4 files changed, 33 insertions, 3 deletions
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 40e05712bab1..50093d3fc010 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -26,9 +26,9 @@ typedef void (* PrimOpFun) (EvalState & state, const Pos & pos, Value * * args,
 struct PrimOp
 {
     PrimOpFun fun;
-    unsigned int arity;
+    size_t arity;
     Symbol name;
-    PrimOp(PrimOpFun fun, unsigned int arity, Symbol name)
+    PrimOp(PrimOpFun fun, size_t arity, Symbol name)
         : fun(fun), arity(arity), name(name) { }
 };
 
diff --git a/src/libexpr/local.mk b/src/libexpr/local.mk
index 5de9ccc6d011..620050a13b05 100644
--- a/src/libexpr/local.mk
+++ b/src/libexpr/local.mk
@@ -4,7 +4,7 @@ libexpr_NAME = libnixexpr
 
 libexpr_DIR := $(d)
 
-libexpr_SOURCES := $(wildcard $(d)/*.cc) $(d)/lexer-tab.cc $(d)/parser-tab.cc
+libexpr_SOURCES := $(wildcard $(d)/*.cc) $(wildcard $(d)/primops/*.cc) $(d)/lexer-tab.cc $(d)/parser-tab.cc
 
 libexpr_CXXFLAGS := -Wno-deprecated-register
 
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index aaef467c098b..816827d6abc2 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -10,6 +10,7 @@
 #include "util.hh"
 #include "value-to-json.hh"
 #include "value-to-xml.hh"
+#include "primops.hh"
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -1725,6 +1726,16 @@ static void prim_fetchTarball(EvalState & state, const Pos & pos, Value * * args
  *************************************************************/
 
 
+RegisterPrimOp::PrimOps * RegisterPrimOp::primOps;
+
+
+RegisterPrimOp::RegisterPrimOp(std::string name, size_t arity, PrimOpFun fun)
+{
+    if (!primOps) primOps = new PrimOps;
+    primOps->emplace_back(name, arity, fun);
+}
+
+
 void EvalState::createBaseEnv()
 {
     baseEnv.up = 0;
@@ -1889,6 +1900,10 @@ void EvalState::createBaseEnv()
     }
     addConstant("__nixPath", v);
 
+    if (RegisterPrimOp::primOps)
+        for (auto & primOp : *RegisterPrimOp::primOps)
+            addPrimOp(std::get<0>(primOp), std::get<1>(primOp), std::get<2>(primOp));
+
     /* Now that we've added all primops, sort the `builtins' set,
        because attribute lookups expect it to be sorted. */
     baseEnv.values[0]->attrs->sort();
diff --git a/src/libexpr/primops.hh b/src/libexpr/primops.hh
new file mode 100644
index 000000000000..39d23b04a5ce
--- /dev/null
+++ b/src/libexpr/primops.hh
@@ -0,0 +1,15 @@
+#include "eval.hh"
+
+#include <tuple>
+#include <vector>
+
+namespace nix {
+
+struct RegisterPrimOp
+{
+    typedef std::vector<std::tuple<std::string, size_t, PrimOpFun>> PrimOps;
+    static PrimOps * primOps;
+    RegisterPrimOp(std::string name, size_t arity, PrimOpFun fun);
+};
+
+}