* New builtin function "isFunction". You're not supposed to use it

;-)
* Channels: fix channels that are plain lists of derivations (like
  strategoxt-unstable) instead  of functions (like nixpkgs-unstable).
  This fixes the error message "error: the left-hand side of the
  function call is neither a function nor a primop (built-in
  operation) but a list".

corepkgs/channels/unpack.sh.in

@@ -24,7 +24,7 @@ for ((n = 0; n < ${#inputs[*]}; n += 2)); do
     @coreutils@/mv * ../$dirName # !!! hacky
     
     attrName=$(echo $dirName | @tr@ -- '- ' '__')
-    echo "$attrName = import ./$dirName {};" >> $expr
+    echo "$attrName = let e = import ./$dirName; in if builtins.isFunction e then e {} else e;" >> $expr
 done
 
 echo '} // {_combineChannels = true;}' >> $expr

src/libexpr/eval.cc

@@ -478,7 +478,7 @@ LocalNoInline(Expr evalCall(EvalState & state, Expr fun, Expr arg))
     }
 
     else throwTypeError(
-        "the left-hand side of the function call is neither a function nor a primop (built-in operation) but %1%",
+        "attempt to call something which is neither a function nor a primop (built-in operation) but %1%",
         showType(fun));
 }
 

src/libexpr/primops.cc

@@ -114,6 +114,18 @@ static Expr prim_isNull(EvalState & state, const ATermVector & args)
 }
 
 
+/* Determine whether the argument is a function. */
+static Expr prim_isFunction(EvalState & state, const ATermVector & args)
+{
+    Expr e = evalExpr(state, args[0]);
+    ATermList formals;
+    ATerm name, body, pos;
+    return makeBool(
+        matchFunction(e, formals, body, pos) ||
+        matchFunction1(e, name, body, pos));
+}
+
+
 static Path findDependency(Path dir, string dep)
 {
     if (dep[0] == '/') throw EvalError(
@@ -884,6 +896,7 @@ void EvalState::addPrimOps()
     // Miscellaneous
     addPrimOp("import", 1, prim_import);
     addPrimOp("isNull", 1, prim_isNull);
+    addPrimOp("__isFunction", 1, prim_isFunction);
     addPrimOp("dependencyClosure", 1, prim_dependencyClosure);
     addPrimOp("abort", 1, prim_abort);
     addPrimOp("throw", 1, prim_throw);