factor out is_keras_tensor due to 2.0

Author: Sigrid Keydana

R/utils.R

@@ -224,14 +224,13 @@ keras_array <- function(x, dtype = NULL) {
     if (
       tf_version() >= "1.12" &&
       (
-        tensorflow::tf$contrib$framework$is_tensor(x) ||
-        is.list(x) && all(vapply(x, tensorflow::tf$contrib$framework$is_tensor, logical(1)))
+        is_keras_tensor(x) || is.list(x) && all(vapply(x, is_keras_tensor, logical(1)))
       )
     ) {
       return(x)
     }
   } else {
-    if ((keras_version() >= "2.2.0") && k_is_tensor(x)) {
+    if ((keras_version() >= "2.2.0") && is_keras_tensor(x)) {
       return(x)
     }
   }
@@ -381,3 +380,11 @@ as_shape <- function(x) {
       as.integer(d)
   })
 }
+
+is_keras_tensor <- function(x) {
+  if (is_tensorflow_implementation()) {
+    if (tensorflow::tf_version() >= "2.0") tensorflow::tf$is_tensor(x) else tensorflow::tf$contrib$framework$is_tensor(x) 
+  } else {
+    k_is_tensor(x)
+  }
+}