diff options
Diffstat (limited to '')
-rw-r--r-- | dhall/src/core/var.rs | 35 |
1 files changed, 31 insertions, 4 deletions
diff --git a/dhall/src/core/var.rs b/dhall/src/core/var.rs index 296e968..3af12ec 100644 --- a/dhall/src/core/var.rs +++ b/dhall/src/core/var.rs @@ -50,8 +50,8 @@ pub(crate) trait Shift: Sized { } } -pub(crate) trait Subst<T> { - fn subst_shift(&self, var: &AlphaVar, val: &T) -> Self; +pub(crate) trait Subst<S> { + fn subst_shift(&self, var: &AlphaVar, val: &S) -> Self; } impl AlphaVar { @@ -98,8 +98,35 @@ impl Shift for () { } } -impl<T> Subst<T> for () { - fn subst_shift(&self, _var: &AlphaVar, _val: &T) -> Self {} +impl<T: Shift> Shift for Option<T> { + fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> { + Some(match self { + None => None, + Some(x) => Some(x.shift(delta, var)?), + }) + } +} + +impl<T: Shift> Shift for Box<T> { + fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> { + Some(Box::new(self.as_ref().shift(delta, var)?)) + } +} + +impl<S> Subst<S> for () { + fn subst_shift(&self, _var: &AlphaVar, _val: &S) -> Self {} +} + +impl<S, T: Subst<S>> Subst<S> for Option<T> { + fn subst_shift(&self, var: &AlphaVar, val: &S) -> Self { + self.as_ref().map(|x| x.subst_shift(var, val)) + } +} + +impl<S, T: Subst<S>> Subst<S> for Box<T> { + fn subst_shift(&self, var: &AlphaVar, val: &S) -> Self { + Box::new(self.as_ref().subst_shift(var, val)) + } } /// Equality up to alpha-equivalence |