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authorEelco Dolstra <e.dolstra@tudelft.nl>2006-09-22T14·55+0000
committerEelco Dolstra <e.dolstra@tudelft.nl>2006-09-22T14·55+0000
commitd315210612a8d5eb52654407903544b72222130b (patch)
treeedf5de3774a9a4faca84268b2c3ed2e5f3d6d175 /src
parentc02a44183fcff7c28cfed1c84c142cc2cf80f167 (diff)
* Added a builtin function `isList' to test whether a value is a list.
  With this primitive, a list-flattening function can be implemented
  (NIX-55, example is in tests/lang/eval-okay-flatten.nix).

Diffstat (limited to 'src')
-rw-r--r--src/libexpr/primops.cc9
1 files changed, 9 insertions, 0 deletions
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index b05082293fb7..190d587330d1 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -521,6 +521,14 @@ static Expr primIsNull(EvalState & state, const ATermVector & args)
 }
 
 
+/* Determine whether the argument is a list. */
+static Expr primIsList(EvalState & state, const ATermVector & args)
+{
+    ATermList list;
+    return makeBool(matchList(evalExpr(state, args[0]), list));
+}
+
+
 static Path findDependency(Path dir, string dep)
 {
     if (dep[0] == '/') throw EvalError(
@@ -782,6 +790,7 @@ void EvalState::addPrimOps()
     addPrimOp("__toXML", 1, primToXML);
     addPrimOp("__toFile", 1, primToFile);
     addPrimOp("isNull", 1, primIsNull);
+    addPrimOp("__isList", 1, primIsList);
     addPrimOp("dependencyClosure", 1, primDependencyClosure);
     addPrimOp("abort", 1, primAbort);
     addPrimOp("__head", 1, primHead);