diff --git a/c/containers/xvfuncs.c b/c/containers/xvfuncs.c
index b78ea6741..4b33b61ef 100644
--- a/c/containers/xvfuncs.c
+++ b/c/containers/xvfuncs.c
@@ -16,7 +16,7 @@ boxed_xval_t b_x_haskey_xfunc(boxed_xval_t* pmapval, boxed_xval_t* pkeyval) {
 }
 
 // ----------------------------------------------------------------
-boxed_xval_t b_x_length_xfunc(boxed_xval_t* pxval1) {
+boxed_xval_t i_x_length_xfunc(boxed_xval_t* pxval1) {
 	if (pxval1->xval.is_terminal) {
 		return box_ephemeral_val(
 			mv_from_int(1)
diff --git a/c/containers/xvfuncs.h b/c/containers/xvfuncs.h
index 94e0a2137..292821bb9 100644
--- a/c/containers/xvfuncs.h
+++ b/c/containers/xvfuncs.h
@@ -160,7 +160,7 @@ static inline boxed_xval_t b_x_typeof_xfunc(boxed_xval_t* pbxval1) {
 // ----------------------------------------------------------------
 boxed_xval_t b_x_haskey_xfunc(boxed_xval_t* pmapval, boxed_xval_t* pkeyval);
 
-boxed_xval_t b_x_length_xfunc(boxed_xval_t* pbxval1);
+boxed_xval_t i_x_length_xfunc(boxed_xval_t* pbxval1);
 
 // xxx to do (non-inline):
 //boxed_xval_t i_m_depth_xfunc(boxed_xval_t* pbxval1);
diff --git a/c/dsl/function_manager.c b/c/dsl/function_manager.c
index acdb38bfe..58c818c33 100644
--- a/c/dsl/function_manager.c
+++ b/c/dsl/function_manager.c
@@ -1149,17 +1149,15 @@ static rxval_evaluator_t* fmgr_alloc_xevaluator_from_variadic_func_name(
 // ----------------------------------------------------------------
 static rxval_evaluator_t* fmgr_alloc_xevaluator_from_unary_func_name(char* fnnm, rxval_evaluator_t* parg1) {
 	if (streq(fnnm, "ismap")) {
-		return rxval_evaluator_alloc_from_b_m_func(NULL/*xxx temp*/, parg1);
+		return rxval_evaluator_alloc_from_b_x_func(b_x_ismap_xfunc, parg1);
 	} else if (streq(fnnm, "isscalar")) {
-		return rxval_evaluator_alloc_from_b_m_func(NULL/*xxx temp*/, parg1);
+		return rxval_evaluator_alloc_from_b_m_func(b_x_isscalar_xfunc, parg1);
 	} else if (streq(fnnm, "isemptymap")) {
-		return rxval_evaluator_alloc_from_b_m_func(NULL/*xxx temp*/, parg1);
+		return rxval_evaluator_alloc_from_b_m_func(b_x_isemptymap_xfunc, parg1);
 	} else if (streq(fnnm, "isnonemptymap")) {
-		return rxval_evaluator_alloc_from_b_m_func(NULL/*xxx temp*/, parg1);
-	} else if (streq(fnnm, "haskey")) {
-		return rxval_evaluator_alloc_from_b_m_func(NULL/*xxx temp*/, parg1);
+		return rxval_evaluator_alloc_from_b_m_func(b_x_isnonemptymap_xfunc, parg1);
 	} else if (streq(fnnm, "length")) {
-		return rxval_evaluator_alloc_from_b_m_func(NULL/*xxx temp*/, parg1);
+		return rxval_evaluator_alloc_from_b_m_func(i_x_length_xfunc, parg1);
 	} else {
 		return NULL;
 	}
@@ -1170,7 +1168,7 @@ static rxval_evaluator_t* fmgr_alloc_xevaluator_from_binary_func_name(char* fnnm
 	rxval_evaluator_t* parg2)
 {
 	if (streq(fnnm, "haskey")) {
-		return rxval_evaluator_alloc_from_b_mx_func(NULL/*xxx temp*/, parg1, parg2);
+		return rxval_evaluator_alloc_from_b_mx_func(b_x_haskey_xfunc, parg1, parg2);
 	} else {
 		return NULL;
 	}
@@ -1198,6 +1196,8 @@ static void resolve_func_callsite(fmgr_t* pfmgr, rval_evaluator_t* pev) {
 
 	// xxx XXX builtin xev
 
+	// xxx XXX need to differentiate between map-in,map-out, map-in,scalar-out, and scalar-in,scalar-out
+
 	pevaluator = construct_builtin_function_callsite_evaluator(pfmgr, pcallsite);
 	if (pevaluator != NULL) {
 		*pev = *pevaluator;
diff --git a/c/dsl/rval_evaluators.h b/c/dsl/rval_evaluators.h
index 777104d89..c947c58ff 100644
--- a/c/dsl/rval_evaluators.h
+++ b/c/dsl/rval_evaluators.h
@@ -193,6 +193,7 @@ rxval_evaluator_t* rxval_evaluator_alloc_wrapping_rval(
 // rxval_func_evaluators.c
 
 rxval_evaluator_t* rxval_evaluator_alloc_from_variadic_func(xv_variadic_func_t* pfunc, rxval_evaluator_t** pargs, int nargs);
+rxval_evaluator_t* rxval_evaluator_alloc_from_b_x_func(xv_unary_func_t* pfunc, rxval_evaluator_t* parg1);
 rxval_evaluator_t* rxval_evaluator_alloc_from_b_m_func(xv_unary_func_t* pfunc, rxval_evaluator_t* parg1);
 rxval_evaluator_t* rxval_evaluator_alloc_from_b_mx_func(xv_binary_func_t* pfunc, rxval_evaluator_t* parg1,
 	rxval_evaluator_t* parg2);
diff --git a/c/dsl/rxval_func_evaluators.c b/c/dsl/rxval_func_evaluators.c
index 4d4e2b5e7..6c314b4d3 100644
--- a/c/dsl/rxval_func_evaluators.c
+++ b/c/dsl/rxval_func_evaluators.c
@@ -67,6 +67,39 @@ rxval_evaluator_t* rxval_evaluator_alloc_from_variadic_func(
 	return pxevaluator;
 }
 
+// ----------------------------------------------------------------
+typedef struct _rxval_evaluator_b_x_state_t {
+	xv_unary_func_t*  pfunc;
+	rxval_evaluator_t* parg1;
+} rxval_evaluator_b_x_state_t;
+
+static boxed_xval_t rxval_evaluator_b_x_func(void* pvstate, variables_t* pvars) {
+	rxval_evaluator_b_x_state_t* pstate = pvstate;
+	boxed_xval_t bxval1 = pstate->parg1->pprocess_func(pstate->parg1->pvstate, pvars);
+
+	return pstate->pfunc(&bxval1);
+}
+
+static void rxval_evaluator_b_x_free(rxval_evaluator_t* pxevaluator) {
+	rxval_evaluator_b_x_state_t* pstate = pxevaluator->pvstate;
+	pstate->parg1->pfree_func(pstate->parg1);
+	free(pstate);
+	free(pxevaluator);
+}
+
+rxval_evaluator_t* rxval_evaluator_alloc_from_b_x_func(xv_unary_func_t* pfunc, rxval_evaluator_t* parg1) {
+	rxval_evaluator_b_x_state_t* pstate = mlr_malloc_or_die(sizeof(rxval_evaluator_b_x_state_t));
+	pstate->pfunc = pfunc;
+	pstate->parg1 = parg1;
+
+	rxval_evaluator_t* pxevaluator = mlr_malloc_or_die(sizeof(rxval_evaluator_t));
+	pxevaluator->pvstate       = pstate;
+	pxevaluator->pprocess_func = rxval_evaluator_b_x_func;
+	pxevaluator->pfree_func    = rxval_evaluator_b_x_free;
+
+	return pxevaluator;
+}
+
 // ----------------------------------------------------------------
 typedef struct _rxval_evaluator_b_m_state_t {
 	xv_unary_func_t*  pfunc;