Take UDFs out of build_expr and have Expression ensure Expression inputs

r/R/compute.R

@@ -381,7 +381,7 @@ register_scalar_function <- function(name, fun, in_type, out_type,
   # register with dplyr binding (enables its use in mutate(), filter(), etc.)
   register_binding(
     name,
-    function(...) build_expr(name, ...),
+    function(...) Expression$create(name, ...),
     update_cache = TRUE
   )
 

r/R/expression.R

@@ -171,7 +171,13 @@ Expression$create <- function(function_name,
                               args = list(...),
                               options = empty_named_list()) {
   assert_that(is.string(function_name))
-  assert_that(is_list_of(args, "Expression"), msg = "Expression arguments must be Expression objects")
+  # Make sure all inputs are Expressions
+  args <- lapply(args, function(x) {
+    if (!inherits(x, "Expression")) {
+      x <- Expression$scalar(x)
+    }
+    x
+  })
   expr <- compute___expr__call(function_name, args, options)
   if (length(args)) {
     expr$schema <- unify_schemas(schemas = lapply(args, function(x) x$schema))

r/tests/testthat/test-expression.R

@@ -58,9 +58,10 @@ test_that("C++ expressions", {
   # Interprets that as a list type
   expect_r6_class(f == c(1L, 2L), "Expression")
 
-  expect_error(
+  # Non-Expression inputs are wrapped in Expression$scalar()
+  expect_equal(
     Expression$create("add", 1, 2),
-    "Expression arguments must be Expression objects"
+    Expression$create("add", Expression$scalar(1), Expression$scalar(2))
   )
 })