From 881248d2c4f0b4556a23d671d355bb7258adf8bb Mon Sep 17 00:00:00 2001 From: Nadrieril Date: Tue, 17 Dec 2019 14:33:06 +0000 Subject: Rename syntax::core to syntax::ast --- dhall/src/syntax/ast/visitor.rs | 360 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 360 insertions(+) create mode 100644 dhall/src/syntax/ast/visitor.rs (limited to 'dhall/src/syntax/ast/visitor.rs') diff --git a/dhall/src/syntax/ast/visitor.rs b/dhall/src/syntax/ast/visitor.rs new file mode 100644 index 0000000..b76d037 --- /dev/null +++ b/dhall/src/syntax/ast/visitor.rs @@ -0,0 +1,360 @@ +use crate::syntax::*; +use std::iter::FromIterator; + +/// 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 ExprFVisitor<'a, SE1, SE2, E1, E2>: Sized { + type Error; + + fn visit_subexpr(&mut self, subexpr: &'a SE1) -> Result; + fn visit_embed(self, embed: &'a E1) -> Result; + + fn visit_subexpr_under_binder( + mut self, + _label: &'a Label, + subexpr: &'a SE1, + ) -> Result { + self.visit_subexpr(subexpr) + } + + fn visit( + self, + input: &'a ExprF, + ) -> Result, Self::Error> { + visit_ref(self, input) + } +} + +/// Like `ExprFVisitor`, but by mutable reference +pub trait ExprFMutVisitor<'a, SE, E>: Sized { + type Error; + + fn visit_subexpr(&mut self, subexpr: &'a mut SE) + -> Result<(), Self::Error>; + fn visit_embed(self, _embed: &'a mut E) -> Result<(), Self::Error> { + Ok(()) + } + + fn visit_subexpr_under_binder( + mut self, + _label: &'a mut Label, + subexpr: &'a mut SE, + ) -> Result<(), Self::Error> { + self.visit_subexpr(subexpr) + } + + fn visit(self, input: &'a mut ExprF) -> Result<(), Self::Error> { + visit_mut(self, input) + } +} + +fn visit_ref<'a, V, SE1, SE2, E1, E2>( + mut v: V, + input: &'a ExprF, +) -> Result, V::Error> +where + V: ExprFVisitor<'a, SE1, SE2, E1, E2>, +{ + fn vec<'a, T, U, Err, F: FnMut(&'a T) -> Result>( + x: &'a [T], + f: F, + ) -> Result, Err> { + x.iter().map(f).collect() + } + fn opt<'a, T, U, Err, F: FnOnce(&'a T) -> Result>( + x: &'a Option, + f: F, + ) -> Result, Err> { + Ok(match x { + Some(x) => Some(f(x)?), + None => None, + }) + } + fn dupmap<'a, V, SE1, SE2, E1, E2, T>( + x: impl IntoIterator, + mut v: V, + ) -> Result + where + SE1: 'a, + T: FromIterator<(Label, SE2)>, + V: ExprFVisitor<'a, SE1, SE2, E1, E2>, + { + x.into_iter() + .map(|(k, x)| Ok((k.clone(), v.visit_subexpr(x)?))) + .collect() + } + fn optdupmap<'a, V, SE1, SE2, E1, E2, T>( + x: impl IntoIterator)>, + mut v: V, + ) -> Result + where + SE1: 'a, + T: FromIterator<(Label, Option)>, + V: ExprFVisitor<'a, SE1, SE2, E1, E2>, + { + x.into_iter() + .map(|(k, x)| { + Ok(( + k.clone(), + match x { + Some(x) => Some(v.visit_subexpr(x)?), + None => None, + }, + )) + }) + .collect() + } + + use crate::syntax::ExprF::*; + Ok(match input { + Var(v) => Var(v.clone()), + Lam(l, t, e) => { + let t = v.visit_subexpr(t)?; + let e = v.visit_subexpr_under_binder(l, e)?; + Lam(l.clone(), t, e) + } + Pi(l, t, e) => { + let t = v.visit_subexpr(t)?; + let e = v.visit_subexpr_under_binder(l, e)?; + Pi(l.clone(), t, e) + } + Let(l, t, a, e) => { + let t = opt(t, &mut |e| v.visit_subexpr(e))?; + let a = v.visit_subexpr(a)?; + let e = v.visit_subexpr_under_binder(l, e)?; + Let(l.clone(), t, a, e) + } + App(f, a) => App(v.visit_subexpr(f)?, v.visit_subexpr(a)?), + Annot(x, t) => Annot(v.visit_subexpr(x)?, v.visit_subexpr(t)?), + Const(k) => Const(*k), + Builtin(v) => Builtin(*v), + BoolLit(b) => BoolLit(*b), + NaturalLit(n) => NaturalLit(*n), + IntegerLit(n) => IntegerLit(*n), + DoubleLit(n) => DoubleLit(*n), + TextLit(t) => TextLit(t.traverse_ref(|e| v.visit_subexpr(e))?), + BinOp(o, x, y) => BinOp(*o, v.visit_subexpr(x)?, v.visit_subexpr(y)?), + BoolIf(b, t, f) => BoolIf( + v.visit_subexpr(b)?, + v.visit_subexpr(t)?, + v.visit_subexpr(f)?, + ), + EmptyListLit(t) => EmptyListLit(v.visit_subexpr(t)?), + NEListLit(es) => NEListLit(vec(es, |e| v.visit_subexpr(e))?), + SomeLit(e) => SomeLit(v.visit_subexpr(e)?), + RecordType(kts) => RecordType(dupmap(kts, v)?), + RecordLit(kvs) => RecordLit(dupmap(kvs, v)?), + UnionType(kts) => UnionType(optdupmap(kts, v)?), + Merge(x, y, t) => Merge( + v.visit_subexpr(x)?, + v.visit_subexpr(y)?, + opt(t, |e| v.visit_subexpr(e))?, + ), + ToMap(x, t) => { + ToMap(v.visit_subexpr(x)?, opt(t, |e| v.visit_subexpr(e))?) + } + Field(e, l) => Field(v.visit_subexpr(e)?, l.clone()), + Projection(e, ls) => Projection(v.visit_subexpr(e)?, ls.clone()), + ProjectionByExpr(e, x) => { + ProjectionByExpr(v.visit_subexpr(e)?, v.visit_subexpr(x)?) + } + Assert(e) => Assert(v.visit_subexpr(e)?), + Import(i) => Import(i.traverse_ref(|e| v.visit_subexpr(e))?), + Embed(a) => Embed(v.visit_embed(a)?), + }) +} + +fn visit_mut<'a, V, SE, E>( + mut v: V, + input: &'a mut ExprF, +) -> Result<(), V::Error> +where + V: ExprFMutVisitor<'a, SE, E>, +{ + fn vec<'a, V, SE, E>(v: &mut V, x: &'a mut Vec) -> Result<(), V::Error> + where + V: ExprFMutVisitor<'a, SE, E>, + { + for x in x { + v.visit_subexpr(x)?; + } + Ok(()) + } + fn opt<'a, V, SE, E>( + v: &mut V, + x: &'a mut Option, + ) -> Result<(), V::Error> + where + V: ExprFMutVisitor<'a, SE, E>, + { + if let Some(x) = x { + v.visit_subexpr(x)?; + } + Ok(()) + } + fn dupmap<'a, V, SE, E>( + mut v: V, + x: impl IntoIterator, + ) -> Result<(), V::Error> + where + SE: 'a, + V: ExprFMutVisitor<'a, SE, E>, + { + for (_, x) in x { + v.visit_subexpr(x)?; + } + Ok(()) + } + fn optdupmap<'a, V, SE, E>( + mut v: V, + x: impl IntoIterator)>, + ) -> Result<(), V::Error> + where + SE: 'a, + V: ExprFMutVisitor<'a, SE, E>, + { + for (_, x) in x { + opt(&mut v, x)?; + } + Ok(()) + } + + use crate::syntax::ExprF::*; + match input { + Var(_) | Const(_) | Builtin(_) | BoolLit(_) | NaturalLit(_) + | IntegerLit(_) | DoubleLit(_) => {} + Lam(l, t, e) => { + v.visit_subexpr(t)?; + v.visit_subexpr_under_binder(l, e)?; + } + Pi(l, t, e) => { + v.visit_subexpr(t)?; + v.visit_subexpr_under_binder(l, e)?; + } + Let(l, t, a, e) => { + opt(&mut v, t)?; + v.visit_subexpr(a)?; + v.visit_subexpr_under_binder(l, e)?; + } + App(f, a) => { + v.visit_subexpr(f)?; + v.visit_subexpr(a)?; + } + Annot(x, t) => { + v.visit_subexpr(x)?; + v.visit_subexpr(t)?; + } + TextLit(t) => t.traverse_mut(|e| v.visit_subexpr(e))?, + BinOp(_, x, y) => { + v.visit_subexpr(x)?; + v.visit_subexpr(y)?; + } + BoolIf(b, t, f) => { + v.visit_subexpr(b)?; + v.visit_subexpr(t)?; + v.visit_subexpr(f)?; + } + EmptyListLit(t) => v.visit_subexpr(t)?, + NEListLit(es) => vec(&mut v, es)?, + SomeLit(e) => v.visit_subexpr(e)?, + RecordType(kts) => dupmap(v, kts)?, + RecordLit(kvs) => dupmap(v, kvs)?, + UnionType(kts) => optdupmap(v, kts)?, + Merge(x, y, t) => { + v.visit_subexpr(x)?; + v.visit_subexpr(y)?; + opt(&mut v, t)?; + } + ToMap(x, t) => { + v.visit_subexpr(x)?; + opt(&mut v, t)?; + } + Field(e, _) => v.visit_subexpr(e)?, + Projection(e, _) => v.visit_subexpr(e)?, + ProjectionByExpr(e, x) => { + v.visit_subexpr(e)?; + v.visit_subexpr(x)?; + } + Assert(e) => v.visit_subexpr(e)?, + Import(i) => i.traverse_mut(|e| v.visit_subexpr(e))?, + Embed(a) => v.visit_embed(a)?, + } + Ok(()) +} + +pub struct TraverseRefWithBindersVisitor { + pub visit_subexpr: F1, + pub visit_under_binder: F2, +} + +impl<'a, SE, E, SE2, Err, F1, F2> ExprFVisitor<'a, SE, SE2, E, E> + for TraverseRefWithBindersVisitor +where + SE: 'a, + E: 'a + Clone, + F1: FnMut(&'a SE) -> Result, + F2: FnOnce(&'a Label, &'a SE) -> Result, +{ + type Error = Err; + + fn visit_subexpr(&mut self, subexpr: &'a SE) -> Result { + (self.visit_subexpr)(subexpr) + } + fn visit_subexpr_under_binder( + self, + label: &'a Label, + subexpr: &'a SE, + ) -> Result { + (self.visit_under_binder)(label, subexpr) + } + fn visit_embed(self, embed: &'a E) -> Result { + Ok(embed.clone()) + } +} + +pub struct TraverseRefVisitor { + pub visit_subexpr: F1, +} + +impl<'a, SE, E, SE2, Err, F1> ExprFVisitor<'a, SE, SE2, E, E> + for TraverseRefVisitor +where + SE: 'a, + E: 'a + Clone, + F1: FnMut(&'a SE) -> Result, +{ + type Error = Err; + + fn visit_subexpr(&mut self, subexpr: &'a SE) -> Result { + (self.visit_subexpr)(subexpr) + } + fn visit_embed(self, embed: &'a E) -> Result { + Ok(embed.clone()) + } +} + +pub struct TraverseMutVisitor { + pub visit_subexpr: F1, +} + +impl<'a, SE, E, Err, F1> ExprFMutVisitor<'a, SE, E> for TraverseMutVisitor +where + SE: 'a, + E: 'a, + F1: FnMut(&'a mut SE) -> Result<(), Err>, +{ + type Error = Err; + + fn visit_subexpr( + &mut self, + subexpr: &'a mut SE, + ) -> Result<(), Self::Error> { + (self.visit_subexpr)(subexpr) + } +} -- cgit v1.2.3