[elpa] externals/dash 8873749 120/316: Improve and simplify right-associative reductions

[ELPA Syncer]

branch: externals/dash
commit 88737493cd7fdded213b8fa2a3c2bf832dae9517
Author: Basil L. Contovounesios <contovob@tcd.ie>
Commit: Basil L. Contovounesios <contovob@tcd.ie>

    Improve and simplify right-associative reductions
    
    * Translate recursion to iteration to avoid exceeding
      max-lisp-eval-depth.
    
    * Rewrite functions in terms of anaphoric macros.
    
    * Expand test cases.
---
 dash.el         | 43 ++++++++++++++++++++-----------------------
 dev/examples.el | 40 +++++++++++++++++++++++-----------------
 2 files changed, 43 insertions(+), 40 deletions(-)

diff --git a/dash.el b/dash.el
index 8d1d9a6..e0437b8 100644
--- a/dash.el
+++ b/dash.el
@@ -205,7 +205,7 @@ Return nil, used for side-effects only."
   "Return the result of applying FN to INITIAL-VALUE and the
 first item in LIST, then applying FN to that result and the 2nd
 item, etc. If LIST contains no items, return INITIAL-VALUE and
-FN is not called.
+do not call FN.
 
 In the anaphoric form `--reduce-from', the accumulated value is
 exposed as symbol `acc'.
@@ -225,9 +225,9 @@ See also: `-reduce', `-reduce-r'"
 (defun -reduce (fn list)
   "Return the result of applying FN to the first 2 items in LIST,
 then applying FN to that result and the 3rd item, etc. If LIST
-contains no items, FN must accept no arguments as well, and
-reduce return the result of calling FN with no arguments. If
-LIST has only 1 item, it is returned and FN is not called.
+contains no items, return the result of calling FN with no
+arguments. If LIST contains a single item, return that item
+and do not call FN.
 
 In the anaphoric form `--reduce', the accumulated value is
 exposed as symbol `acc'.
@@ -237,6 +237,11 @@ See also: `-reduce-from', `-reduce-r'"
       (-reduce-from fn (car list) (cdr list))
     (funcall fn)))
 
+(defmacro --reduce-r-from (form initial-value list)
+  "Anaphoric version of `-reduce-r-from'."
+  (declare (debug (form form form)))
+  `(--reduce-from ,form ,initial-value (reverse ,list)))
+
 (defun -reduce-r-from (fn initial-value list)
   "Replace conses with FN, nil with INITIAL-VALUE and evaluate
 the resulting expression. If LIST is empty, INITIAL-VALUE is
@@ -246,20 +251,18 @@ Note: this function works the same as `-reduce-from' but 
the
 operation associates from right instead of from left.
 
 See also: `-reduce-r', `-reduce'"
-  (if (not list) initial-value
-    (funcall fn (car list) (-reduce-r-from fn initial-value (cdr list)))))
+  (--reduce-r-from (funcall fn it acc) initial-value list))
 
-(defmacro --reduce-r-from (form initial-value list)
-  "Anaphoric version of `-reduce-r-from'."
-  (declare (debug (form form form)))
-  `(-reduce-r-from (lambda (&optional it acc) ,form) ,initial-value ,list))
+(defmacro --reduce-r (form list)
+  "Anaphoric version of `-reduce-r'."
+  (declare (debug (form form)))
+  `(--reduce ,form (reverse ,list)))
 
 (defun -reduce-r (fn list)
   "Replace conses with FN and evaluate the resulting expression.
-The final nil is ignored. If LIST contains no items, FN must
-accept no arguments as well, and reduce return the result of
-calling FN with no arguments. If LIST has only 1 item, it is
-returned and FN is not called.
+The final nil is ignored. If LIST contains no items, return the
+result of calling FN with no arguments. If LIST contains a single
+item, return that item and do not call FN.
 
 The first argument of FN is the new item, the second is the
 accumulated value.
@@ -268,15 +271,9 @@ Note: this function works the same as `-reduce' but the 
operation
 associates from right instead of from left.
 
 See also: `-reduce-r-from', `-reduce'"
-  (cond
-   ((not list) (funcall fn))
-   ((not (cdr list)) (car list))
-   (t (funcall fn (car list) (-reduce-r fn (cdr list))))))
-
-(defmacro --reduce-r (form list)
-  "Anaphoric version of `-reduce-r'."
-  (declare (debug (form form)))
-  `(-reduce-r (lambda (&optional it acc) ,form) ,list))
+  (if list
+      (--reduce-r (funcall fn it acc) list)
+    (funcall fn)))
 
 (defun -reductions-from (fn init list)
   "Return a list of the intermediate values of the reduction.
diff --git a/dev/examples.el b/dev/examples.el
index 05669e9..7ae2d1f 100644
--- a/dev/examples.el
+++ b/dev/examples.el
@@ -303,34 +303,40 @@ new list."
 
   (defexamples -reduce-from
     (-reduce-from '- 10 '(1 2 3)) => 4
-    (-reduce-from (lambda (memo item)
-                    (concat "(" memo " - " (int-to-string item) ")")) "10" '(1 
2 3)) => "(((10 - 1) - 2) - 3)"
-                    (--reduce-from (concat acc " " it) "START" '("a" "b" "c")) 
=> "START a b c"
-                    (-reduce-from '+ 7 '()) => 7
-                    (-reduce-from '+ 7 '(1)) => 8)
+    (-reduce-from (lambda (memo item) (format "(%s - %d)" memo item)) "10" '(1 
2 3)) => "(((10 - 1) - 2) - 3)"
+    (--reduce-from (concat acc " " it) "START" '("a" "b" "c")) => "START a b c"
+    (--reduce-from (- acc it) 10 '(1 2 3)) => 4
+    (--reduce-from (- acc it) 10 '(1)) => 9
+    (--reduce-from (- acc it) 10 '()) => 10
+    (-reduce-from '- 7 '(1)) => 6
+    (-reduce-from '- 7 '()) => 7)
 
   (defexamples -reduce-r-from
     (-reduce-r-from '- 10 '(1 2 3)) => -8
-    (-reduce-r-from (lambda (item memo)
-                      (concat "(" (int-to-string item) " - " memo ")")) "10" 
'(1 2 3)) => "(1 - (2 - (3 - 10)))"
-                      (--reduce-r-from (concat it " " acc) "END" '("a" "b" 
"c")) => "a b c END"
-                      (-reduce-r-from '+ 7 '()) => 7
-                      (-reduce-r-from '+ 7 '(1)) => 8)
+    (-reduce-r-from (lambda (item memo) (format "(%d - %s)" item memo)) "10" 
'(1 2 3)) => "(1 - (2 - (3 - 10)))"
+    (--reduce-r-from (concat it " " acc) "END" '("a" "b" "c")) => "a b c END"
+    (--reduce-r-from (- it acc) 10 '(1 2 3)) => -8
+    (--reduce-r-from (- it acc) 10 '(1)) => -9
+    (--reduce-r-from (- it acc) 10 '()) => 10
+    (-reduce-r-from '- 7 '(1)) => -6
+    (-reduce-r-from '- 7 '()) => 7)
 
   (defexamples -reduce
     (-reduce '- '(1 2 3 4)) => -8
-    (-reduce (lambda (memo item) (format "%s-%s" memo item)) '(1 2 3)) => 
"1-2-3"
-    (--reduce (format "%s-%s" acc it) '(1 2 3)) => "1-2-3"
-    (-reduce '+ '()) => 0
-    (-reduce '+ '(1)) => 1
+    (-reduce 'list '(1 2 3 4)) => '(((1 2) 3) 4)
+    (--reduce (format "%s-%d" acc it) '(1 2 3)) => "1-2-3"
+    (-reduce '- '()) => 0
+    (-reduce '- '(1)) => 1
+    (--reduce (- acc it) '(1)) => 1
     (--reduce (format "%s-%s" acc it) '()) => "nil-nil")
 
   (defexamples -reduce-r
     (-reduce-r '- '(1 2 3 4)) => -2
-    (-reduce-r (lambda (item memo) (format "%s-%s" memo item)) '(1 2 3)) => 
"3-2-1"
-    (--reduce-r (format "%s-%s" acc it) '(1 2 3)) => "3-2-1"
+    (-reduce-r (lambda (item memo) (format "%s-%d" memo item)) '(1 2 3)) => 
"3-2-1"
+    (--reduce-r (format "%s-%d" acc it) '(1 2 3)) => "3-2-1"
     (-reduce-r '+ '()) => 0
-    (-reduce-r '+ '(1)) => 1
+    (-reduce-r '- '(1)) => 1
+    (--reduce (- it acc) '(1)) => 1
     (--reduce-r (format "%s-%s" it acc) '()) => "nil-nil")
 
   (defexamples -reductions-from