From cd9d10d4e3a646b6c0fef9e13a8efb2995fc50cd Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <e.dolstra@tudelft.nl>
Date: Thu, 11 Oct 2007 20:02:08 +0000
Subject: [PATCH] * Caching of parse results for fairer comparisons.

---
 src/libexpr/eval.hh  | 2 ++
 src/libexpr/parser.y | 7 ++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 08b685fd0..4692bfd27 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -41,6 +41,8 @@ struct EvalState
     bool cacheTerms;
     bool strictMode;
 
+    ATermMap parsings; /* path -> expr mapping */
+
     EvalState();
 
     void addPrimOps();
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 82b24cd07..b1284b4b0 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -383,8 +383,13 @@ Expr parseExprFromFile(EvalState & state, Path path)
     if (S_ISDIR(st.st_mode))
         path = canonPath(path + "/default.nix");
 
+    Expr cached = state.parsings.get(toATerm(path));
+    if (cached) return cached;
+
     /* Read and parse the input file. */
-    return parse(state, readFile(path).c_str(), path, dirOf(path));
+    cached = parse(state, readFile(path).c_str(), path, dirOf(path));
+    state.parsings.set(toATerm(path), cached);
+    return cached;
 }