From 062fc44a93a18ee432e51db852290ab5849f4dd9 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Sat, 23 Mar 2019 23:24:11 +0100
Subject: Handle merge and record projection

---
 dhall_core/src/core.rs    | 15 ++++++++++-----
 dhall_core/src/parser.rs  | 21 +++++++++++++++++----
 dhall_core/src/printer.rs |  5 +++++
 3 files changed, 32 insertions(+), 9 deletions(-)

(limited to 'dhall_core')

diff --git a/dhall_core/src/core.rs b/dhall_core/src/core.rs
index bc5a666..502a9bc 100644
--- a/dhall_core/src/core.rs
+++ b/dhall_core/src/core.rs
@@ -241,8 +241,10 @@ pub enum Expr<Note, Embed> {
         SubExpr<Note, Embed>,
         Option<SubExpr<Note, Embed>>,
     ),
-    ///  `Field e x                                ~  e.x`
+    ///  e.x
     Field(SubExpr<Note, Embed>, Label),
+    ///  e.{ x, y, z }
+    Projection(SubExpr<Note, Embed>, Vec<Label>),
     /// Annotation on the AST. Unused for now but could hold e.g. file location information
     Note(Note, SubExpr<Note, Embed>),
     /// Embeds an import or the result of resolving the import
@@ -353,9 +355,9 @@ where
     };
     match e {
         Const(k) => Const(*k),
-        Var(V(x, n)) => Var(V(map_label(x), *n)),
-        Lam(x, t, b) => Lam(map_label(x), map(t), map_under_binder(x, b)),
-        Pi(x, t, b) => Pi(map_label(x), map(t), map_under_binder(x, b)),
+        Var(V(l, n)) => Var(V(map_label(l), *n)),
+        Lam(l, t, b) => Lam(map_label(l), map(t), map_under_binder(l, b)),
+        Pi(l, t, b) => Pi(map_label(l), map(t), map_under_binder(l, b)),
         App(f, args) => App(map(f), vec(args)),
         Let(l, t, a, b) => {
             Let(map_label(l), opt(t), map(a), map_under_binder(l, b))
@@ -378,7 +380,10 @@ where
         UnionType(kts) => UnionType(btmap(kts)),
         UnionLit(k, v, kvs) => UnionLit(map_label(k), map(v), btmap(kvs)),
         Merge(x, y, t) => Merge(map(x), map(y), opt(t)),
-        Field(r, x) => Field(map(r), map_label(x)),
+        Field(e, l) => Field(map(e), map_label(l)),
+        Projection(e, ls) => {
+            Projection(map(e), ls.iter().map(&map_label).collect())
+        }
         Note(n, e) => Note(map_note(n), map(e)),
         Embed(a) => Embed(map_embed(a)),
     }
diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index f959d2e..a62f861 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -19,6 +19,12 @@ pub type ParseError = pest::error::Error<Rule>;
 
 pub type ParseResult<T> = Result<T, ParseError>;
 
+#[derive(Debug)]
+enum Either<A, B> {
+    Left(A),
+    Right(B),
+}
+
 impl Builtin {
     pub fn parse(s: &str) -> Option<Self> {
         use self::Builtin::*;
@@ -649,13 +655,20 @@ make_parser! {
     rule!(selector_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), selector(rest..)] => {
-            rest.fold(first, |acc, e| bx(Expr::Field(acc, e)))
+            rest.fold(first, |acc, e| match e {
+                Either::Left(l) => bx(Expr::Field(acc, l)),
+                Either::Right(ls) => bx(Expr::Projection(acc, ls)),
+            })
         }
     ));
 
-    // TODO: handle record projection
-    rule!(selector<Label>; children!(
-        [label(l)] => l
+    rule!(selector<Either<Label, Vec<Label>>>; children!(
+        [label(l)] => Either::Left(l),
+        [labels(ls)] => Either::Right(ls),
+    ));
+
+    rule!(labels<Vec<Label>>; children!(
+        [label(ls..)] => ls.collect(),
     ));
 
     rule!(literal_expression<ParsedExpr> as expression; children!(
diff --git a/dhall_core/src/printer.rs b/dhall_core/src/printer.rs
index 5ecf5ce..d93336e 100644
--- a/dhall_core/src/printer.rs
+++ b/dhall_core/src/printer.rs
@@ -165,6 +165,11 @@ impl<S, A: Display> Expr<S, A> {
                 a.fmt_e(f)?;
                 write!(f, ".{}", b)
             }
+            &Projection(ref e, ref ls) => {
+                e.fmt_e(f)?;
+                write!(f, ".")?;
+                fmt_list("{ ", ", ", " }", ls, f, |l, f| write!(f, "{}", l))
+            }
             &Note(_, ref b) => b.fmt_e(f),
             a => a.fmt_f(f),
         }
-- 
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