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#![allow(non_snake_case)]
use dhall_core::core::*;
use dhall_generator::dhall_expr;
use std::fmt;
/// 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,
{
use dhall_core::BinOp::*;
use dhall_core::Builtin::*;
use dhall_core::Expr::*;
match e {
// Matches that don't normalize everything right away
Let(f, _, r, b) => {
let r2 = shift::<_, S, _>(1, &V(f.clone(), 0), r);
let b2 = subst::<_, S, _>(&V(f.clone(), 0), &r2, b);
let b3 = shift::<_, T, _>(-1, &V(f.clone(), 0), &b2);
normalize(&b3)
}
BoolIf(b, t, f) => match normalize(b) {
BoolLit(true) => normalize(t),
BoolLit(false) => normalize(f),
b2 => BoolIf(bx(b2), bx(normalize(t)), bx(normalize(f))),
},
Annot(x, _) => normalize(x),
Note(_, e) => normalize(e),
App(f, a) => match normalize::<S, T, A>(f) {
Lam(x, _A, b) => {
// Beta reduce
let vx0 = &V(x, 0);
let a2 = shift::<S, S, A>(1, vx0, a);
let b2 = subst::<S, T, A>(vx0, &a2, &b);
let b3 = shift::<S, T, A>(-1, vx0, &b2);
normalize(&b3)
}
f2 => match (f2, normalize::<S, T, A>(a)) {
// fold/build fusion for `List`
(App(box Builtin(ListBuild), _), App(box App(box Builtin(ListFold), _), box e2)) |
(App(box Builtin(ListFold), _), App(box App(box Builtin(ListBuild), _), box e2)) |
// fold/build fusion for `Optional`
(App(box Builtin(OptionalBuild), _), App(box App(box Builtin(OptionalFold), _), box e2)) |
(App(box Builtin(OptionalFold), _), App(box App(box Builtin(OptionalBuild), _), box e2)) |
// fold/build fusion for `Natural`
(Builtin(NaturalBuild), App(box Builtin(NaturalFold), box e2)) |
(Builtin(NaturalFold), App(box Builtin(NaturalBuild), box e2)) => normalize(&e2),
/*
App (App (App (App NaturalFold (NaturalLit n0)) _) succ') zero ->
normalize (go n0)
where
go !0 = zero
go !n = App succ' (go (n - 1))
App NaturalBuild k
| check -> NaturalLit n
| otherwise -> App f' a'
where
labeled =
normalize (App (App (App k Natural) "Succ") "Zero")
n = go 0 labeled
where
go !m (App (Var "Succ") e') = go (m + 1) e'
go !m (Var "Zero") = m
go !_ _ = internalError text
check = go labeled
where
go (App (Var "Succ") e') = go e'
go (Var "Zero") = True
go _ = False
*/
(Builtin(NaturalIsZero), NaturalLit(n)) => BoolLit(n == 0),
(Builtin(NaturalEven), NaturalLit(n)) => BoolLit(n % 2 == 0),
(Builtin(NaturalOdd), NaturalLit(n)) => BoolLit(n % 2 != 0),
(Builtin(NaturalToInteger), NaturalLit(n)) => IntegerLit(n as isize),
(Builtin(NaturalShow), NaturalLit(n)) => TextLit(n.to_string()),
(App(box Builtin(ListBuild), a0), k) => {
let k = bx(k);
let a1 = bx(shift(1, &V("a".into(), 0), &a0));
normalize(&dhall_expr!(k (List a0) (λ(a : a0) -> λ(as : List a1) -> [ a ] # as) ([] : List a0)))
}
(App(box App(box App(box App(box Builtin(ListFold), _), box ListLit(_, xs)), _), cons), nil) => {
let e2: Expr<_, _> = xs.into_iter().rev().fold(nil, |y, ys| {
let y = bx(y);
let ys = bx(ys);
dhall_expr!(cons y ys)
});
normalize(&e2)
}
(App(f, x_), ListLit(t, ys)) => match *f {
Builtin(ListLength) =>
NaturalLit(ys.len()),
Builtin(ListHead) =>
normalize(&OptionalLit(t, ys.into_iter().take(1).collect())),
Builtin(ListLast) =>
normalize(&OptionalLit(t, ys.into_iter().last().into_iter().collect())),
Builtin(ListReverse) => {
let mut xs = ys;
xs.reverse();
normalize(&ListLit(t, xs))
}
_ => app(App(f, x_), ListLit(t, ys)),
},
/*
App (App ListIndexed _) (ListLit t xs) ->
normalize (ListLit t' (fmap adapt (Data.Vector.indexed xs)))
where
t' = Record (Data.Map.fromList kts)
where
kts = [ ("index", Natural)
, ("value", t)
]
adapt (n, x) = RecordLit (Data.Map.fromList kvs)
where
kvs = [ ("index", NaturalLit (fromIntegral n))
, ("value", x)
]
*/
(App(box App(box App(box App(box Builtin(OptionalFold), _), box OptionalLit(_, xs)), _), just), nothing) => {
let e2: Expr<_, _> = xs.into_iter().fold(nothing, |y, _| {
let y = bx(y);
dhall_expr!(just y)
});
normalize(&e2)
}
(App(box Builtin(OptionalBuild), a0), g) => {
let g = bx(g);
normalize(&dhall_expr!((g (Optional a0)) (λ(x: a0) -> [x] : Optional a0) ([] : Optional a0)))
}
(f2, a2) => app(f2, a2),
},
},
// Normalize everything else before matching
e => {
match e.map_shallow(
normalize,
|_| unreachable!(),
|x| x.clone(),
|x| x.clone(),
) {
BinOp(BoolAnd, box BoolLit(x), box BoolLit(y)) => {
BoolLit(x && y)
}
BinOp(BoolOr, box BoolLit(x), box BoolLit(y)) => {
BoolLit(x || y)
}
BinOp(BoolEQ, box BoolLit(x), box BoolLit(y)) => {
BoolLit(x == y)
}
BinOp(BoolNE, box BoolLit(x), box BoolLit(y)) => {
BoolLit(x != y)
}
BinOp(NaturalPlus, box NaturalLit(x), box NaturalLit(y)) => {
NaturalLit(x + y)
}
BinOp(NaturalTimes, box NaturalLit(x), box NaturalLit(y)) => {
NaturalLit(x * y)
}
BinOp(TextAppend, box TextLit(x), box TextLit(y)) => {
TextLit(x + &y)
}
BinOp(ListAppend, box ListLit(t1, xs), box 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())
}
// Merge(_x, _y, _t) => unimplemented!(),
Field(box RecordLit(kvs), x) => match kvs.get(&x) {
Some(r) => r.clone(),
None => Field(bx(RecordLit(kvs)), x),
},
e => e,
}
}
}
}
|
