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use std::iter::FromIterator;
use crate::syntax::*;
/// A visitor trait that can be used to traverse `ExprKind`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 ExprKindVisitor<'a, SE1, SE2>: Sized {
type Error;
fn visit_subexpr(&mut self, subexpr: &'a SE1) -> Result<SE2, 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(
self,
input: &'a ExprKind<SE1>,
) -> Result<ExprKind<SE2>, Self::Error> {
visit_ref(self, input)
}
}
fn visit_ref<'a, V, SE1, SE2>(
mut v: V,
input: &'a ExprKind<SE1>,
) -> Result<ExprKind<SE2>, V::Error>
where
V: ExprKindVisitor<'a, SE1, SE2>,
{
fn vec<'a, T, U, Err, F: FnMut(&'a T) -> Result<U, Err>>(
x: &'a [T],
f: F,
) -> Result<Vec<U>, Err> {
x.iter().map(f).collect()
}
fn opt<'a, T, U, Err, F: FnOnce(&'a T) -> Result<U, Err>>(
x: &'a Option<T>,
f: F,
) -> Result<Option<U>, Err> {
Ok(match x {
Some(x) => Some(f(x)?),
None => None,
})
}
fn dupmap<'a, V, SE1, SE2, T>(
x: impl IntoIterator<Item = (&'a Label, &'a SE1)>,
mut v: V,
) -> Result<T, V::Error>
where
SE1: 'a,
T: FromIterator<(Label, SE2)>,
V: ExprKindVisitor<'a, SE1, SE2>,
{
x.into_iter()
.map(|(k, x)| Ok((k.clone(), v.visit_subexpr(x)?)))
.collect()
}
fn optdupmap<'a, V, SE1, SE2, T>(
x: impl IntoIterator<Item = (&'a Label, &'a Option<SE1>)>,
mut v: V,
) -> Result<T, V::Error>
where
SE1: 'a,
T: FromIterator<(Label, Option<SE2>)>,
V: ExprKindVisitor<'a, SE1, SE2>,
{
x.into_iter()
.map(|(k, x)| {
Ok((
k.clone(),
match x {
Some(x) => Some(v.visit_subexpr(x)?),
None => None,
},
))
})
.collect()
}
use crate::syntax::ExprKind::*;
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)?)
}
Completion(e, x) => {
Completion(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))?),
})
}
pub struct TraverseRefMaybeBinderVisitor<F>(pub F);
impl<'a, SE, SE2, Err, F> ExprKindVisitor<'a, SE, SE2>
for TraverseRefMaybeBinderVisitor<F>
where
SE: 'a,
F: FnMut(Option<&'a Label>, &'a SE) -> Result<SE2, Err>,
{
type Error = Err;
fn visit_subexpr(&mut self, subexpr: &'a SE) -> Result<SE2, Self::Error> {
(self.0)(None, subexpr)
}
fn visit_subexpr_under_binder(
mut self,
label: &'a Label,
subexpr: &'a SE,
) -> Result<SE2, Self::Error> {
(self.0)(Some(label), subexpr)
}
}
|
