nvim: add empty? and update group

Until now you couldn't do `(tbl 1 2)`.
Now you can.

1 files changed, 18 insertions, 11 deletions

diff --git a/dot_config/nvim/fnl/toast/core.fnl b/dot_config/nvim/fnl/toast/core.fnl
index 54b0455..3c77e4a 100644
--- a/dot_config/nvim/fnl/toast/core.fnl
+++ b/dot_config/nvim/fnl/toast/core.fnl
@@ -12,6 +12,9 @@
    (each [i v (ipairs xs)]
     (when (> i n) (insert out v)))
    out))
+(fn empty? [xs]
+  "Returns true if the lengthable contains no elements."
+  (= 0 (length xs)))
 (fn first [xs]
   "The first element in a sequential table."
   (. xs 1))
@@ -21,27 +24,31 @@
 (fn group [n xs]
   "Group elements in xs in groups of n.
    Extra elements at the end will sit in the final group.
-   For example, (group 2 [1 2 3 4 5]) results in [[1 2] [3 4] [5]]."
-  (let [ll #(length (last $))
-        donext #(= (ll $) n)]
-   (accumulate [out [[]]
-                _ v (ipairs xs)]
-    (do (when (donext out)
-         (insert out []))
-        (insert (last out) v)
-        out))))
+   For example, (group 2 [1 2 3 4 5]) results in [[1 2] [3 4] [5]].
+   One exception is if xs is empty, in which case an empty collection is returned."
+ (if (empty? xs)
+   []
+   (let [ll #(length (last $))
+         donext #(= (ll $) n)]
+    (accumulate [out [[]]
+                 _ v (ipairs xs)]
+     (do (when (donext out)
+          (insert out []))
+         (insert (last out) v
+              out))))))
 (fn map [f xs]
   "Returns a sequential table consisting of the result of apply f to every item in xs."
   (accumulate [out []
                _ v (ipairs xs)]
    (let [mapped (f v)]
     (insert out (if (= 0 (select :# mapped))
-                     nil
-                     mapped)))))
+                    nil
+                    mapped)))))
 
 {: dec
  : inc
  : drop
+ : empty?
  : group
  : first
  : last}