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authorEelco Dolstra <e.dolstra@tudelft.nl>2005-07-19T11·48+0000
committerEelco Dolstra <e.dolstra@tudelft.nl>2005-07-19T11·48+0000
commit0f827cc6076ae3c395537a0c9bd806b0d42947c2 (patch)
tree13c7e2090562d1e2cb02aade854a7599f4072275 /src
parent2135e7c0417b366b4161d01ebf794d25e96b61ba (diff)
* Prevent repeated wrapping of closed terms
  (closed(closed(closed(...)))) since this reduces performance by
  producing bigger terms and killing caching (which incidentally also
  prevents useful infinite recursion detection).

Diffstat (limited to 'src')
-rw-r--r--src/libexpr/nixexpr.cc7
1 files changed, 6 insertions, 1 deletions
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 5c67b74ca6c6..289e923c3311 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -233,7 +233,12 @@ Expr substitute(const ATermMap & subs, Expr e)
 
     if (matchVar(e, name)) {
         Expr sub = subs.get(name);
-        return sub ? makeClosed(sub) : e;
+        Expr wrapped;
+        /* Add a "closed" wrapper around terms that aren't already
+           closed.  The check is necessary to prevent repeated
+           wrapping, e.g., closed(closed(closed(...))), which kills
+           caching. */
+        return sub ? (matchClosed(sub, wrapped) ? sub : makeClosed(sub)) : e;
     }
 
     /* In case of a function, filter out all variables bound by this