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#![allow(non_snake_case)]
use dhall_core::core::*;
use dhall_generator::dhall_expr;
use std::fmt;
use std::rc::Rc;
/// Reduce an expression to its weak head normal form, i.e. normalize
/// just enough to get the first constructor of the final expression
/// Is identical to normalize on primitive types, but not on more complex
/// types like functions and records.
/// This allows normalization to be lazy.
pub fn normalize_whnf<S, A>(e: &Expr<S, A>) -> Expr<S, A>
where
S: Clone + fmt::Debug,
A: Clone + fmt::Debug,
{
use dhall_core::BinOp::*;
use dhall_core::Builtin::*;
use dhall_core::Expr::*;
match e {
Let(f, _, r, b) => {
let vf0 = &V(f.clone(), 0);
let r2 = shift::<_, S, _>(1, vf0, r);
let b2 = subst::<_, S, _>(vf0, &r2, b);
let b3 = shift::<_, S, _>(-1, vf0, &b2);
normalize_whnf(&b3)
}
Annot(x, _) => normalize_whnf(x),
Note(_, e) => normalize_whnf(e),
App(f, args) => match (normalize_whnf(f), args.as_slice()) {
(f, []) => f,
(App(f, args1), args2) => normalize_whnf(&App(
f.clone(),
args1.iter().chain(args2.iter()).cloned().collect(),
)),
(Lam(ref x, _, ref b), [a, rest..]) => {
// Beta reduce
let vx0 = &V(x.clone(), 0);
let a2 = shift::<S, S, A>(1, vx0, a);
let b2 = subst::<S, S, A>(vx0, &a2, &b);
let b3 = shift::<S, S, A>(-1, vx0, &b2);
normalize_whnf(&App(bx(b3), rest.to_vec()))
}
// TODO: this is more normalization than needed
(Builtin(b), args) => match (
b,
args.iter()
.map(|x| normalize_whnf(&*x))
.collect::<Vec<Expr<_, _>>>()
.as_slice(),
) {
(OptionalSome, [a]) => OptionalLit(None, Some(bx(a.clone()))),
(OptionalNone, [a]) => OptionalLit(Some(bx(a.clone())), None),
(NaturalIsZero, [NaturalLit(n)]) => BoolLit(*n == 0),
(NaturalEven, [NaturalLit(n)]) => BoolLit(*n % 2 == 0),
(NaturalOdd, [NaturalLit(n)]) => BoolLit(*n % 2 != 0),
(NaturalToInteger, [NaturalLit(n)]) => IntegerLit(*n as isize),
(NaturalShow, [NaturalLit(n)]) => TextLit(n.to_string().into()),
(ListLength, [_, ListLit(_, ys)]) => NaturalLit(ys.len()),
(ListHead, [_, ListLit(t, ys)]) => {
OptionalLit(t.clone(), ys.iter().cloned().next())
}
(ListLast, [_, ListLit(t, ys)]) => {
OptionalLit(t.clone(), ys.iter().cloned().last())
}
(ListReverse, [_, ListLit(t, ys)]) => {
let xs = ys.iter().rev().cloned().collect();
ListLit(t.clone(), xs)
}
(ListBuild, [a0, g]) => {
// fold/build fusion
let g = match g {
App(f, args) => match (&**f, args.as_slice()) {
(Builtin(ListFold), [_, x, rest..]) => {
return normalize_whnf(&App(
x.clone(),
rest.to_vec(),
))
}
(_, args) => App(f.clone(), args.to_vec()),
},
g => g.clone(),
};
let g = bx(g);
let a0 = bx(a0.clone());
let a1 = bx(shift(1, &V("a".into(), 0), &a0));
normalize_whnf(
&dhall_expr!(g (List a0) (λ(a : a0) -> λ(as : List a1) -> [ a ] # as) ([] : List a0)),
)
}
(OptionalBuild, [a0, g]) => {
// fold/build fusion
let g = match g {
App(f, args) => match (&**f, args.as_slice()) {
(Builtin(OptionalFold), [_, x, rest..]) => {
return normalize_whnf(&App(
x.clone(),
rest.to_vec(),
))
}
(_, args) => App(f.clone(), args.to_vec()),
},
g => g.clone(),
};
let g = bx(g);
let a0 = bx(a0.clone());
normalize_whnf(
&dhall_expr!((g (Optional a0)) (λ(x: a0) -> [x] : Optional a0) ([] : Optional a0)),
)
}
(ListFold, [_, ListLit(_, xs), _, cons, nil]) => {
let e2: Expr<_, _> =
xs.iter().rev().fold((*nil).clone(), |acc, x| {
let x = (x).clone();
let acc = bx((acc).clone());
let cons = bx((cons).clone());
dhall_expr!(cons x acc)
});
normalize_whnf(&e2)
}
// // fold/build fusion
// (ListFold, [_, App(box Builtin(ListBuild), [_, x, rest..]), rest..]) => {
// normalize_whnf(&App(bx(x.clone()), rest.to_vec()))
// }
(OptionalFold, [_, OptionalLit(_, Some(x)), _, just, _]) => {
let x = x.clone();
let just = bx(just.clone());
normalize_whnf(&dhall_expr!(just x))
}
(OptionalFold, [_, OptionalLit(_, None), _, _, nothing]) => {
(*nothing).clone()
}
// // fold/build fusion
// (OptionalFold, [_, App(box Builtin(OptionalBuild), [_, x, rest..]), rest..]) => {
// normalize_whnf(&App(bx(x.clone()), rest.to_vec()))
// }
(NaturalBuild, [App(f, args)]) => {
match (&**f, args.as_slice()) {
// fold/build fusion
(Builtin(NaturalFold), [x, rest..]) => {
normalize_whnf(&App(x.clone(), rest.to_vec()))
}
(_, args) => app(
Builtin(NaturalBuild),
vec![bx(App(f.clone(), args.to_vec()))],
),
}
}
(NaturalFold, [App(f, args)]) => {
match (&**f, args.as_slice()) {
// fold/build fusion
(Builtin(NaturalBuild), [x, rest..]) => {
normalize_whnf(&App(x.clone(), rest.to_vec()))
}
(_, args) => app(
Builtin(NaturalFold),
vec![bx(App(f.clone(), args.to_vec()))],
),
}
}
(b, args) => {
App(bx(Builtin(b)), args.iter().cloned().map(bx).collect())
}
},
(f, args) => App(bx(f), args.to_vec()),
},
BoolIf(b, t, f) => match normalize_whnf(b) {
BoolLit(true) => normalize_whnf(t),
BoolLit(false) => normalize_whnf(f),
b2 => BoolIf(bx(b2), t.clone(), f.clone()),
},
OptionalLit(t, es) => {
if !es.is_none() {
OptionalLit(None, es.clone())
} else {
OptionalLit(t.clone(), es.clone())
}
}
BinOp(o, x, y) => match (o, normalize_whnf(&x), normalize_whnf(&y)) {
(BoolAnd, BoolLit(x), BoolLit(y)) => BoolLit(x && y),
(BoolOr, BoolLit(x), BoolLit(y)) => BoolLit(x || y),
(BoolEQ, BoolLit(x), BoolLit(y)) => BoolLit(x == y),
(BoolNE, BoolLit(x), BoolLit(y)) => BoolLit(x != y),
(NaturalPlus, NaturalLit(x), NaturalLit(y)) => NaturalLit(x + y),
(NaturalTimes, NaturalLit(x), NaturalLit(y)) => NaturalLit(x * y),
(TextAppend, TextLit(x), TextLit(y)) => TextLit(x + y),
(ListAppend, ListLit(t1, xs), ListLit(t2, ys)) => {
// Drop type annotation if the result is nonempty
let t = if xs.is_empty() && ys.is_empty() {
t1.or(t2)
} else {
None
};
let xs = xs.into_iter();
let ys = ys.into_iter();
ListLit(t, xs.chain(ys).collect())
}
(o, x, y) => BinOp(*o, bx(x), bx(y)),
},
Field(e, x) => match (normalize_whnf(&e), x) {
(RecordLit(kvs), x) => match kvs.get(&x) {
Some(r) => normalize_whnf(r),
None => Field(bx(RecordLit(kvs)), x.clone()),
},
(e, x) => Field(bx(e), x.clone()),
},
e => e.clone(),
}
}
/// Reduce an expression to its normal form, performing beta reduction
///
/// `normalize` does not type-check the expression. You may want to type-check
/// expressions before normalizing them since normalization can convert an
/// ill-typed expression into a well-typed expression.
///
/// However, `normalize` will not fail if the expression is ill-typed and will
/// leave ill-typed sub-expressions unevaluated.
///
pub fn normalize<S, T, A>(e: &Expr<S, A>) -> Expr<T, A>
where
S: Clone + fmt::Debug,
T: Clone + fmt::Debug,
A: Clone + fmt::Debug,
{
normalize_whnf(e).map_shallow(
normalize,
|_| unreachable!(),
|x| x.clone(),
|x| x.clone(),
)
}
|
