From d315210612a8d5eb52654407903544b72222130b Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Fri, 22 Sep 2006 14:55:19 +0000 Subject: * 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). --- src/libexpr/primops.cc | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'src/libexpr') 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); -- cgit 1.4.1