Handle quoted labels

3 files changed, 21 insertions, 8 deletions

diff --git a/dhall_core/src/label.rs b/dhall_core/src/label.rs
index 3633b93..8b371af 100644
--- a/dhall_core/src/label.rs
+++ b/dhall_core/src/label.rs
@@ -1,4 +1,3 @@
-use std::fmt::{self, Display};
 use std::rc::Rc;
 
 // The type for labels throughout the AST
@@ -25,12 +24,6 @@ impl From<Label> for String {
     }
 }
 
-impl Display for Label {
-    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        self.0.as_ref().fmt(f)
-    }
-}
-
 impl Label {
     pub fn from_str(s: &str) -> Label {
         Label(s.into())
diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index 165b393..8908c78 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -257,7 +257,12 @@ fn can_be_shortcutted(rule: Rule) -> bool {
 make_parser! {
     rule!(EOI<()>; raw_pair!(_) => ());
 
-    rule!(label_raw<Label>; captured_str!(s) => Label::from(s.trim().to_owned()));
+    rule!(simple_label<Label>; captured_str!(s) => Label::from(s.trim().to_owned()));
+    rule!(quoted_label<Label>; captured_str!(s) => Label::from(s.trim().to_owned()));
+    rule!(label_raw<Label>; children!(
+        [simple_label(l)] => l,
+        [quoted_label(l)] => l,
+    ));
 
     rule!(double_quote_literal<ParsedText>; children!(
         [double_quote_chunk(chunks..)] => {
diff --git a/dhall_core/src/printer.rs b/dhall_core/src/printer.rs
index 7b108d5..508c1c8 100644
--- a/dhall_core/src/printer.rs
+++ b/dhall_core/src/printer.rs
@@ -285,6 +285,21 @@ impl Display for Const {
     }
 }
 
+impl Display for Label {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        let s = String::from(self.clone());
+        let is_keyword = |s| match s {
+            "let" | "in" | "if" | "then" | "else" => true,
+            _ => false,
+        };
+        if s.chars().all(|c| c.is_ascii_alphanumeric()) && !is_keyword(&s) {
+            write!(f, "{}", s)
+        } else {
+            write!(f, "`{}`", s)
+        }
+    }
+}
+
 impl Display for Import {
     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
         use std::path::PathBuf;