Merge pull request #159 from Nadrieril/operations

Factor out operations

1 files changed, 306 insertions, 0 deletions

diff --git a/dhall/src/operations/normalization.rs b/dhall/src/operations/normalization.rs
new file mode 100644
index 0000000..e3a9415
--- /dev/null
+++ b/dhall/src/operations/normalization.rs
@@ -0,0 +1,306 @@
+use itertools::Itertools;
+use std::collections::HashMap;
+use std::iter::once;
+
+use crate::operations::{BinOp, OpKind};
+use crate::semantics::{
+    merge_maps, ret_kind, ret_op, ret_ref, Nir, NirKind, Ret, TextLit,
+};
+use crate::syntax::{ExprKind, Label, NumKind};
+
+fn normalize_binop(o: BinOp, x: &Nir, y: &Nir) -> Ret {
+    use BinOp::*;
+    use NirKind::{EmptyListLit, NEListLit, Num, RecordLit, RecordType};
+    use NumKind::{Bool, Natural};
+
+    match (o, x.kind(), y.kind()) {
+        (BoolAnd, Num(Bool(true)), _) => ret_ref(y),
+        (BoolAnd, _, Num(Bool(true))) => ret_ref(x),
+        (BoolAnd, Num(Bool(false)), _) => ret_kind(Num(Bool(false))),
+        (BoolAnd, _, Num(Bool(false))) => ret_kind(Num(Bool(false))),
+        (BoolAnd, _, _) if x == y => ret_ref(x),
+        (BoolOr, Num(Bool(true)), _) => ret_kind(Num(Bool(true))),
+        (BoolOr, _, Num(Bool(true))) => ret_kind(Num(Bool(true))),
+        (BoolOr, Num(Bool(false)), _) => ret_ref(y),
+        (BoolOr, _, Num(Bool(false))) => ret_ref(x),
+        (BoolOr, _, _) if x == y => ret_ref(x),
+        (BoolEQ, Num(Bool(true)), _) => ret_ref(y),
+        (BoolEQ, _, Num(Bool(true))) => ret_ref(x),
+        (BoolEQ, Num(Bool(x)), Num(Bool(y))) => ret_kind(Num(Bool(x == y))),
+        (BoolEQ, _, _) if x == y => ret_kind(Num(Bool(true))),
+        (BoolNE, Num(Bool(false)), _) => ret_ref(y),
+        (BoolNE, _, Num(Bool(false))) => ret_ref(x),
+        (BoolNE, Num(Bool(x)), Num(Bool(y))) => ret_kind(Num(Bool(x != y))),
+        (BoolNE, _, _) if x == y => ret_kind(Num(Bool(false))),
+
+        (NaturalPlus, Num(Natural(0)), _) => ret_ref(y),
+        (NaturalPlus, _, Num(Natural(0))) => ret_ref(x),
+        (NaturalPlus, Num(Natural(x)), Num(Natural(y))) => {
+            ret_kind(Num(Natural(x + y)))
+        }
+        (NaturalTimes, Num(Natural(0)), _) => ret_kind(Num(Natural(0))),
+        (NaturalTimes, _, Num(Natural(0))) => ret_kind(Num(Natural(0))),
+        (NaturalTimes, Num(Natural(1)), _) => ret_ref(y),
+        (NaturalTimes, _, Num(Natural(1))) => ret_ref(x),
+        (NaturalTimes, Num(Natural(x)), Num(Natural(y))) => {
+            ret_kind(Num(Natural(x * y)))
+        }
+
+        (ListAppend, EmptyListLit(_), _) => ret_ref(y),
+        (ListAppend, _, EmptyListLit(_)) => ret_ref(x),
+        (ListAppend, NEListLit(xs), NEListLit(ys)) => {
+            ret_kind(NEListLit(xs.iter().chain(ys.iter()).cloned().collect()))
+        }
+
+        (TextAppend, NirKind::TextLit(x), _) if x.is_empty() => ret_ref(y),
+        (TextAppend, _, NirKind::TextLit(y)) if y.is_empty() => ret_ref(x),
+        (TextAppend, NirKind::TextLit(x), NirKind::TextLit(y)) => {
+            ret_kind(NirKind::TextLit(x.concat(y)))
+        }
+        (TextAppend, NirKind::TextLit(x), _) => ret_kind(NirKind::TextLit(
+            x.concat(&TextLit::interpolate(y.clone())),
+        )),
+        (TextAppend, _, NirKind::TextLit(y)) => ret_kind(NirKind::TextLit(
+            TextLit::interpolate(x.clone()).concat(y),
+        )),
+
+        (RightBiasedRecordMerge, _, RecordLit(kvs)) if kvs.is_empty() => {
+            ret_ref(x)
+        }
+        (RightBiasedRecordMerge, RecordLit(kvs), _) if kvs.is_empty() => {
+            ret_ref(y)
+        }
+        (RightBiasedRecordMerge, RecordLit(kvs1), RecordLit(kvs2)) => {
+            let mut kvs = kvs2.clone();
+            for (x, v) in kvs1 {
+                // Insert only if key not already present
+                kvs.entry(x.clone()).or_insert_with(|| v.clone());
+            }
+            ret_kind(RecordLit(kvs))
+        }
+        (RightBiasedRecordMerge, _, _) if x == y => ret_ref(y),
+
+        (RecursiveRecordMerge, _, RecordLit(kvs)) if kvs.is_empty() => {
+            ret_ref(x)
+        }
+        (RecursiveRecordMerge, RecordLit(kvs), _) if kvs.is_empty() => {
+            ret_ref(y)
+        }
+        (RecursiveRecordMerge, RecordLit(kvs1), RecordLit(kvs2)) => {
+            let kvs = merge_maps(kvs1, kvs2, |_, v1, v2| {
+                Nir::from_partial_expr(ExprKind::Op(OpKind::BinOp(
+                    RecursiveRecordMerge,
+                    v1.clone(),
+                    v2.clone(),
+                )))
+            });
+            ret_kind(RecordLit(kvs))
+        }
+
+        (RecursiveRecordTypeMerge, RecordType(kts_x), RecordType(kts_y)) => {
+            let kts = merge_maps(
+                kts_x,
+                kts_y,
+                // If the Label exists for both records, then we hit the recursive case.
+                |_, l: &Nir, r: &Nir| {
+                    Nir::from_partial_expr(ExprKind::Op(OpKind::BinOp(
+                        RecursiveRecordTypeMerge,
+                        l.clone(),
+                        r.clone(),
+                    )))
+                },
+            );
+            ret_kind(RecordType(kts))
+        }
+
+        (Equivalence, _, _) => {
+            ret_kind(NirKind::Equivalence(x.clone(), y.clone()))
+        }
+
+        _ => ret_op(OpKind::BinOp(o, x.clone(), y.clone())),
+    }
+}
+
+fn normalize_field(v: &Nir, field: &Label) -> Ret {
+    use self::BinOp::{RecursiveRecordMerge, RightBiasedRecordMerge};
+    use NirKind::{Op, RecordLit, UnionConstructor, UnionType};
+    use OpKind::{BinOp, Field, Projection};
+    let nothing_to_do = || ret_op(Field(v.clone(), field.clone()));
+
+    match v.kind() {
+        RecordLit(kvs) => match kvs.get(field) {
+            Some(r) => ret_ref(r),
+            None => nothing_to_do(),
+        },
+        UnionType(kts) => {
+            ret_kind(UnionConstructor(field.clone(), kts.clone()))
+        }
+        Op(Projection(x, _)) => normalize_field(x, field),
+        Op(BinOp(RightBiasedRecordMerge, x, y)) => match (x.kind(), y.kind()) {
+            (_, RecordLit(kvs)) => match kvs.get(field) {
+                Some(r) => ret_ref(r),
+                None => normalize_field(x, field),
+            },
+            (RecordLit(kvs), _) => match kvs.get(field) {
+                Some(r) => ret_op(Field(
+                    Nir::from_kind(Op(BinOp(
+                        RightBiasedRecordMerge,
+                        Nir::from_kind(RecordLit(
+                            once((field.clone(), r.clone())).collect(),
+                        )),
+                        y.clone(),
+                    ))),
+                    field.clone(),
+                )),
+                None => normalize_field(y, field),
+            },
+            _ => nothing_to_do(),
+        },
+        Op(BinOp(RecursiveRecordMerge, x, y)) => match (x.kind(), y.kind()) {
+            (RecordLit(kvs), _) => match kvs.get(field) {
+                Some(r) => ret_op(Field(
+                    Nir::from_kind(Op(BinOp(
+                        RecursiveRecordMerge,
+                        Nir::from_kind(RecordLit(
+                            once((field.clone(), r.clone())).collect(),
+                        )),
+                        y.clone(),
+                    ))),
+                    field.clone(),
+                )),
+                None => normalize_field(y, field),
+            },
+            (_, RecordLit(kvs)) => match kvs.get(field) {
+                Some(r) => ret_op(Field(
+                    Nir::from_kind(Op(BinOp(
+                        RecursiveRecordMerge,
+                        x.clone(),
+                        Nir::from_kind(RecordLit(
+                            once((field.clone(), r.clone())).collect(),
+                        )),
+                    ))),
+                    field.clone(),
+                )),
+                None => normalize_field(x, field),
+            },
+            _ => nothing_to_do(),
+        },
+        _ => nothing_to_do(),
+    }
+}
+
+pub fn normalize_operation(opkind: &OpKind<Nir>) -> Ret {
+    use self::BinOp::RightBiasedRecordMerge;
+    use NirKind::{
+        EmptyListLit, EmptyOptionalLit, NEListLit, NEOptionalLit, Num, Op,
+        RecordLit, RecordType, UnionConstructor, UnionLit,
+    };
+    use NumKind::Bool;
+    use OpKind::*;
+    let nothing_to_do = || ret_op(opkind.clone());
+
+    match opkind {
+        App(v, a) => ret_kind(v.app_to_kind(a.clone())),
+        BinOp(o, x, y) => normalize_binop(*o, x, y),
+        BoolIf(b, e1, e2) => {
+            match b.kind() {
+                Num(Bool(true)) => ret_ref(e1),
+                Num(Bool(false)) => ret_ref(e2),
+                _ => {
+                    match (e1.kind(), e2.kind()) {
+                        // Simplify `if b then True else False`
+                        (Num(Bool(true)), Num(Bool(false))) => ret_ref(b),
+                        _ if e1 == e2 => ret_ref(e1),
+                        _ => nothing_to_do(),
+                    }
+                }
+            }
+        }
+        Merge(handlers, variant, _) => match handlers.kind() {
+            RecordLit(kvs) => match variant.kind() {
+                UnionConstructor(l, _) => match kvs.get(l) {
+                    Some(h) => ret_ref(h),
+                    None => nothing_to_do(),
+                },
+                UnionLit(l, v, _) => match kvs.get(l) {
+                    Some(h) => ret_kind(h.app_to_kind(v.clone())),
+                    None => nothing_to_do(),
+                },
+                EmptyOptionalLit(_) => match kvs.get(&"None".into()) {
+                    Some(h) => ret_ref(h),
+                    None => nothing_to_do(),
+                },
+                NEOptionalLit(v) => match kvs.get(&"Some".into()) {
+                    Some(h) => ret_kind(h.app_to_kind(v.clone())),
+                    None => nothing_to_do(),
+                },
+                _ => nothing_to_do(),
+            },
+            _ => nothing_to_do(),
+        },
+        ToMap(v, annot) => match v.kind() {
+            RecordLit(kvs) if kvs.is_empty() => {
+                match annot.as_ref().map(|v| v.kind()) {
+                    Some(NirKind::ListType(t)) => {
+                        ret_kind(EmptyListLit(t.clone()))
+                    }
+                    _ => nothing_to_do(),
+                }
+            }
+            RecordLit(kvs) => ret_kind(NEListLit(
+                kvs.iter()
+                    .sorted_by_key(|(k, _)| *k)
+                    .map(|(k, v)| {
+                        let mut rec = HashMap::new();
+                        rec.insert("mapKey".into(), Nir::from_text(k));
+                        rec.insert("mapValue".into(), v.clone());
+                        Nir::from_kind(NirKind::RecordLit(rec))
+                    })
+                    .collect(),
+            )),
+            _ => nothing_to_do(),
+        },
+        Field(v, field) => normalize_field(v, field),
+        Projection(_, ls) if ls.is_empty() => {
+            ret_kind(RecordLit(HashMap::new()))
+        }
+        Projection(v, ls) => match v.kind() {
+            RecordLit(kvs) => ret_kind(RecordLit(
+                ls.iter()
+                    .filter_map(|l| kvs.get(l).map(|x| (l.clone(), x.clone())))
+                    .collect(),
+            )),
+            Op(Projection(v2, _)) => {
+                normalize_operation(&Projection(v2.clone(), ls.clone()))
+            }
+            Op(BinOp(RightBiasedRecordMerge, l, r)) => match r.kind() {
+                RecordLit(kvs) => {
+                    let r_keys = kvs.keys().cloned().collect();
+                    normalize_operation(&BinOp(
+                        RightBiasedRecordMerge,
+                        Nir::from_partial_expr(ExprKind::Op(Projection(
+                            l.clone(),
+                            ls.difference(&r_keys).cloned().collect(),
+                        ))),
+                        Nir::from_partial_expr(ExprKind::Op(Projection(
+                            r.clone(),
+                            ls.intersection(&r_keys).cloned().collect(),
+                        ))),
+                    ))
+                }
+                _ => nothing_to_do(),
+            },
+            _ => nothing_to_do(),
+        },
+        ProjectionByExpr(v, t) => match t.kind() {
+            RecordType(kts) => normalize_operation(&Projection(
+                v.clone(),
+                kts.keys().cloned().collect(),
+            )),
+            _ => nothing_to_do(),
+        },
+        Completion(..) => {
+            unreachable!("This case should have been handled in resolution")
+        }
+    }
+}