label: PartialEq + Clone> V<Label> {
- pub fn shift(&self, delta: isize, var: &V<Label>) -> Self {
+ pub fn shift(&self, delta: isize, var: &V<Label>) -> Option<Self> {
let V(x, n) = var;
let V(y, m) = self;
- if x == y && n <= m {
- V(y.clone(), add_ui(*m, delta))
+ Some(if x == y && n <= m {
+ V(y.clone(), add_ui(*m, delta)?)
} else {
V(y.clone(), *m)
- }
+ })
+ }
+
+ pub fn over_binder(&self, x: &Label) -> Option<Self> {
+ self.shift(-1, &V(x.clone(), 0))
}
}
generated by cgit v1.2.3 (git 2.25.1) at 2024-12-23 16:06:46 +0000