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authorEelco Dolstra <e.dolstra@tudelft.nl>2011-07-13T12·19+0000
committerEelco Dolstra <e.dolstra@tudelft.nl>2011-07-13T12·19+0000
commit0a623a10c7e89a80b6dc74445a0ae6240f65723e (patch)
tree1c7a415095c4851c69d9b4c5dd1fea46a961a37c /src/libexpr/nixexpr.cc
parent2b9e29b1c8b6b8e4884a46a3ba71ee795f1f97cd (diff)
* Allow a default value in attribute selection by writing
    x.y.z or default

  (as originally proposed in
  https://mail.cs.uu.nl/pipermail/nix-dev/2009-September/002989.html).

  For instance, an expression like

    stdenv.lib.attrByPath ["features" "ckSched"] false args

  can now be written as

    args.features.ckSched or false


Diffstat (limited to 'src/libexpr/nixexpr.cc')
-rw-r--r--src/libexpr/nixexpr.cc2
1 files changed, 2 insertions, 0 deletions
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 2632d9f3ff8b..c52a413916a7 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -44,6 +44,7 @@ void ExprVar::show(std::ostream & str)
 void ExprSelect::show(std::ostream & str)
 {
     str << "(" << *e << ")." << showAttrPath(attrPath);
+    if (def) str << " or " << *def;
 }
 
 void ExprOpHasAttr::show(std::ostream & str)
@@ -211,6 +212,7 @@ void ExprVar::bindVars(const StaticEnv & env)
 void ExprSelect::bindVars(const StaticEnv & env)
 {
     e->bindVars(env);
+    if (def) def->bindVars(env);
 }
 
 void ExprOpHasAttr::bindVars(const StaticEnv & env)