From e4bdadabeda8ff8dbae0376f9d1c25478b8c8821 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Thu, 15 Aug 2019 15:33:53 +0200
Subject: Use precedence climbing to parse expressions with operators

This speeds up parsing around 30%
---
 dhall_generated_parser/build.rs | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

(limited to 'dhall_generated_parser/build.rs')

diff --git a/dhall_generated_parser/build.rs b/dhall_generated_parser/build.rs
index 070aa9c..c562fad 100644
--- a/dhall_generated_parser/build.rs
+++ b/dhall_generated_parser/build.rs
@@ -51,6 +51,37 @@ fn main() -> std::io::Result<()> {
     }}"
     )?;
 
+    // Setup grammar for precedence climbing
+    rules.remove("operator_expression");
+    writeln!(&mut file, r##"
+        import_alt = {{ "?" ~ whsp1 }}
+        bool_or = {{ "||" }}
+        natural_plus = {{ "+" ~ whsp1 }}
+        text_append = {{ "++" }}
+        list_append = {{ "#" }}
+        bool_and = {{ "&&" }}
+        natural_times = {{ "*" }}
+        bool_eq = {{ "==" }}
+        bool_ne = {{ "!=" }}
+
+        operator = _{{
+            equivalent |
+            bool_ne |
+            bool_eq |
+            natural_times |
+            combine_types |
+            prefer |
+            combine |
+            bool_and |
+            list_append |
+            text_append |
+            natural_plus |
+            bool_or |
+            import_alt
+        }}
+        operator_expression = {{ application_expression ~ (whsp ~ operator ~ whsp ~ application_expression)* }}
+    "##)?;
+
     writeln!(
         &mut file,
         "final_expression = ${{ SOI ~ complete_expression ~ EOI }}"
-- 
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