From 7e523ae1903ae2d8bca8b3a8352167d7bac5b2b5 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Mon, 14 Sep 2020 23:09:22 +0100
Subject: spec: Enable `with` optimizations

---
 dhall/src/syntax/ast/span.rs      |  1 -
 dhall/src/syntax/binary/decode.rs | 21 +++++++++++++++++++++
 dhall/src/syntax/binary/encode.rs |  4 ++++
 dhall/src/syntax/text/parser.rs   | 26 +++++---------------------
 dhall/src/syntax/text/printer.rs  |  4 ++++
 5 files changed, 34 insertions(+), 22 deletions(-)

(limited to 'dhall/src/syntax')

diff --git a/dhall/src/syntax/ast/span.rs b/dhall/src/syntax/ast/span.rs
index ab3279b..b0c7b5a 100644
--- a/dhall/src/syntax/ast/span.rs
+++ b/dhall/src/syntax/ast/span.rs
@@ -21,7 +21,6 @@ pub enum Span {
     /// Desugarings
     DuplicateRecordFieldsSugar,
     DottedFieldSugar,
-    WithSugar,
     RecordPunSugar,
     /// For expressions obtained from decoding binary
     Decoded,
diff --git a/dhall/src/syntax/binary/decode.rs b/dhall/src/syntax/binary/decode.rs
index 195bd0a..d360949 100644
--- a/dhall/src/syntax/binary/decode.rs
+++ b/dhall/src/syntax/binary/decode.rs
@@ -434,6 +434,27 @@ fn cbor_value_to_dhall(data: &cbor::Value) -> Result<DecodedExpr, DecodeError> {
                 let x = cbor_value_to_dhall(&x)?;
                 EmptyListLit(x)
             }
+            [U64(29), x, labels, y] => {
+                let x = cbor_value_to_dhall(&x)?;
+                let y = cbor_value_to_dhall(&y)?;
+                let labels = match labels {
+                    Array(labels) => labels
+                        .iter()
+                        .map(|s| match s {
+                            String(s) => Ok(Label::from(s.as_str())),
+                            _ => Err(DecodeError::WrongFormatError(
+                                "with".to_owned(),
+                            )),
+                        })
+                        .collect::<Result<_, _>>()?,
+                    _ => {
+                        return Err(DecodeError::WrongFormatError(
+                            "with".to_owned(),
+                        ))
+                    }
+                };
+                Op(With(x, labels, y))
+            }
             _ => {
                 return Err(DecodeError::WrongFormatError(format!(
                     "{:?}",
diff --git a/dhall/src/syntax/binary/encode.rs b/dhall/src/syntax/binary/encode.rs
index b6bbabe..33c7fa5 100644
--- a/dhall/src/syntax/binary/encode.rs
+++ b/dhall/src/syntax/binary/encode.rs
@@ -171,6 +171,10 @@ where
         Op(Completion(x, y)) => {
             ser_seq!(ser; tag(3), tag(13), expr(x), expr(y))
         }
+        Op(With(x, ls, y)) => {
+            let ls: Vec<_> = ls.iter().map(label).collect();
+            ser_seq!(ser; tag(29), expr(x), ls, expr(y))
+        }
         Import(import) => serialize_import(ser, import),
     }
 }
diff --git a/dhall/src/syntax/text/parser.rs b/dhall/src/syntax/text/parser.rs
index 06c1ac3..377f5e4 100644
--- a/dhall/src/syntax/text/parser.rs
+++ b/dhall/src/syntax/text/parser.rs
@@ -105,26 +105,6 @@ fn insert_recordlit_entry(map: &mut BTreeMap<Label, Expr>, l: Label, e: Expr) {
     }
 }
 
-fn desugar_with_expr(x: Expr, labels: &[Label], y: Expr) -> Expr {
-    use crate::operations::BinOp::RightBiasedRecordMerge;
-    let expr = |k| Expr::new(k, Span::WithSugar);
-    match labels {
-        [] => y,
-        [l, rest @ ..] => {
-            let res = desugar_with_expr(
-                expr(Op(Field(x.clone(), l.clone()))),
-                rest,
-                y,
-            );
-            expr(Op(BinOp(
-                RightBiasedRecordMerge,
-                x,
-                expr(RecordLit(once((l.clone(), res)).collect())),
-            )))
-        }
-    }
-}
-
 lazy_static::lazy_static! {
     static ref PRECCLIMBER: PrecClimber<Rule> = {
         use Rule::*;
@@ -778,7 +758,11 @@ impl DhallParser {
                 clauses.fold(
                     first,
                     |acc, (labels, e)| {
-                        desugar_with_expr(acc, &labels, e)
+                        spanned_union(
+                            acc.span(),
+                            e.span(),
+                            Op(With(acc, labels, e))
+                        )
                     }
                 )
             },
diff --git a/dhall/src/syntax/text/printer.rs b/dhall/src/syntax/text/printer.rs
index 8815d69..0c2eb2e 100644
--- a/dhall/src/syntax/text/printer.rs
+++ b/dhall/src/syntax/text/printer.rs
@@ -275,6 +275,10 @@ impl<SE: Display + Clone> Display for OpKind<SE> {
             Completion(a, b) => {
                 write!(f, "{}::{}", a, b)?;
             }
+            With(a, ls, b) => {
+                let ls = ls.iter().join(".");
+                write!(f, "{} with {} = {}", a, ls, b)?;
+            }
         }
         Ok(())
     }
-- 
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