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-rw-r--r--src/libexpr/nixexpr.cc39
1 files changed, 39 insertions, 0 deletions
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index a6cde127c..7502fd166 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -287,6 +287,45 @@ void checkVarDefs(const ATermMap & defs, Expr e)
}
+struct Canonicalise : TermFun
+{
+ ATerm operator () (ATerm e)
+ {
+ /* Remove position info. */
+ ATerm path;
+ int line, column;
+ if (matchPos(e, path, line, column))
+ return makeNoPos();
+
+ /* Sort attribute sets. */
+ ATermList _;
+ if (matchAttrs(e, _)) {
+ ATermMap attrs;
+ queryAllAttrs(e, attrs);
+ StringSet names;
+ for (ATermMap::const_iterator i = attrs.begin(); i != attrs.end(); ++i)
+ names.insert(aterm2String(i->key));
+
+ ATermList attrs2 = ATempty;
+ for (StringSet::reverse_iterator i = names.rbegin(); i != names.rend(); ++i)
+ attrs2 = ATinsert(attrs2,
+ makeBind(toATerm(*i), attrs.get(toATerm(*i)), makeNoPos()));
+
+ return makeAttrs(attrs2);
+ }
+
+ return e;
+ }
+};
+
+
+Expr canonicaliseExpr(Expr & e)
+{
+ Canonicalise canonicalise;
+ return bottomupRewrite(canonicalise, e);
+}
+
+
Expr makeBool(bool b)
{
return b ? eTrue : eFalse;