From 63d3356f40ef48a7735a2151a14ad9952fc245db Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Wed, 17 Apr 2019 01:22:28 +0200
Subject: Normalize union constructors

---
 dhall/src/normalize.rs    | 26 ++++++++++++++++++++++----
 dhall_core/src/core.rs    |  2 ++
 dhall_core/src/printer.rs | 14 ++++++++++++--
 dhall_core/src/visitor.rs |  7 +++++--
 4 files changed, 41 insertions(+), 8 deletions(-)

diff --git a/dhall/src/normalize.rs b/dhall/src/normalize.rs
index 2bbaf52..e0ed96c 100644
--- a/dhall/src/normalize.rs
+++ b/dhall/src/normalize.rs
@@ -234,6 +234,7 @@ fn normalize_ref(expr: &Expr<X, Normalized<'static>>) -> Expr<X, X> {
         expr.map_ref_simple(|e| normalize_ref(e.as_ref()));
 
     use WhatNext::*;
+    // TODO: match by move
     let what_next = match &expr {
         Let(f, _, r, b) => {
             let vf0 = &V(f.clone(), 0);
@@ -261,6 +262,13 @@ fn normalize_ref(expr: &Expr<X, Normalized<'static>>) -> Expr<X, X> {
             let b2 = subst_shift(vx0, &a.roll(), &b);
             Continue(App(b2, iter.map(ExprF::roll).collect()))
         }
+        App(UnionConstructor(l, kts), args) => {
+            let mut iter = args.iter();
+            // We know args is nonempty
+            let a = iter.next().unwrap();
+            let e = rc(UnionLit(l.clone(), rc(a.clone()), kts.clone()));
+            Continue(App(e, iter.map(ExprF::roll).collect()))
+        }
         BoolIf(BoolLit(true), t, _) => DoneRef(t),
         BoolIf(BoolLit(false), _, f) => DoneRef(f),
         // TODO: interpolation
@@ -285,16 +293,25 @@ fn normalize_ref(expr: &Expr<X, Normalized<'static>>) -> Expr<X, X> {
             let ys = ys.iter().cloned();
             Done(NEListLit(xs.chain(ys).collect()))
         }
-        Merge(RecordLit(handlers), UnionLit(k, v, _), _) => {
-            match handlers.get(&k) {
+        Merge(RecordLit(handlers), UnionLit(l, v, _), _) => {
+            match handlers.get(&l) {
                 Some(h) => Continue(App(h.clone(), vec![v.clone()])),
                 None => DoneAsIs,
             }
         }
+        Merge(RecordLit(handlers), UnionConstructor(l, _), _) => {
+            match handlers.get(&l) {
+                Some(h) => DoneRefSub(h),
+                None => DoneAsIs,
+            }
+        }
         Field(RecordLit(kvs), l) => match kvs.get(&l) {
             Some(r) => DoneRefSub(r),
             None => DoneAsIs,
         },
+        Field(UnionType(kts), l) => {
+            Done(UnionConstructor(l.clone(), kts.clone()))
+        }
         Projection(_, ls) if ls.is_empty() => {
             Done(RecordLit(std::collections::BTreeMap::new()))
         }
@@ -349,7 +366,7 @@ mod spec_tests {
     }
 
     norm!(success_haskell_tutorial_access_0, "haskell-tutorial/access/0");
-    // norm!(success_haskell_tutorial_access_1, "haskell-tutorial/access/1");
+    norm!(success_haskell_tutorial_access_1, "haskell-tutorial/access/1");
     // norm!(success_haskell_tutorial_combineTypes_0, "haskell-tutorial/combineTypes/0");
     // norm!(success_haskell_tutorial_combineTypes_1, "haskell-tutorial/combineTypes/1");
     // norm!(success_haskell_tutorial_prefer_0, "haskell-tutorial/prefer/0");
@@ -560,7 +577,8 @@ mod spec_tests {
     norm!(success_unit_ListReverse, "unit/ListReverse");
     norm!(success_unit_ListReverseEmpty, "unit/ListReverseEmpty");
     norm!(success_unit_ListReverseTwo, "unit/ListReverseTwo");
-    // norm!(success_unit_Merge, "unit/Merge");
+    norm!(success_unit_Merge, "unit/Merge");
+    norm!(success_unit_MergeEmptyAlternative, "unit/MergeEmptyAlternative");
     norm!(success_unit_MergeNormalizeArguments, "unit/MergeNormalizeArguments");
     norm!(success_unit_MergeWithType, "unit/MergeWithType");
     norm!(success_unit_MergeWithTypeNormalizeArguments, "unit/MergeWithTypeNormalizeArguments");
diff --git a/dhall_core/src/core.rs b/dhall_core/src/core.rs
index 075ef81..2dfa4d8 100644
--- a/dhall_core/src/core.rs
+++ b/dhall_core/src/core.rs
@@ -190,6 +190,8 @@ pub enum ExprF<SubExpr, Label, Note, Embed> {
     UnionType(BTreeMap<Label, Option<SubExpr>>),
     ///  `< k1 = t1, k2 : t2, k3 >`
     UnionLit(Label, SubExpr, BTreeMap<Label, Option<SubExpr>>),
+    ///  `< k1 : t1, k2 >.k1`
+    UnionConstructor(Label, BTreeMap<Label, Option<SubExpr>>),
     ///  `merge x y : t`
     Merge(SubExpr, SubExpr, Option<SubExpr>),
     ///  `e.x`
diff --git a/dhall_core/src/printer.rs b/dhall_core/src/printer.rs
index bb3c427..4d1ae2d 100644
--- a/dhall_core/src/printer.rs
+++ b/dhall_core/src/printer.rs
@@ -92,9 +92,9 @@ impl<SE: Display + Clone, N, E: Display> Display for ExprF<SE, Label, N, E> {
                 write!(f, "{} = {}", k, v)
             })?,
             UnionType(a) => fmt_list("< ", " | ", " >", a, f, |(k, v), f| {
-                write!(f, "{} : ", k)?;
+                write!(f, "{}", k)?;
                 if let Some(v) = v {
-                    v.fmt(f)?
+                    write!(f, ": {}", v)?;
                 }
                 Ok(())
             })?,
@@ -108,6 +108,16 @@ impl<SE: Display + Clone, N, E: Display> Display for ExprF<SE, Label, N, E> {
                 }
                 f.write_str(" >")?
             }
+            UnionConstructor(x, map) => {
+                fmt_list("< ", " | ", " >", map, f, |(k, v), f| {
+                    write!(f, "{}", k)?;
+                    if let Some(v) = v {
+                        write!(f, ": {}", v)?;
+                    }
+                    Ok(())
+                })?;
+                write!(f, ".{}", x)?
+            }
             Embed(a) => a.fmt(f)?,
             Note(_, b) => b.fmt(f)?,
         }
diff --git a/dhall_core/src/visitor.rs b/dhall_core/src/visitor.rs
index 1ea3fb1..c123275 100644
--- a/dhall_core/src/visitor.rs
+++ b/dhall_core/src/visitor.rs
@@ -178,11 +178,14 @@ where
             RecordType(kts) => RecordType(btmap(kts, v)?),
             RecordLit(kvs) => RecordLit(btmap(kvs, v)?),
             UnionType(kts) => UnionType(btoptmap(kts, v)?),
-            UnionLit(k, x, kvs) => UnionLit(
+            UnionLit(k, x, kts) => UnionLit(
                 v.visit_label(k)?,
                 v.visit_subexpr(x)?,
-                btoptmap(kvs, v)?,
+                btoptmap(kts, v)?,
             ),
+            UnionConstructor(x, kts) => {
+                UnionConstructor(v.visit_label(x)?, btoptmap(kts, v)?)
+            }
             Merge(x, y, t) => Merge(
                 v.visit_subexpr(x)?,
                 v.visit_subexpr(y)?,
-- 
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