From 5812a53cc9241703bd35586da0036dc170ab3721 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Sat, 20 Apr 2019 23:07:00 +0200
Subject: Implement more normalization simplifications

---
 dhall/src/normalize.rs | 25 ++++++++++++++++---------
 dhall_core/src/text.rs | 51 ++++++++++++++++++++++++--------------------------
 2 files changed, 40 insertions(+), 36 deletions(-)

diff --git a/dhall/src/normalize.rs b/dhall/src/normalize.rs
index ec25010..9e7c531 100644
--- a/dhall/src/normalize.rs
+++ b/dhall/src/normalize.rs
@@ -667,11 +667,16 @@ fn normalize_whnf(ctx: NormalizationContext, expr: InputSubExpr) -> WHNF {
             match b {
                 WHNF::BoolLit(true) => normalize_whnf(ctx, e1.clone()),
                 WHNF::BoolLit(false) => normalize_whnf(ctx, e2.clone()),
-                _ => normalize_last_layer(ExprF::BoolIf(
-                    b,
-                    normalize_whnf(ctx.clone(), e1.clone()),
-                    normalize_whnf(ctx, e2.clone()),
-                )),
+                b => {
+                    let e1 = normalize_whnf(ctx.clone(), e1.clone());
+                    let e2 = normalize_whnf(ctx, e2.clone());
+                    match (e1, e2) {
+                        (WHNF::BoolLit(true), WHNF::BoolLit(false)) => b,
+                        (e1, e2) => {
+                            normalize_last_layer(ExprF::BoolIf(b, e1, e2))
+                        }
+                    }
+                }
             }
         }
         expr => {
@@ -736,6 +741,8 @@ fn normalize_last_layer(expr: ExprF<WHNF, Label, X, X>) -> WHNF {
             x.append(&mut y);
             TextLit(x)
         }
+        ExprF::BinOp(TextAppend, TextLit(x), y) if x.is_empty() => y,
+        ExprF::BinOp(TextAppend, x, TextLit(y)) if y.is_empty() => x,
 
         ExprF::Field(UnionType(ctx, kts), l) => UnionConstructor(ctx, l, kts),
         ExprF::Field(RecordLit(mut kvs), l) => match kvs.remove(&l) {
@@ -981,7 +988,7 @@ mod spec_tests {
     // norm!(success_unit_IfAlternativesIdentical, "unit/IfAlternativesIdentical");
     norm!(success_unit_IfFalse, "unit/IfFalse");
     norm!(success_unit_IfNormalizePredicateAndBranches, "unit/IfNormalizePredicateAndBranches");
-    // norm!(success_unit_IfTrivial, "unit/IfTrivial");
+    norm!(success_unit_IfTrivial, "unit/IfTrivial");
     norm!(success_unit_IfTrue, "unit/IfTrue");
     norm!(success_unit_Integer, "unit/Integer");
     norm!(success_unit_IntegerNegative, "unit/IntegerNegative");
@@ -1075,9 +1082,9 @@ mod spec_tests {
     norm!(success_unit_OperatorPlusNormalizeArguments, "unit/OperatorPlusNormalizeArguments");
     norm!(success_unit_OperatorPlusOneAndOne, "unit/OperatorPlusOneAndOne");
     norm!(success_unit_OperatorPlusRhsZero, "unit/OperatorPlusRhsZero");
-    // norm!(success_unit_OperatorTextConcatenateLhsEmpty, "unit/OperatorTextConcatenateLhsEmpty");
-    // norm!(success_unit_OperatorTextConcatenateNormalizeArguments, "unit/OperatorTextConcatenateNormalizeArguments");
-    // norm!(success_unit_OperatorTextConcatenateRhsEmpty, "unit/OperatorTextConcatenateRhsEmpty");
+    norm!(success_unit_OperatorTextConcatenateLhsEmpty, "unit/OperatorTextConcatenateLhsEmpty");
+    norm!(success_unit_OperatorTextConcatenateNormalizeArguments, "unit/OperatorTextConcatenateNormalizeArguments");
+    norm!(success_unit_OperatorTextConcatenateRhsEmpty, "unit/OperatorTextConcatenateRhsEmpty");
     norm!(success_unit_OperatorTextConcatenateTextText, "unit/OperatorTextConcatenateTextText");
     norm!(success_unit_OperatorTimesLhsOne, "unit/OperatorTimesLhsOne");
     norm!(success_unit_OperatorTimesLhsZero, "unit/OperatorTimesLhsZero");
diff --git a/dhall_core/src/text.rs b/dhall_core/src/text.rs
index ff5c441..83643d9 100644
--- a/dhall_core/src/text.rs
+++ b/dhall_core/src/text.rs
@@ -1,5 +1,4 @@
 use std::iter::FromIterator;
-use std::ops::Add;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct InterpolatedText<SubExpr> {
@@ -33,6 +32,16 @@ pub enum InterpolatedTextContents<SubExpr> {
     Expr(SubExpr),
 }
 
+impl<SubExpr> InterpolatedTextContents<SubExpr> {
+    pub fn is_empty(&self) -> bool {
+        use InterpolatedTextContents::{Expr, Text};
+        match self {
+            Expr(_) => false,
+            Text(s) => s.is_empty(),
+        }
+    }
+}
+
 impl<SubExpr> InterpolatedText<SubExpr> {
     pub fn traverse_ref<'a, SubExpr2, E, F>(
         &'a self,
@@ -51,13 +60,6 @@ impl<SubExpr> InterpolatedText<SubExpr> {
         })
     }
 
-    pub fn as_ref(&self) -> InterpolatedText<&SubExpr> {
-        InterpolatedText {
-            head: self.head.clone(),
-            tail: self.tail.iter().map(|(e, s)| (e, s.clone())).collect(),
-        }
-    }
-
     pub fn iter<'a>(
         &'a self,
     ) -> impl Iterator<Item = InterpolatedTextContents<SubExpr>> + 'a
@@ -65,24 +67,26 @@ impl<SubExpr> InterpolatedText<SubExpr> {
         SubExpr: Clone,
     {
         use std::iter::once;
-        once(InterpolatedTextContents::Text(self.head.clone())).chain(
-            self.tail.iter().flat_map(|(e, s)| {
-                once(InterpolatedTextContents::Expr(SubExpr::clone(e)))
-                    .chain(once(InterpolatedTextContents::Text(s.clone())))
-            }),
-        )
+        use InterpolatedTextContents::{Expr, Text};
+        once(Text(self.head.clone()))
+            .chain(self.tail.iter().flat_map(|(e, s)| {
+                once(Expr(SubExpr::clone(e))).chain(once(Text(s.clone())))
+            }))
+            .filter(|c| !c.is_empty())
     }
 
     pub fn into_iter(
         self,
     ) -> impl Iterator<Item = InterpolatedTextContents<SubExpr>> {
         use std::iter::once;
-        once(InterpolatedTextContents::Text(self.head)).chain(
-            self.tail.into_iter().flat_map(|(e, s)| {
-                once(InterpolatedTextContents::Expr(e))
-                    .chain(once(InterpolatedTextContents::Text(s)))
-            }),
-        )
+        use InterpolatedTextContents::{Expr, Text};
+        once(Text(self.head))
+            .chain(
+                self.tail
+                    .into_iter()
+                    .flat_map(|(e, s)| once(Expr(e)).chain(once(Text(s)))),
+            )
+            .filter(|c| !c.is_empty())
     }
 }
 
@@ -110,10 +114,3 @@ impl<SubExpr> FromIterator<InterpolatedTextContents<SubExpr>>
         res
     }
 }
-
-impl<SubExpr: Clone> Add for &InterpolatedText<SubExpr> {
-    type Output = InterpolatedText<SubExpr>;
-    fn add(self, rhs: &InterpolatedText<SubExpr>) -> Self::Output {
-        self.iter().chain(rhs.iter()).collect()
-    }
-}
-- 
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