Handle empty list in -reductions[-r]

dash.el

@@ -289,7 +289,7 @@ See also: `-reductions', `-reductions-r', `-reduce-r'"
 See `-reduce' for explanation of the arguments.
 
 See also: `-reductions-from', `-reductions-r', `-reduce-r'"
-  (-reductions-from fn (car list) (cdr list)))
+  (and list (-reductions-from fn (car list) (cdr list))))
 
 (defun -reductions-r-from (fn init list)
   "Return a list of the intermediate values of the reduction.
@@ -305,7 +305,11 @@ See also: `-reductions-r', `-reductions', `-reduce'"
 See `-reduce-r' for explanation of the arguments.
 
 See also: `-reductions-r-from', `-reductions', `-reduce'"
-  (-reductions-r-from fn (-last-item list) (-butlast list)))
+  (when list
+    (let ((rev (reverse list)))
+      (--reduce-from (cons (funcall fn it (car acc)) acc)
+                     (list (car rev))
+                     (cdr rev)))))
 
 (defmacro --filter (form list)
   "Anaphoric form of `-filter'.

dev/examples.el

@@ -340,24 +340,32 @@ new list."
     (--reduce-r (format "%s-%s" it acc) '()) => "nil-nil")
 
   (defexamples -reductions-from
-    (-reductions-from (lambda (a i) (format "(%s FN %s)" a i)) "INIT" '(1 2 3 4)) => '("INIT" "(INIT FN 1)" "((INIT FN 1) FN 2)" "(((INIT FN 1) FN 2) FN 3)" "((((INIT FN 1) FN 2) FN 3) FN 4)")
+    (-reductions-from (lambda (a i) (format "(%s FN %d)" a i)) "INIT" '(1 2 3 4)) => '("INIT" "(INIT FN 1)" "((INIT FN 1) FN 2)" "(((INIT FN 1) FN 2) FN 3)" "((((INIT FN 1) FN 2) FN 3) FN 4)")
     (-reductions-from 'max 0 '(2 1 4 3)) => '(0 2 2 4 4)
-    (-reductions-from '* 1 '(1 2 3 4)) => '(1 1 2 6 24))
+    (-reductions-from '* 1 '(1 2 3 4)) => '(1 1 2 6 24)
+    (-reductions-from '- 10 '(1)) => '(10 9)
+    (-reductions-from '- 10 ()) => '(10))
 
   (defexamples -reductions-r-from
-    (-reductions-r-from (lambda (i a) (format "(%s FN %s)" i a)) "INIT" '(1 2 3 4)) => '("(1 FN (2 FN (3 FN (4 FN INIT))))" "(2 FN (3 FN (4 FN INIT)))" "(3 FN (4 FN INIT))" "(4 FN INIT)" "INIT")
+    (-reductions-r-from (lambda (i a) (format "(%d FN %s)" i a)) "INIT" '(1 2 3 4)) => '("(1 FN (2 FN (3 FN (4 FN INIT))))" "(2 FN (3 FN (4 FN INIT)))" "(3 FN (4 FN INIT))" "(4 FN INIT)" "INIT")
     (-reductions-r-from 'max 0 '(2 1 4 3)) => '(4 4 4 3 0)
-    (-reductions-r-from '* 1 '(1 2 3 4)) => '(24 24 12 4 1))
+    (-reductions-r-from '* 1 '(1 2 3 4)) => '(24 24 12 4 1)
+    (-reductions-r-from '- 10 '(1)) => '(-9 10)
+    (-reductions-r-from '- 10 ()) => '(10))
 
   (defexamples -reductions
-    (-reductions (lambda (a i) (format "(%s FN %s)" a i)) '(1 2 3 4)) => '(1 "(1 FN 2)" "((1 FN 2) FN 3)" "(((1 FN 2) FN 3) FN 4)")
+    (-reductions (lambda (a i) (format "(%s FN %d)" a i)) '(1 2 3 4)) => '(1 "(1 FN 2)" "((1 FN 2) FN 3)" "(((1 FN 2) FN 3) FN 4)")
     (-reductions '+ '(1 2 3 4)) => '(1 3 6 10)
-    (-reductions '* '(1 2 3 4)) => '(1 2 6 24))
+    (-reductions '* '(1 2 3 4)) => '(1 2 6 24)
+    (-reductions '- '(1)) => '(1)
+    (-reductions '- ()) => ())
 
   (defexamples -reductions-r
-    (-reductions-r (lambda (i a) (format "(%s FN %s)" i a)) '(1 2 3 4)) => '("(1 FN (2 FN (3 FN 4)))" "(2 FN (3 FN 4))" "(3 FN 4)" 4)
+    (-reductions-r (lambda (i a) (format "(%d FN %s)" i a)) '(1 2 3 4)) => '("(1 FN (2 FN (3 FN 4)))" "(2 FN (3 FN 4))" "(3 FN 4)" 4)
     (-reductions-r '+ '(1 2 3 4)) => '(10 9 7 4)
-    (-reductions-r '* '(1 2 3 4)) => '(24 24 12 4))
+    (-reductions-r '* '(1 2 3 4)) => '(24 24 12 4)
+    (-reductions-r '- '(1)) => '(1)
+    (-reductions-r '- ()) => ())
 
   (defexamples -count
     (-count 'even? '(1 2 3 4 5)) => 2