improve unpack_list error

R/dataframe__frame.R

@@ -143,10 +143,12 @@ NULL
 #' # custom schema
 #' pl$DataFrame(iris, schema = list(Sepal.Length = pl$Float32, Species = pl$Utf8))
 pl$DataFrame = function(..., make_names_unique = TRUE, schema = NULL) {
-  largs = unpack_list(...)
-
   uw = \(res) unwrap(res, "in $DataFrame():")
 
+  largs = unpack_list(...) |>
+    result() |>
+    uw()
+
   if (!is.null(schema) && !all(names(schema) %in% names(largs))) {
     Err_plain("Some columns in `schema` are not in the DataFrame.") |>
       uw()
@@ -633,7 +635,7 @@ DataFrame_sort = function(
 #'   (pl$col("Sepal.Length") + 2)$alias("add_2_SL")
 #' )
 DataFrame_select = function(...) {
-  .pr$DataFrame$select(self, unpack_list(...)) |>
+  .pr$DataFrame$select(self, unpack_list(..., .context = "in $select()")) |>
     unwrap("in $select()")
 }
 
@@ -740,7 +742,7 @@ DataFrame_shift_and_fill = function(fill_value, periods = 1) {
 #'   SW_add_2 = (pl$col("Sepal.Width") + 2)
 #' )
 DataFrame_with_columns = function(...) {
-  .pr$DataFrame$with_columns(self, unpack_list(...)) |>
+  .pr$DataFrame$with_columns(self, unpack_list(..., .context = "in $with_columns()")) |>
     unwrap("in $with_columns()")
 }
 
@@ -831,7 +833,11 @@ DataFrame_filter = function(...) {
 #' )
 DataFrame_group_by = function(..., maintain_order = pl$options$maintain_order) {
   # clone the DataFrame, bundle args as attributes. Non fallible.
-  construct_group_by(self, groupby_input = unpack_list(...), maintain_order = maintain_order)
+  construct_group_by(
+    self,
+    groupby_input = unpack_list(..., .context = "$group_by()"),
+    maintain_order = maintain_order
+  )
 }
 
 

R/functions__eager.R

@@ -62,7 +62,7 @@ pl$concat = function(
     ),
     rechunk = TRUE,
     parallel = TRUE) {
-  l = unpack_list(..., skip_classes = "data.frame")
+  l = unpack_list(..., skip_classes = "data.frame", .context = "in pl$concat")
 
   if (length(l) == 0L) {
     return(NULL)

R/group_by.R

@@ -89,7 +89,7 @@ GroupBy_agg = function(...) {
   .pr$DataFrame$by_agg(
     self = self,
     group_exprs = attr(self, "private")$groupby_input,
-    agg_exprs = unpack_list(...),
+    agg_exprs = unpack_list(..., .context = "in $agg():"),
     maintain_order = attr(self, "private")$maintain_order
   ) |>
     unwrap("in $agg():")

R/lazyframe__group_by.R

@@ -37,7 +37,7 @@ print.RPolarsLazyGroupBy = function(x, ...) {
 #'   pl$col("bar")$mean()$alias("bar_tail_sum")
 #' )
 LazyGroupBy_agg = agg = function(...) {
-  .pr$LazyGroupBy$agg(self, unpack_list(...)) |>
+  .pr$LazyGroupBy$agg(self, unpack_list(..., .context = "in $agg():")) |>
     unwrap("in $agg():")
 }
 

R/lazyframe__lazy.R

@@ -220,7 +220,7 @@ LazyFrame_describe_plan = "use_extendr_wrapper"
 #'   (pl$col("Sepal.Length") + 2)$alias("add_2_SL")
 #' )
 LazyFrame_select = function(...) {
-  .pr$LazyFrame$select(self, unpack_list(...)) |>
+  .pr$LazyFrame$select(self, unpack_list(..., .context = "in $select()")) |>
     unwrap("in $select()")
 }
 
@@ -246,7 +246,7 @@ LazyFrame_select = function(...) {
 #'   SW_add_2 = (pl$col("Sepal.Width") + 2)
 #' )
 LazyFrame_with_columns = function(...) {
-  .pr$LazyFrame$with_columns(self, unpack_list(...)) |>
+  .pr$LazyFrame$with_columns(self, unpack_list(..., .context = "in $with_columns()")) |>
     unwrap("in $with_columns()")
 }
 
@@ -977,7 +977,7 @@ LazyFrame_unique = function(subset = NULL, keep = "first", maintain_order = FALS
 #' )$
 #'   collect()
 LazyFrame_group_by = function(..., maintain_order = pl$options$maintain_order) {
-  .pr$LazyFrame$group_by(self, unpack_list(...), maintain_order) |>
+  .pr$LazyFrame$group_by(self, unpack_list(..., .context = "in $group_by():"), maintain_order) |>
     unwrap("in $group_by():")
 }
 
@@ -1060,7 +1060,8 @@ LazyFrame_sort = function(
     nulls_last = FALSE,
     maintain_order = FALSE) {
   .pr$LazyFrame$sort_by_exprs(
-    self, unpack_list(by), err_on_named_args(...), descending, nulls_last, maintain_order
+    self, unpack_list(by, .context = "in $sort():"), err_on_named_args(...),
+    descending, nulls_last, maintain_order
   ) |>
     unwrap("in $sort():")
 }
@@ -1517,7 +1518,7 @@ LazyFrame_profile = function(
 #' df$explode("numbers", "numbers_2")$collect()
 #' df$explode(pl$col(pl$List(pl$Float64)))$collect()
 LazyFrame_explode = function(...) {
-  dotdotdot_args = unpack_list(...)
+  dotdotdot_args = unpack_list(..., .context = "in explode():")
   .pr$LazyFrame$explode(self, dotdotdot_args) |>
     unwrap("in explode():")
 }

R/utils.R

@@ -89,22 +89,41 @@ verify_method_call = function(Class_env, Method_name, call = sys.call(1L), class
 #' trailing commas.
 list2 = list
 
+
+
+
 #' Internal unpack list
 #' @noRd
-#' @param l any list
+#'
+#' @param ... args to unwrap
+#' @param .context a context passed to unwrap
+#' @param .call  a call passed to unwrap
 #' @param skip_classes char vec, do not unpack list inherits skip_classes.
+#'
 #' @details py-polars syntax only allows e.g. `df.select([expr1, expr2,])` and not
 #' `df.select(expr1, expr2,)`. r-polars also allows user to directly write
 #' `df$select(expr1, expr2)` or `df$select(list(expr1,expr2))`. Unpack list
 #' checks whether first and only arg is a list and unpacks it, to bridge the
 #' allowed patterns of passing expr to methods with ... param input.
+#' Will throw an error if trailing comma.
 #' @return a list
 #' @examples
 #' f = \(...) unpack_list(list(...))
 #' identical(f(list(1L, 2L, 3L)), f(1L, 2L, 3L)) # is TRUE
 #' identical(f(list(1L, 2L), 3L), f(1L, 2L, 3L)) # is FALSE
-unpack_list = function(..., skip_classes = NULL) {
-  l = list2(...)
+unpack_list = function(..., .context = NULL, .call = sys.call(1L), skip_classes = NULL) {
+  l =
+    list2(...) |>
+    result() |>
+    map_err(\(err) {
+      if (identical(err$contexts()$PlainErrorMessage, "argument is missing, with no default")) {
+        err$plain("trailing argument commas are not (yet) supported with polars")
+      } else {
+        err
+      }
+    }) |>
+    unwrap(context = .context, call = .call)
+
   if (
     length(l) == 1L &&
       is.list(l[[1L]]) &&
@@ -116,6 +135,7 @@ unpack_list = function(..., skip_classes = NULL) {
   }
 }
 
+
 #' Convert dot-dot-dot to bool expression
 #' @noRd
 #' @return Result, a list has `ok` (RPolarsExpr class) and `err` (RPolarsErr class)