diff options
Diffstat (limited to '')
-rw-r--r-- | dhall_syntax/src/core/visitor.rs | 193 |
1 files changed, 54 insertions, 139 deletions
diff --git a/dhall_syntax/src/core/visitor.rs b/dhall_syntax/src/core/visitor.rs index 647f76f..f2f3b32 100644 --- a/dhall_syntax/src/core/visitor.rs +++ b/dhall_syntax/src/core/visitor.rs @@ -2,52 +2,56 @@ use crate::*; use std::iter::FromIterator; /// A way too generic Visitor trait. -pub trait GenericVisitor<Input, Return>: Sized { - fn visit(self, input: Input) -> Return; +pub trait GenericVisitor<Input, Output>: Sized { + fn visit(self, input: Input) -> Output; } -/// A visitor trait that can be used to traverse `ExprF`s. We need this pattern -/// so that Rust lets us have as much mutability as we can. -/// For example, `traverse_embed` cannot be made using only `traverse_ref`, because -/// `traverse_ref` takes a `FnMut` so we would need to pass multiple mutable -/// reverences to this argument to `traverse_ref`. But Rust's ownership system -/// is all about preventing exactly this ! So we have to be more clever. -/// The visitor pattern allows us to have only one mutable thing the whole -/// time: the visitor itself. The visitor can then carry around multiple closures -/// or just one, and Rust is ok with either. See for example TraverseRefVisitor -/// and TraverseEmbedVisitor. -/// This is very generic. For a more legible trait, see ExprFInFallibleVisitor -pub trait ExprFVeryGenericVisitor<'a, Ret, SE1, E1>: Sized { +/// A visitor trait that can be used to traverse `ExprF`s. We need this pattern so that Rust lets +/// us have as much mutability as we can. +/// For example, `traverse_ref_with_special_handling_of_binders` cannot be made using only +/// `traverse_ref`, because `traverse_ref` takes a `FnMut` so we would need to pass multiple +/// mutable reverences to this argument to `traverse_ref`. But Rust's ownership system is all about +/// preventing exactly this ! So we have to be more clever. The visitor pattern allows us to have +/// only one mutable thing the whole time: the visitor itself. The visitor can then carry around +/// multiple closures or just one, and Rust is ok with either. See for example TraverseRefVisitor. +pub trait ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>: Sized { type Error; - type SE2; - type E2; - fn visit_subexpr( - &mut self, - subexpr: &'a SE1, - ) -> Result<Self::SE2, Self::Error>; + fn visit_subexpr(&mut self, subexpr: &'a SE1) -> Result<SE2, Self::Error>; + fn visit_embed(self, embed: &'a E1) -> Result<E2, Self::Error>; fn visit_subexpr_under_binder( - self, - label: &'a Label, + mut self, + _label: &'a Label, subexpr: &'a SE1, - ) -> Result<Self::SE2, Self::Error>; + ) -> Result<SE2, Self::Error> { + self.visit_subexpr(subexpr) + } +} - fn visit_embed_squash(self, embed: &'a E1) -> Result<Ret, Self::Error>; +/// Like ExprFFallibleVisitor, but without the error handling. +pub trait ExprFInFallibleVisitor<'a, SE1, SE2, E1, E2>: Sized { + fn visit_subexpr(&mut self, subexpr: &'a SE1) -> SE2; + fn visit_embed(self, embed: &'a E1) -> E2; - // Called with the result of the map, in the non-embed case. - // Useful to change the result type, and/or avoid some loss of info - fn visit_resulting_exprf( - result: ExprF<Self::SE2, Self::E2>, - ) -> Result<Ret, Self::Error>; + fn visit_subexpr_under_binder( + mut self, + _label: &'a Label, + subexpr: &'a SE1, + ) -> SE2 { + self.visit_subexpr(subexpr) + } } -impl<'a, T, Ret, SE1, E1> - GenericVisitor<&'a ExprF<SE1, E1>, Result<Ret, T::Error>> for T +impl<'a, T, SE1, SE2, E1, E2> + GenericVisitor<&'a ExprF<SE1, E1>, Result<ExprF<SE2, E2>, T::Error>> for T where - T: ExprFVeryGenericVisitor<'a, Ret, SE1, E1>, + T: ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>, { - fn visit(self, input: &'a ExprF<SE1, E1>) -> Result<Ret, T::Error> { + fn visit( + self, + input: &'a ExprF<SE1, E1>, + ) -> Result<ExprF<SE2, E2>, T::Error> { fn vec<'a, T, U, Err, F: FnMut(&'a T) -> Result<U, Err>>( x: &'a [T], f: F, @@ -63,27 +67,27 @@ where None => None, }) } - fn dupmap<'a, V, Ret, SE, E, T>( - x: impl IntoIterator<Item = (&'a Label, &'a SE)>, + fn dupmap<'a, V, SE1, SE2, E1, E2, T>( + x: impl IntoIterator<Item = (&'a Label, &'a SE1)>, mut v: V, ) -> Result<T, V::Error> where - SE: 'a, - T: FromIterator<(Label, V::SE2)>, - V: ExprFVeryGenericVisitor<'a, Ret, SE, E>, + SE1: 'a, + T: FromIterator<(Label, SE2)>, + V: ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>, { x.into_iter() .map(|(k, x)| Ok((k.clone(), v.visit_subexpr(x)?))) .collect() } - fn optdupmap<'a, V, Ret, SE, E, T>( - x: impl IntoIterator<Item = (&'a Label, &'a Option<SE>)>, + fn optdupmap<'a, V, SE1, SE2, E1, E2, T>( + x: impl IntoIterator<Item = (&'a Label, &'a Option<SE1>)>, mut v: V, ) -> Result<T, V::Error> where - SE: 'a, - T: FromIterator<(Label, Option<V::SE2>)>, - V: ExprFVeryGenericVisitor<'a, Ret, SE, E>, + SE1: 'a, + T: FromIterator<(Label, Option<SE2>)>, + V: ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>, { x.into_iter() .map(|(k, x)| { @@ -100,7 +104,7 @@ where let mut v = self; use crate::ExprF::*; - T::visit_resulting_exprf(match input { + Ok(match input { Var(v) => Var(v.clone()), Lam(l, t, e) => { let t = v.visit_subexpr(t)?; @@ -149,90 +153,18 @@ where Field(e, l) => Field(v.visit_subexpr(e)?, l.clone()), Projection(e, ls) => Projection(v.visit_subexpr(e)?, ls.clone()), Assert(e) => Assert(v.visit_subexpr(e)?), - Embed(a) => return v.visit_embed_squash(a), + Embed(a) => Embed(v.visit_embed(a)?), }) } } -/// Like ExprFVeryGenericVisitor, but sets the return -/// type to ExprF<_> -pub trait ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>: Sized { - type Error; - - fn visit_subexpr(&mut self, subexpr: &'a SE1) -> Result<SE2, Self::Error>; - fn visit_embed(self, embed: &'a E1) -> Result<E2, Self::Error>; - - fn visit_subexpr_under_binder( - mut self, - _label: &'a Label, - subexpr: &'a SE1, - ) -> Result<SE2, Self::Error> { - self.visit_subexpr(subexpr) - } - - fn visit_embed_squash( - self, - embed: &'a E1, - ) -> Result<ExprF<SE2, E2>, Self::Error> { - Ok(ExprF::Embed(self.visit_embed(embed)?)) - } -} - -impl<'a, T, SE1, SE2, E1, E2> - ExprFVeryGenericVisitor<'a, ExprF<SE2, E2>, SE1, E1> for T +impl<'a, T, SE1, SE2, E1, E2> GenericVisitor<&'a ExprF<SE1, E1>, ExprF<SE2, E2>> + for T where - T: ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>, + T: ExprFInFallibleVisitor<'a, SE1, SE2, E1, E2>, { - type Error = T::Error; - type SE2 = SE2; - type E2 = E2; - - fn visit_subexpr( - &mut self, - subexpr: &'a SE1, - ) -> Result<Self::SE2, Self::Error> { - self.visit_subexpr(subexpr) - } - - fn visit_subexpr_under_binder( - self, - label: &'a Label, - subexpr: &'a SE1, - ) -> Result<Self::SE2, Self::Error> { - self.visit_subexpr_under_binder(label, subexpr) - } - - fn visit_embed_squash( - self, - embed: &'a E1, - ) -> Result<ExprF<SE2, E2>, Self::Error> { - self.visit_embed_squash(embed) - } - - // Called with the result of the map, in the non-embed case. - // Useful to change the result type, and/or avoid some loss of info - fn visit_resulting_exprf( - result: ExprF<Self::SE2, Self::E2>, - ) -> Result<ExprF<SE2, E2>, Self::Error> { - Ok(result) - } -} - -/// Like ExprFFallibleVisitor, but without the error handling. -pub trait ExprFInFallibleVisitor<'a, SE1, SE2, E1, E2>: Sized { - fn visit_subexpr(&mut self, subexpr: &'a SE1) -> SE2; - fn visit_embed(self, embed: &'a E1) -> E2; - - fn visit_subexpr_under_binder( - mut self, - _label: &'a Label, - subexpr: &'a SE1, - ) -> SE2 { - self.visit_subexpr(subexpr) - } - - fn visit_embed_squash(self, embed: &'a E1) -> ExprF<SE2, E2> { - ExprF::Embed(self.visit_embed(embed)) + fn visit(self, input: &'a ExprF<SE1, E1>) -> ExprF<SE2, E2> { + trivial_result(InfallibleWrapper(self).visit(input)) } } @@ -259,23 +191,6 @@ where ) -> Result<SE2, Self::Error> { Ok(self.0.visit_subexpr_under_binder(label, subexpr)) } - - fn visit_embed_squash( - self, - embed: &'a E1, - ) -> Result<ExprF<SE2, E2>, Self::Error> { - Ok(self.0.visit_embed_squash(embed)) - } -} - -impl<'a, T, SE1, SE2, E1, E2> GenericVisitor<&'a ExprF<SE1, E1>, ExprF<SE2, E2>> - for T -where - T: ExprFInFallibleVisitor<'a, SE1, SE2, E1, E2>, -{ - fn visit(self, input: &'a ExprF<SE1, E1>) -> ExprF<SE2, E2> { - trivial_result(InfallibleWrapper(self).visit(input)) - } } pub struct TraverseRefWithBindersVisitor<F1, F2> { |