Merge dhall_normalize back into dhall; that was unnecessary

1 files changed, 181 insertions, 0 deletions

diff --git a/dhall/src/normalize.rs b/dhall/src/normalize.rs
new file mode 100644
index 0000000..ec594da
--- /dev/null
+++ b/dhall/src/normalize.rs
@@ -0,0 +1,181 @@
+#![allow(non_snake_case)]
+use dhall_core::core::*;
+use dhall_generator::dhall;
+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<'i, S, T, A>(e: &Expr<'i, S, A>) -> Expr<'i, 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, 0), r);
+            let b2 = subst(V(f, 0), &r2, b);
+            let b3 = shift::<_, T, _>(-1, V(f, 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", 0), &a0));
+                    normalize(&dhall!(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!(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!(just y)
+                    });
+                    normalize(&e2)
+                }
+                (App(box Builtin(OptionalBuild), a0), g) => {
+                    let g = bx(g);
+                    normalize(&dhall!((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!()) {
+            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.len() == 0 && ys.len() == 0 {
+                    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,
+        },
+    }
+}