diff --git a/src/main/scala/is/hail/expr/AST.scala b/src/main/scala/is/hail/expr/AST.scala
index 93719037e705..c101ec41633a 100644
--- a/src/main/scala/is/hail/expr/AST.scala
+++ b/src/main/scala/is/hail/expr/AST.scala
@@ -668,7 +668,7 @@ case class Apply(posn: Position, fn: String, args: Array[AST]) extends AST(posn,
         for {
           irArgs <- anyFailAllFail(args.map(_.toIR(agg)))
           ir <- tryPrimOpConversion(args.map(_.`type`).zip(irArgs)).orElse(
-            IRFunctionRegistry.lookupFunction(fn, args.map(_.`type`))
+            IRFunctionRegistry.lookupConversion(fn, args.map(_.`type`))
               .map { irf => irf(irArgs) })
         } yield ir
     }
@@ -781,7 +781,7 @@ case class ApplyMethod(posn: Position, lhs: AST, method: String, args: Array[AST
       case _ =>
         for {
           irs <- anyFailAllFail((lhs +: args).map(_.toIR(agg)))
-          ir <- IRFunctionRegistry.lookupFunction(method, (lhs +: args).map(_.`type`))
+          ir <- IRFunctionRegistry.lookupConversion(method, (lhs +: args).map(_.`type`))
               .map { irf => irf(irs) }
         } yield ir
     }
diff --git a/src/main/scala/is/hail/expr/ir/Children.scala b/src/main/scala/is/hail/expr/ir/Children.scala
index 77aa8c256a43..9cc17183d98c 100644
--- a/src/main/scala/is/hail/expr/ir/Children.scala
+++ b/src/main/scala/is/hail/expr/ir/Children.scala
@@ -76,7 +76,7 @@ object Children {
       none
     case Die(message) =>
       none
-    case ApplyFunction(impl, args) =>
+    case Apply(_, args, _) =>
       args.toIndexedSeq
   }
 }
diff --git a/src/main/scala/is/hail/expr/ir/Copy.scala b/src/main/scala/is/hail/expr/ir/Copy.scala
index 413d12a06eb1..ee7eac163e38 100644
--- a/src/main/scala/is/hail/expr/ir/Copy.scala
+++ b/src/main/scala/is/hail/expr/ir/Copy.scala
@@ -104,8 +104,8 @@ object Copy {
         same
       case Die(message) =>
         same
-      case ApplyFunction(impl, args) =>
-        ApplyFunction(impl, children)
+      case Apply(fn, args, impl) =>
+        Apply(fn, children, impl)
     }
   }
 }
diff --git a/src/main/scala/is/hail/expr/ir/Emit.scala b/src/main/scala/is/hail/expr/ir/Emit.scala
index 438b8ef06bac..c61c0d47d442 100644
--- a/src/main/scala/is/hail/expr/ir/Emit.scala
+++ b/src/main/scala/is/hail/expr/ir/Emit.scala
@@ -501,7 +501,7 @@ private class Emit(
         present(fb.getArg[Boolean](i * 2 + 3))
       case Die(m) =>
         present(Code._throw(Code.newInstance[RuntimeException, String](m)))
-      case ApplyFunction(impl, args) =>
+      case Apply(fn, args, impl) =>
         val meth = methods.getOrElseUpdate(impl, {
           impl.argTypes.foreach(_.clear())
           (impl.argTypes, args.map(a => a.typ)).zipped.foreach(_.unify(_))
diff --git a/src/main/scala/is/hail/expr/ir/IR.scala b/src/main/scala/is/hail/expr/ir/IR.scala
index 8cc39ea61025..961ff67ba624 100644
--- a/src/main/scala/is/hail/expr/ir/IR.scala
+++ b/src/main/scala/is/hail/expr/ir/IR.scala
@@ -84,4 +84,4 @@ final case class InMissingness(i: Int) extends IR { val typ: Type = TBoolean() }
 // FIXME: should be type any
 final case class Die(message: String) extends IR { val typ = TVoid }
 
-final case class ApplyFunction(implementation: IRFunction, args: Seq[IR]) extends IR { val typ = implementation.returnType }
+final case class Apply(function: String, args: Seq[IR], var implementation: IRFunction = null) extends IR { def typ = implementation.returnType }
diff --git a/src/main/scala/is/hail/expr/ir/Infer.scala b/src/main/scala/is/hail/expr/ir/Infer.scala
index 4465c087e2aa..811219d414b1 100644
--- a/src/main/scala/is/hail/expr/ir/Infer.scala
+++ b/src/main/scala/is/hail/expr/ir/Infer.scala
@@ -1,5 +1,6 @@
 package is.hail.expr.ir
 
+import is.hail.expr.ir.functions.IRFunctionRegistry
 import is.hail.expr.types._
 
 object Infer {
@@ -174,9 +175,11 @@ object Infer {
         assert(typ != null)
       case InMissingness(i) =>
       case Die(msg) =>
-      case ApplyFunction(impl, args) =>
+      case x@Apply(fn, args, impl) =>
         args.foreach(infer(_))
-        assert(args.map(_.typ).zip(impl.argTypes).forall {case (i, j) => j.unify(i)})
+        if (impl == null)
+          x.implementation = IRFunctionRegistry.lookupFunction(fn, args.map(_.typ)).get
+        assert(args.map(_.typ).zip(x.implementation.argTypes).forall {case (i, j) => j.unify(i)})
     }
   }
 
diff --git a/src/main/scala/is/hail/expr/ir/Recur.scala b/src/main/scala/is/hail/expr/ir/Recur.scala
index d93a9a9bf1b5..41af8a885f15 100644
--- a/src/main/scala/is/hail/expr/ir/Recur.scala
+++ b/src/main/scala/is/hail/expr/ir/Recur.scala
@@ -41,6 +41,6 @@ object Recur {
     case In(i, typ) => ir
     case InMissingness(i) => ir
     case Die(message) => ir
-    case ApplyFunction(impl, args) => ApplyFunction(impl, args.map(f))
+    case Apply(fn, args, impl) => Apply(fn, args.map(f), impl)
   }
 }
diff --git a/src/main/scala/is/hail/expr/ir/functions/Functions.scala b/src/main/scala/is/hail/expr/ir/functions/Functions.scala
index 0ab43c664a7f..71b39d3e3265 100644
--- a/src/main/scala/is/hail/expr/ir/functions/Functions.scala
+++ b/src/main/scala/is/hail/expr/ir/functions/Functions.scala
@@ -7,38 +7,60 @@ import is.hail.utils._
 import is.hail.asm4s.coerce
 
 import scala.collection.mutable
-import scala.reflect.ClassTag
 
 object IRFunctionRegistry {
 
-  val registry: mutable.Map[String, Seq[(Seq[Type], Seq[IR] => IR)]] = mutable.Map().withDefaultValue(Seq.empty)
+  val irRegistry: mutable.Map[String, Seq[(Seq[Type], Seq[IR] => IR)]] = mutable.Map().withDefaultValue(Seq.empty)
+
+  val codeRegistry: mutable.Map[String, Seq[(Seq[Type], IRFunction)]] = mutable.Map().withDefaultValue(Seq.empty)
 
   def addIRFunction(f: IRFunction) {
-    val l = registry(f.name)
-    registry.put(f.name,
-      l :+ (f.argTypes, { args: Seq[IR] =>
-        ApplyFunction(f, args)
-      }))
+    val l = codeRegistry(f.name)
+    codeRegistry.put(f.name,
+      l :+ (f.argTypes, f))
   }
 
   def addIR(name: String, types: Seq[Type], f: Seq[IR] => IR) {
-    val l = registry(name)
-    registry.put(name, l :+ ((types, f)))
+    val l = irRegistry(name)
+    irRegistry.put(name, l :+ ((types, f)))
+  }
+
+  def lookupFunction(name: String, args: Seq[Type]): Option[IRFunction] = {
+    val validF = codeRegistry(name).flatMap { case (ts, f) =>
+      if (ts.length == args.length) {
+        ts.foreach(_.clear())
+        if ((ts, args).zipped.forall(_.unify(_)))
+          Some(f)
+        else
+          None
+      } else
+        None
+    }
+
+    validF match {
+      case Seq() => None
+      case Seq(x) => Some(x)
+      case _ => fatal(s"Multiple IRFunctions found that satisfy $name$args.")
+    }
   }
 
-  def lookupFunction(name: String, args: Seq[Type]): Option[Seq[IR] => IR] = {
+  def lookupConversion(name: String, args: Seq[Type]): Option[Seq[IR] => IR] = {
     assert(args.forall(_ != null))
-    val validMethods = registry(name).flatMap { case (ts, f) =>
+    val validIR = irRegistry(name).flatMap { case (ts, f) =>
       if (ts.length == args.length) {
         ts.foreach(_.clear())
         if ((ts, args).zipped.forall(_.unify(_)))
           Some(f)
         else
           None
-      } else {
+      } else
         None
-      }
     }
+
+    val validMethods = validIR ++ lookupFunction(name, args).map { f =>
+      { args: Seq[IR] => Apply(name, args, f) }
+    }
+
     validMethods match {
       case Seq() => None
       case Seq(x) => Some(x)
diff --git a/src/test/scala/is/hail/expr/ir/CompileSuite.scala b/src/test/scala/is/hail/expr/ir/CompileSuite.scala
index 8a76c7130d22..79ad29f764c7 100644
--- a/src/test/scala/is/hail/expr/ir/CompileSuite.scala
+++ b/src/test/scala/is/hail/expr/ir/CompileSuite.scala
@@ -494,7 +494,7 @@ class CompileSuite {
     val a2t = TArray(TString())
     val a1 = In(0, TArray(TInt32()))
     val a2 = In(1, TArray(TString()))
-    val min = IRFunctionRegistry.lookupFunction("min", Seq(TArray(TInt32()))).get
+    val min = IRFunctionRegistry.lookupConversion("min", Seq(TArray(TInt32()))).get
     val range = ArrayRange(I32(0), min(Seq(MakeArray(Seq(ArrayLen(a1), ArrayLen(a2))))), I32(1))
     val ir = ArrayMap(range, "i", MakeTuple(Seq(ArrayRef(a1, Ref("i")), ArrayRef(a2, Ref("i")))))
     val region = Region()
diff --git a/src/test/scala/is/hail/expr/ir/FunctionSuite.scala b/src/test/scala/is/hail/expr/ir/FunctionSuite.scala
index 5e6302ae4119..f597ee23f9f1 100644
--- a/src/test/scala/is/hail/expr/ir/FunctionSuite.scala
+++ b/src/test/scala/is/hail/expr/ir/FunctionSuite.scala
@@ -58,10 +58,8 @@ class FunctionSuite {
     fb.result(Some(new PrintWriter(System.out)))()
   }
 
-  def lookup(meth: String, types: Type*)(irs: IR*): IR = {
-    val possible = IRFunctionRegistry.registry(meth)
-    IRFunctionRegistry.lookupFunction(meth, types).get(irs)
-  }
+  def lookup(meth: String, types: Type*)(irs: IR*): IR =
+    IRFunctionRegistry.lookupConversion(meth, types).get(irs)
 
   @Test
   def testCodeFunction() {
@@ -110,10 +108,10 @@ class FunctionSuite {
 
   @Test
   def testVariableUnification() {
-    assert(IRFunctionRegistry.lookupFunction("testCodeUnification", Seq(TInt32(), TInt32())).isDefined)
-    assert(IRFunctionRegistry.lookupFunction("testCodeUnification", Seq(TInt64(), TInt32())).isEmpty)
-    assert(IRFunctionRegistry.lookupFunction("testCodeUnification", Seq(TInt64(), TInt64())).isEmpty)
-    assert(IRFunctionRegistry.lookupFunction("testCodeUnification2", Seq(TArray(TInt32()))).isDefined)
+    assert(IRFunctionRegistry.lookupConversion("testCodeUnification", Seq(TInt32(), TInt32())).isDefined)
+    assert(IRFunctionRegistry.lookupConversion("testCodeUnification", Seq(TInt64(), TInt32())).isEmpty)
+    assert(IRFunctionRegistry.lookupConversion("testCodeUnification", Seq(TInt64(), TInt64())).isEmpty)
+    assert(IRFunctionRegistry.lookupConversion("testCodeUnification2", Seq(TArray(TInt32()))).isDefined)
   }
 
   @Test